Marc Rayman
Marc Rayman
Chief Engineer/ Mission Director, JPL
Dawn Journal | January 29

by Marc Rayman


Dear Abundawnt Readers,

The dwarf planet Ceres is a giant mystery. Drawn on by the irresistible lure of exploring this exotic, alien world, Dawn is closing in on it. The probe is much closer to Ceres than the moon is to Earth.

And now it is even closer…

And now it is closer still!

What has been glimpsed as little more than a faint smudge of light amidst the stars for more than two centuries is finally coming into focus. The first dwarf planet discovered (129 years before Pluto), the largest body between the sun and Pluto that a spacecraft has not yet visited, is starting to reveal its secrets. Dawn is seeing sights never before beheld, and all of humankind is along for the extraordinary experience.

We have had a preview of Dawn’s approach phase, and in November we looked at the acrobatics the spacecraft performs as it glides gracefully into orbit. Now the adventurer is executing those intricate plans, and it is flying beautifully, just the way a seasoned space traveler should.

Dawn’s unique method of patiently, gradually reshaping its orbit around the sun with its ion propulsion system is nearly at its end. Just as two cars may drive together at high speed and thus travel at low speed relative to each other, Dawn is now close to matching Ceres’ heliocentric orbital motion. Together, they are traveling around the sun at nearly 39,000 mph (almost 64,000 kilometers per hour), or 10.8 miles per second (17.4 kilometers per second). But the spaceship is closing in on the world ahead at the quite modest relative speed of about 250 mph (400 kilometers per hour), much less than is typical for interplanetary spaceflight.

Animated Gif of Ceres

Dawn observed Ceres for an hour on Jan. 13, from a distance of 238,000 miles (383,000 kilometers). A little more than half of the surface was revealed as Ceres rotated. This imaging session is known as OpNav 1. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA/PSI

Dawn has begun its approach imaging campaign, and the pictures are wonderfully exciting. This month, we will take a more careful look at the plans for photographing Ceres. Eager readers may jump directly to the summary table, but others may want to emulate the spacecraft by taking a more leisurely approach to it, which may aid in understanding some details.

While our faithful Dawn is the star of this bold deep-space adventure (along with protoplanet Vesta and dwarf planet Ceres), the real talent is behind the scenes, as is often the case with celebrities. The success of the mission depends on the dedication and expertise of the members of the Dawn flight team, no farther from Earth than the eighth floor of JPL’s building 264 (although occasionally your correspondent goes on the roof to enjoy the sights of the evening sky). They are carefully guiding the distant spacecraft on its approach trajectory and ensuring it accomplishes all of its tasks.

To keep Dawn on course to Ceres, navigators need a good fix on where the probe and its target are. Both are far, far from Earth, so the job is not easy. In addition to the extraordinarily sophisticated but standard methods of navigating a remote interplanetary spacecraft, using the radio signal to measure its distance and speed, Dawn’s controllers use another technique now that it is in the vicinity of its destination.

From the vantage point of Earth, astronomers can determine distant Ceres’ location remarkably well, and Dawn’s navigators achieve impressive accuracy in establishing the craft’s position. But to enter orbit, still greater accuracy is required. Therefore, Dawn photographs Ceres against the background of known stars, and the pictures are analyzed to pin down the location of the ship relative to the celestial harbor it is approaching. To distinguish this method from the one by which Dawn is usually navigated, this supplementary technique is generally known as “optical navigation.” Unable to suppress their geekiness (or, at least, unmotivated to do so), Dawn team members refer to this as OpNav. There are seven dedicated OpNav imaging sessions during the four-month approach phase, along with two other imaging sessions. (There will also be two more OpNavs in the spiral descent from RC3 to survey orbit.)

The positions of the spacecraft and dwarf planet are already determined well enough with the conventional navigation methods that controllers know which particular stars are near Ceres from Dawn’s perspective. It is the analysis of precisely where Ceres appears relative to those stars that will yield the necessary navigational refinement. Later, when Dawn is so close that the colossus occupies most of the camera’s view, stars will no longer be visible in the pictures. Then the optical navigation will be based on determining the location of the spacecraft with respect to specific surface features that have been charted in previous images.

To execute an OpNav, Dawn suspends ion thrusting and turns to point its camera at Ceres. It usually spends one or two hours taking photos (and bonus measurements with its visible and infrared mapping spectrometer). Then it turns to point its main antenna to Earth and transmits its findings across the solar system to the Deep Space Network.

Animated gif of series of images of Ceres takien by Dawn spacecrat on Jan. 25, 2015

This animation of Ceres rotating was made by combining images taken by the Dawn spacecraft on Jan. 25 over the course of one hour in OpNav 2. Dawn was 147,000 miles (237,000 kilometers) from Ceres.

While it is turning once again to resume ion thrusting, navigators are already starting to extract information from the images to calculate where the probe is relative to its destination. Experts update the design of the trajectory the spacecraft must follow to reach its intended orbital position and fine-tune the corresponding ion thrust flight plan. At the next communications session, the revised instructions are radioed back across the solar system, and then the reliable robot carries them out. This process is repeated throughout the approach phase.

Dawn turned to observe Vesta during that approach phase more often than it does on approach to Ceres, and the reason is simple. It has lost two of its four reaction wheels, devices used to help turn or stabilize the craft in the zero-gravity, frictionless conditions of spaceflight. (In full disclosure, the units aren’t actually lost. We know precisely where they are. But given that they stopped functioning, they might as well be elsewhere in the universe; they don’t do Dawn any good.)

Dawn’s sentient colleagues at JPL, along with excellent support from Orbital Sciences Corporation, have applied their remarkable creativity, tenacity and technical acumen to devise a strategy that allows all the original objectives of exploring Ceres to be met regardless of the condition of the wheels, even the (currently) healthy ones. Your correspondent refers to this as the “zero reaction wheel plan.” One of the many methods that contributed to this surprising resilience was a substantial reduction in the number of turns during all remaining phases of the mission, thus conserving the precious hydrazine propellant used by the small jets of the reaction control system. Guided by their successful experience at Vesta, experts determined that they could accommodate fewer OpNavs during the approach to Ceres, thus saving turns. (We will return to the topic of hydrazine conservation below.)

The images serve several purposes besides navigation. Of course, they provide a tantalizing preview of the intriguing world observed from Earth since 1801. Each picture whets our appetite! What will Ceres look like as it comes into sharper focus? Will we see evidence of a subsurface ocean? What unexpected shapes and structures will we find? What strange new features will show up? Just what is that bright spot? Quite simply: we don’t know. It would be a pretty good idea to send a spacecraft there to find out!

Scientists scrutinize all the photos for moons of Ceres, and OpNavs 3 – 7 will include many extra images with exposures chosen to help reveal moons. In addition, hundreds more pictures will be taken of the space around Ceres in the hours before and after OpNav 3 to allow an even more thorough search.

On two occasions during the approach, Dawn will take images and spectra throughout a complete Ceres rotation of slightly over nine hours, or one Cerean day. During that time, Dawn’s position will not change significantly, so it will be almost as if the spacecraft hovers in place as the dwarf planet pirouettes beneath its watchful eye, exhibiting most of the surface. These “rotation characterizations” (known by the stirring names RC1 and RC2) will provide the first global perspectives.

As Dawn flies into orbit, it arcs around Ceres. In November, we described the route into orbit in detail, and one of the figures there is reproduced here. Dawn will slip into Ceres’ gravitational embrace on the night of March 5 (PST). But as the figure shows, its initial elliptical orbit will carry it to higher altitudes before it swoops back down. As a result, pictures of Ceres will grow for a while, then shrink and then grow again.

Dawn Trajectory

Dawn’s approach trajectory. We are looking down on the north pole of Ceres. The sun is off the figure far to the left. The spacecraft flies in from the left and then is captured on the way to the apex of its orbit. It gets closer to Ceres during the first part of its approach but then recedes for a while before coming in still closer at the end. Lighting by the sun is not depicted here, but when Dawn is on the right side of the figure, it only sees a crescent of Ceres, which is illuminated from the left. (The white circles are at one-day intervals.) Credit: NASA/JPL

Because of the changing direction to Ceres, Dawn does not always see a fully illuminated disk, just as the moon goes through its familiar phases as its position relative to the sun changes. The hemisphere of the moon facing the sun is bright and the other is dark. The half facing Earth may include part of the lit side and part of the dark side. Sometimes we see a full moon, sometimes gibbous, and sometimes a thin crescent.

The table shows what fraction of Ceres is illuminated from Dawn’s perspective. Seeing a full moon would correspond to 100 percent illumination. A half moon would be 50 percent, and a new moon would be zero percent. In OpNav 6, when Ceres is 18 percent illuminated, it will be a delicate crescent, like the moon about four days after it’s new.

Four views of Ceres taken by the Hubble telescope

Four views of Ceres as it rotates, as seen with Hubble Space Telescope, were the best we had before OpNav 2. All of Dawn’s pictures from now on will show finer detail. Credit: NASA, ESA, J. Parker (Southwest Research Institute), P. Thomas (Cornell University), and L. McFadden (University of Maryland, College Park)

OpNav images of a narrow crescent won’t contain enough information to warrant the expenditure of hydrazine in all that turning. Moreover, the camera’s precision optics and sensitive detector, designed for revealing the landscapes of Vesta and Ceres, cannot tolerate looking too close to the sun, even as far from the brilliant star as it is now. Therefore, no pictures will be taken in March and early April when Dawn is far on the opposite side of Ceres from the sun. By the end of April, the probe will have descended to its first observational orbit (RC3), where it will begin its intensive observations.

The closer Dawn is to Ceres, the larger the orb appears to its camera, and the table includes the (approximate) diameter the full disk would be, measured in the number of camera pixels. To display greater detail, each pixel must occupy a smaller portion of the surface. So the “resolution” of the picture indicates how sharp Dawn’s view is.

We also describe the pictures in comparison to the best that have been obtained with Hubble Space Telescope. In Hubble’s pictures, each pixel covered about 19 miles (30 kilometers). Now, after a journey of more than seven years through the solar system, Dawn is finally close enough to Ceres that its view surpasses that of the powerful telescope. By the time Dawn is in its lowest altitude orbit at the end of this year, its pictures will be well over 800 times better than Hubble’s and more than 600 times better than the OpNav 2 pictures from Jan. 25. This is going to be a fantastic year of discovery!

Beginning of activity in Pacific Time zone Distance from Dawn to Ceres in miles (kilometers) Ceres diameter in pixels Resolution in miles (kilometers) per pixel Resolution compared to Hubble Illuminated portion of disk Activity
Dec 1, 2014 740,000
(1.2 million)
9 70
0.25 94% Camera calibration
Jan 13, 2015 238,000
27 22
0.83 95% OpNav 1
Jan 25 147,000
43 14
1.3 96% OpNav 2
Feb 3 91,000
70 8.5
2.2 97% OpNav 3
Feb 12 52,000
121 4.9
3.8 98% RC1
Feb 19 28,000
221 2.7
7.0 87% RC2
Feb 25 25,000
253 2.3
8.0 44% OpNav 4
Mar 1 30,000
207 2.9
6.5 22% OpNav 5
Apr 10 21,000
304 2.0
9.6 18% OpNav 6
Apr 15 14,000
455 1.3
14 50% OpNav 7


Some of the numbers may change slightly as Dawn’s trajectory is refined and even as estimates of the strength of Ceres’ gravitational tug improve. (Dawn is already feeling that pull, even though it is not yet in orbit.) Still, this should help you fill out your social calendar for the next few months.

To get views like those Dawn has, you can build your own spaceship and fly it deep into the heart of the main asteroid belt to this intriguing world of rock and ice. Or you can visit our Ceres image gallery to see pictures as soon as they are released. If you chose the first option, use your hydrazine wisely!

As we discussed above, to explore Ceres without the use of the reaction wheels that were essential to the original design, mission controllers have worked very hard to conserve hydrazine. Let’s see how productive that effort has been. (You should be able to follow the story here without careful focus on the numbers. They are here for the more technically oriented readers, accountants and our old friends the Numerivores.)

Dawn launched in Sept. 2007 with 101 pounds (45.6 kilograms) of hydrazine. The ship escaped from Vesta in Sept. 2012, four weeks after the second reaction wheel failed during the climb out of Vesta’s gravitational hole. (By the way, Dawn is now more than one thousand times farther from Vesta than it is from Ceres. It is even farther from Vesta than Earth is from the sun!) At the beginning of the long interplanetary flight to Ceres, it still had 71.2 pounds (32.3 kilograms) left. As it had expended less than one-third of the original supply through the end of the Vesta expedition, that might seem like plenty. But it was not. Without the reaction wheels, subsequent operations would consume much more hydrazine. Indeed, engineers determined that even if they still had the entire amount that had been onboard at launch, it would not be enough. The Ceres objectives were at serious risk!

The flight team undertook an aggressive campaign to conserve hydrazine. They conceived more than 50 new candidate techniques for reducing hydrazine consumption in the 27-month journey to Ceres and the 18 months of Ceres operations and systematically but quickly assessed every one of them.

The team initially calculated that the long interplanetary flight between the departure from Vesta and the beginning of the Ceres approach phase would consume 27.6 pounds (12.5 kilograms) of hydrazine even if there were no errors, no glitches, no problems and no changes in the plans. Following the intensive conservation work, they determined that the spacecraft might instead be able to complete all of its assignments for only 9.7 pounds (4.4 kilograms), an astonishing 65 percent reduction. (Keep track of that mass through the end of the next paragraph.) That would translate directly into more hydrazine being available for the exploration of Ceres. They devised many new methods of conducting the mission at Ceres as well, estimating today that it will cost less than 42.5 pounds (19.3 kilograms) with the zero reaction wheel plan. (If the two remaining wheels operate when called upon in the lowest orbit, they will provide a bonus reduction in hydrazine use.)

Dawn’s two years and four months of interplanetary cruise concluded on Dec. 26, 2014, when the approach phase began. Although the team had computed that they might squeeze the consumption down to as low as 9.7 pounds (4.4 kilograms), it’s one thing to predict it and it’s another to achieve it. Changes to plans become necessary, and not every detail can be foreseen. As recounted in October, the trip was not entirely free of problems, as a burst of cosmic radiation interrupted the smooth operations. Now that the cruise phase is complete, we can measure how well it really went. Dawn used 9.7 pounds (4.4 kilograms), exactly as predicted in 2012. Isn’t flying spacecraft through the forbidding depths of the interplanetary void amazing?

This success provides high confidence in our ability to accomplish all of the plans at Ceres (even if the remaining reaction wheels are not operable). Now that the explorer is so close, it is starting to reap the rewards of the daring 3.0-billion-mile (4.9-billion-kilometer) journey to an ancient world that has long awaited a terrestrial emissary. As Dawn continues its approach phase, our growing anticipation will be fueled by thrilling new pictures, each offering a new perspective on this relict from the dawn of the solar system. Very soon, patience, diligence and unwavering determination will be rewarded with new knowledge and new insight into the nature of the cosmos.

Dawn is 121,000 miles (195,000 kilometers) from Ceres, or half the average distance between Earth and the moon. It is also 3.63 AU (338 million miles, or 544 million kilometers) from Earth, or 1,390 times as far as the moon and 3.69 times as far as the sun today. Radio signals, traveling at the universal limit of the speed of light, take one hour to make the round trip.

Dr. Marc D. Rayman
7:00 p.m. PST January 29, 2015

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158 Responses to “Dawn Journal | January 29”

  1. Gene says:

    Why have there been no posts/pictures/News since 3 March 2015.
    Did something break?

    • Prior Semblance says:

      It actually explains why on this very page.

      “the camera’s precision optics and sensitive detector … cannot tolerate looking too close to the sun … Therefore, no pictures will be taken in March and early April when Dawn is far on the opposite side of Ceres from the sun.”

  2. Doug says:

    You can bet no alien base, ufo, or even H2o here cause we wouldn’t even be seeing these photos. Now if for some reason when they get close and they lose contact or video feed then that would be suspicious ?

  3. NYCKerbal says:

    Hey Marc, et al –

    An inspirational mission. Thank you all!

    I think in one of Bill Bryson’s books he pointed out that, unlike many pictures we’ve seen of asteroid belt, with hundreds of rocks tumbling about very close to one another, they are in fact really very, very far apart.

    How close is Ceres’ next neighbor? And how large is it? Is there any chance Dawn may smack into some small bit of rock we don’t know about? And is there a way for her to avoid it if she is?

    • Marc Rayman says:

      I am a big fan of Bill Bryson’s books. As it turns out, I’ve also written that the asteroid belt is quite unlike the way it’s often depicted in movies. See, for example, these comments and the links included there. I addressed the risk from smaller objects here. Thanks to the difference between science fiction and science fact, Dawn is very safe from rocks large and small.


  4. Matt says:

    Dear Dr. Rayman,

    this is a sensation! Did you help to discover an alien light house on Ceres? :-)

    The old large basin can be easily recognized. It looks very relaxed and flattened (as many of the larger craters). A proof for an ice shell beneath surface?


    • Marc Rayman says:

      Hi Matt,

      I don’t know what we’ve discovered yet, but it’s going to be wonderful to find out. If it’s aliens, I will invite them to post comments here (and perhaps especially on my December description of Ceres).

      That large basin is very interesting. I think it’s too early to claim proof of anything, however. We don’t know yet why it appears the way it does. There are several possible explanations. We need more detailed, quantitative information, and that is still to come. For example, as a reminder, much of Dawn’s work in its third observational orbit (from August to October) will be focused on making topographical maps, so that will give us an excellent understanding of the shape of this basin.


  5. Andrew R Brown. says:

    Good Afternoon (my time) Marc and everyone else on here,

    I still keep looking at those two images from the RC1 and keep being mesmerized by them. Ever since being aware of the Asteroid Belt in my childhood, I always wondered what the individual members looked like.

    When the Galileo Spacecraft showed us in astonishing detail Asteroid 951 Gaspra, a huge success at a first attempt, not just a handful of cruddy images barely a few pixels wide in the distance, 951 Gaspra was seen in great detail, in colour too from several viewing geometries. From 951 Gaspra to now 1 Ceres, the big daddy of the belt now showing quite considerable detail from RC1.

    Looking forward to what the RC 2 images will reveal. 21 Lutetia, the first really large asteroid seen up close by the huge successful ESA Rosetta spacecraft now at Comet 67 P Churyumov – Gerasimenko, to 4 Vesta was a real revelation, 1 Ceres also proving to be, still to me looking much like one of the moons of Saturn, Uranus or Neptune (still have an inkling of being an ejected moon of Uranus or Neptune or perhaps a former KBO).

    I suspect now, that the RC1 images were mnore than good enough to show a plethora of surface features, naming of features should now start to happen as it will be easier to reference features come RC 3 and the lower orbits to come afterwards.

    The almost ‘ghost’ basin in the first image still intruiges me and looking forward to seeing more structure in the craters with central peaks as well as the tiny fresh craters showing as bright spots.

    Andrew R Brown. Ashford, Kent, United Kingdom.

    Has any progress been made as yet to search for possible moons?

    • Marc Rayman says:

      Hi Andrew,

      Yes, I’m sure some features will receive formal names soon (as a reminder for others, I explained in December what the basis for names will be). For now, informal names are being used. Official designations usually are not established simply on the basis of observation. Names will be submitted by the Dawn project to the International Astronomical Union when the features are planned to be the subject of publications. For context, this map of Vesta, from Dawn’s exploration in 2011-2012, shows all the official names. We can see that there are many features without names.

      Yes, progress has indeed been made on the search for moons. All of the images have been given careful investigation, and more study lies ahead. So far, no moons have been sighted.


      • Andrew R Brown says:

        Thank You very much Marc,

        Of course the word Cereal is a derivative. :D

        Crater names will be very interesting for sure on that theme.

        Thank you very much also for stating that no moons have been found as yet. I did not seriously expect that to be answered as yet as that may have been embargoed information and you went beyond the call of duty. :D

        If there are any, then they are tiny, miniscule, but I think at this late stage 1 Ceres is certainly moonless and will turn out to be so. Still worth looking though in further OpNavs.

        Andrew R Brown. Ashford, Kent, United Kingdom.

  6. Peter Collins says:

    If you blow up the latest images, selecting only the white spots and then with an image editor color invert the images so that bright areas appear black, and then adjust contrast and sharpness, you will see that only a liquid could form these shapes. In other words you will see “lakes” and “channels”, obviously frozen over after the initial melting, probably caused by impact events or other phenomena, but certainly only the result of a liquid medium filling depressions. These white spots are not elevated mountains of ice in my humble opinion. If you want to see images of what I am describing, download from my Dropbox here:

  7. Matt Gibbons says:

    Dawn it is!

    RC2 looks like it’s gonna be good. Hoping for images over the weekend, if not sooner. Which brings me to a question about manpower and budgets. Is the Dawn team (once orbit has been achieved) a 24/7 operation with three shifts or is the team tied to scheduling of activities done within budgetary constraints, i.e. are weekends off with a skeleton crew keeping an eye out for any anomalies?

    Just curious about the human factors in the equation and of course what limitations are put on the team by politically mandated fiscal constraints.

    Does the Dawn team also collaborate with international organizations like ESA? Is the entire operation on the campus at JPL?


    • Marc Rayman says:

      Hi Matt,

      Image releases will occur only on normal NASA/JPL work days, which do not include weekends. As I have explained in comments below, there are many steps in the process to release them, both in the US and Germany, so RC2 pictures will not be available this week. They have not yet even made their way from the asteroid belt to Earth yet (and it is after 11:00 pm PST on Thursday).

      Dawn is budgeted for single shift operations. (As I described, we did split into multiple shifts for the contingency operations following the cosmic ray strike in September). The details of the scheduling are complicated for several reasons, including when we have DSN coverage. We try to keep on a normal work schedule. Dawn has been flying for nearly 7.5 years, and Ceres operations will extend for well over a year. Everyone knows the results of human factors studies, especially for a long project like this. A conventional schedule is best for the happiness of the dedicated members of the team, and it is best for their ability to perform their challenging work. Of course, we can’t always do that. Everyone is prepared to be contacted at any time if need be. Each individual is committed to the success of our ambitious mission and does whatever is necessary to achieve that. Readers who followed Dawn’s exciting adventure at Vesta in 2011 and 2012, as well as the interplanetary cruise, know that the team has always responded promptly and extremely effectively whenever the spacecraft needed unplanned help! But Dawn’s expedition has generally gone very smoothy, so such incidents are not common. (We also rehearse contingency operations to keep our skills sharp.)

      Almost everyone on the operations team is at JPL. We have a few members at UCLA, and Orbital ATK contributes specialized expertise to the mission as well. Planetary Science Institute leads the operation of the gamma ray and neutron spectrometer. ESA is not involved in the Dawn project, but we do have partners in Italy and Germany. They provided the visible and infrared mapping spectrometer and the camera, respectively, and are essential to the operation of those instruments. Members of the science team are distributed around the US and those two countries as well.

      I hope this answers all of your questions. I appreciate your interest in so many details!


      • Romana Starfield says:

        That was very interesting and cool to read Marc. I haddn’t put much thought into the human side of the mission. I know the team is obviously dedicated, but didn’t realise it was a mostly office hours job. I too had been wondering if images were processed and released on week ends. I had been wondering why we’ve only seen the two images from the 12th. Obviously it takes a while to transmit the data, then staff have to be avaliable and so on. I figure like many government agencies it is a case of having to do more with less.
        Again, well done to the very dedicated team.

        • Marc Rayman says:

          Thank you, Romana!

          Because missions generally are so successful (isn’t that cool?), perhaps many people don’t consider how challenging some of them really can be nor how much work it actually takes. Once again, we do whatever is needed, whenever it is needed. There is nothing routine or familiar about entering orbit around and exploring a huge, alien world that has never before received a visitor from Earth, not even by a flyby spacecraft.

          Along the lines of how demanding the work can be, I hope you and others will understand if I scale back on answers to questions.


          • Matt Gibbons says:

            I think I can speak for everyone on this blog when I say, thank you for your patience and for your time in addressing our questions and comments. I also feel that everyone here would, in unison say, if you need to scale back, then you should scale back and let the blog take care of itself for however many weeks and months you’ll be managing something much more important…the discoveries that lie ahead regarding the truth of 1 Ceres! And that is what you are Marc, a truth seeker…no question. It’s evident in everything you’ve given to this blog, and it’s evident in your entire philosophy. But that’s the nature of exploration, the nature of science and the search for things as they are, not as we would wish them (or dream them) to be! With each new step we learn more about ourselves and where we came from and ultimately where we’re going. Each new mission is an advancement of truth and the beauty that it reveals.

            No reply please…I just felt the need to thank you.


            • Romana Starfield says:

              I agree. By all means you should scale back. I (and I am sure others) would completely understand. I now also understand why you refer to past answers for similar questions. I have read the various “Where will Dawn go next / can’t you extend the mission” question several times (Indeed I asked it myself) and have seen you handle it so well and with such patience.

              No answer needed either. I’m very happy with what has been written thus far. No extra info needed for me.

  8. Hello Marc,
    I admire that he answers all the questions,
    that at every New Photos increase ..
    I do not want to ask a New questions, but I can not ..:-p
    I wonder .. In OPNAV3 illuminated portion of the disk is 97%, and in RC1 is 98%, but to me it seems to be the opposite .. OpNav3 showed entire disk of Ceres, in RC1 and it seems much less ..
    Daniele – Italy

    • Marc Rayman says:

      Hi Daniele,

      The difference in illumination is quite small, and our eyes tend not to be very good at making these kinds of discriminations. You may be tricked by other differences between the pictures, including the brightness, variations in surface features and more.


  9. Dave says:

    Hi, If there is enough fuel after inserting orbit of Ceres and doing all the necessary science there, can you speculate how many pounds of hydrazine might remain if the two reaction wheels are working? And would it be enough to go to and possibly orbit a moon of Jupiter should NASA allocate funds to support such an extended mission?


    • Marc Rayman says:

      Hi Dave,

      Even if the two reaction wheels operate well, the best use of the remaining hydrazine will be to continue to observe Ceres from our low altitude orbit. This is a huge, fascinating world, and we will not run out of productive observations to perform. Even in the most optimistic case, there would not be sufficient hydrazine to permit Dawn to go anywhere else nearly as worthwhile. For more on this, see this comment below and my preview of the end of the mission.


  10. Wow, words are not enough. At long last I think this is the first of many images to come that shows Ceres in its true form. I have to say, it is both spectacular and beautiful. Long have I waited for my second favourite place in this universe to be revealed beyond being just a fuzzy blob. I can see craters, some mountains, mysterious white spots and there’s just more to come. I’m so glad I made it this far in this extraordinary adventure. Kudos to all of those in the team, in NASA and the other agencies that made this possible.
    Like others, I eagerly await more.

    • Sean Deany says:

      I agree Romana.

      Its been a long time in waiting to see a clear image showing in some greater detail features and forms on the surface of 1 Ceres. The left image – in the two hemisphere views clearly shows the so called Piazzi region which may turn out to be a signature chaos field. The numerous white spots on 1 Ceres have been puzzling for over a decade and may be revealed in this image as water ice subliming due to even micro meteorite strikes. Look forward to colour images and a global grid system soon.

      • While I think cryvolcanos would be amazing, I suspect these will be impact sites. This may seem an unusual assumption, but I base it on Earth’s moon. There are some bright craters like Tycho which appear as a relativly light white spot in comparison to the surrounding terrain. If I understand what I have read correctly, Ceres is relativly dark. I suspect the white spots are also reasonably dark, just lighter in comparison with everything else on Ceres.
        However, whatever they are, they are indeed proving to be a fascinating mystery. If they were cryo volcanos that would be cool. I could imagine 200-300 years hence that people will be saying; “Forget the Martian ice caps, Ceres is where it is at for the snow!”

  11. May Roberts says:

    Hi Marc, your post is brilliant as usual. I wish more space missions had great writers like you on their team.

    Could the white spots be salt left by evaporating water from a cryovolcano? I assume the water would have a lot of dissolved minerals which would stay behind, making a kind of bright salt plain. If the volcano isn’t active right now, the deposits would be dry so they wouldn’t produce water vapor.

    • Marc Rayman says:

      Thank you for nice comment, May!

      Yes, I believe it is possible that the bright spots could be from what you describe. That is one of the intriguing ideas that will be tested with the more detailed pictures and other data Dawn will provide us soon.


  12. Matt Gibbons says:


    One final question for today. What is the total Delta-V expected from Dawn’s ion propulsion system, once it has completely depleted it’s xenon gas? Or perhaps it’s best to ask what the delta-v is estimated to be after the hydrazine runs out? You expect to not use up all of the xenon before that, correct?

    Just curious regarding the total propulsion expected of Dawn vs the next best example of a chemical rocket. Sorry if you’ve answered this fifty times…but there is so much on the blog it’s rather daunting to just go back and read through the whole thing…and thus we (me) bug you with questions you’ve already answered.

    By the way, it seems to me your more capable than lucky…although luck always plays a part in human endeavors. What I mean is, you’ve paid your dues to sing the blues (so to speak)…I know you earned the right to be where you are through hard work and years of study. SO…thanks for all the blood, sweat and tears! We are all the better for it.



    • Marc Rayman says:

      Hi Matt,

      For others, delta-v is the notation for change (delta) in velocity (v). This is a measure of how effective a propulsion system is, and it describes how much maneuvering a spacecraft can do. It is thanks to the very high delta-v of Dawn’s ion propulsion system that it can accomplish this unique mission of orbiting two extraterrestrial destinations. But readers may want to be aware that there are conceptual pitfalls here. I have written more about this in many Dawn Journals, including this explanation of the speed and how we use the ion propulsion to climb what I like to call the solar system hill.

      Dawn will have little need for ion thrusting after it spirals down to its lowest altitude orbit near the end of this year. By then, the total delta-v will be more than 24,000 mph (nearly 11 kilometers per second). This is about 2.5 times the greatest propulsive delta-v by any other spacecraft, with the previous record holder being the first interplanetary mission to use ion propulsion, Deep Space 1. To put Dawn’s delta-v into perspective, visit the link in the paragraph above.

      Yes, I certainly appreciate that there are one or two readers who haven’t followed the mission from the beginning and memorized each and every word along the way. I know it’s not easy to catch up. I do try to provide links for people who want to understand these topics better. I don’t have time to explain them again, and I want to give as many people as possible the opportunity to understand these fun discussions.

      Thank you for your message about my contribution. It’s nice of you, and your comment does mean a lot to me. I will not say any more about this, but I think it is a matter of luck even to have the drive to work hard and study hard, not to mention the opportunities to do so and the capability to take advantage of it all. Regardless, it is very gratifying to know that my hard work is appreciated.


  13. André Meunier says:

    Could there be snow on Ceres? The albedo from the bright spots look very high, the metadatas from the picture are not given so I have no reference and I am no specialist anyway. But here is what I think: When Ceres goes toward perihelion some water sublimates and form a thin atmosphere. When it goes back to aphelion it recrystallizes loosely, just like snow, at the coolest spots. As water reservoirs would be the first place to cool down it would de the place where this phenomenon would most likely occur. I had already put this idea under a comment on an article on aver 10 hours ago (pseudo TechnoCreed) and feel good enough to bring it here. Great work on that wonderful mission.

  14. Paul Kuenstler says:

    Image intensities are manipulated, so the posted images could be misleading. Are there any estimates yet for albedos of the prominent “bright” areas?

    • Marc Rayman says:

      Hi Paul,

      For others, the albedo is a measure of how reflective the area is, and there are a few comments about this below. Ceres reflects about nine percent of the sunlight. Based on RC1 pictures, the brightest spot seems to have an albedo of around 25%, or roughly three times Ceres’ average reflectivity. Of course, when we obtain higher resolution pictures, it may turn out that it is really a smaller and even brighter feature.


      • Matt Gibbons says:

        Correct me if I’m wrong Marc, but doesn’t Enceladus hold the record for the highest albedo of any object in the solar system. Or was it Europa? I believe the number was 99%. I suspect if Enceladus were in orbit around the Earth it would be pretty dazzling…but then, it is only about 15% of the diameter of the Moon at about 300 miles in diameter, so it would be more like a really powerful searchlight I would think. Of course, it would be unlikely to survive for long in the inner solar system with daylight temperatures on our Moon topping out at about 250 deg F. It would basically turn into the most incredible comet in history!


        • Marc Rayman says:

          Yes, you’re thinking of Enceladus, Matt, not Europa.

          In order to manage my time (and, if I can, maybe even find enough time to write another Dawn Journal :-) ), I prefer to devote my responses to questions more directly related to Dawn. I invite other people to participate in these other discussions if they wish.


  15. David Cronin says:

    The latest images are very intriguing, can’t wait for more! The white spots could be cryovolcanism perhaps? Would Ceres retain enough internal heat to drive such processes?

    • Marc Rayman says:

      As I described in December, David, it is possible that cryovolcanism (“cold volcanism”) occurs on Ceres, and I mentioned below that there has been a great deal of analysis of the internal heat. Still, the answers depend on many details we do not yet understand.

      When you raise the possibility of cryovolcanism, I presume you have in mind that the spots are chemical or structural remnants. Although I do not want to delve into this speculation, I should be clear that I do not believe the bright spots are active cryovolcanoes.


  16. Andrew R Brown says:

    WOW Marc,

    These are incredible images and to think that nearly twice as good again will be obtained THIS Thursday :D

    1 Ceres certainly has impact craters of many sizes right down to the current limit of resolution are very plentiful. On the left image, there is a partial rim of a very degraded, ghost impact basin, in the northern hemisphere, my guess was at least 300 KM / 186 miles wide when formed.

    The right image shows some nice complex craters, with central peaks.

    The northern hemisphere (north is to the left in these images I assume) is showing a lot more detail now, as I expected, many more impact craters are showing. 1 Ceres to me is now looking like a love child between the Saturn moon Rhea and Uranus moons Umbriel and Oberon.

    To me 1 Ceres does not look like a typical Asteroid Belt resident, I still think maybe a former KBO or even more likely an escaped moon of Uranus or Neptune.

    Will we get to see the entire movie or at least the images taken 90 degrees from those released today?

    Andrew R Brown, Ashford, Kent, United Kingdom.

    • Marc Rayman says:

      Hi Andrew,

      I agree with you: WOW. Well put!

      There is no particular reason Ceres should look like a typical asteroid belt resident. We already know it is not at all like asteroids. It has nearly four times the mass of the second most massive resident, Vesta, which we know from Dawn’s exploration also is quite unlike typical asteroids. Vesta is more like a small planet. Describing Ceres and Vesta as asteroids can mislead people. That is why I rarely refer to them that way. Both are widely considered to be protoplanets, very different from the rocks people think of as asteroids.

      All of Dawn’s pictures of Ceres will be released, just as we released all of them from Vesta. The science team is working to share the images with the public as promptly as they can. As I explained in the comment immediately below, it does take some time.


    • Sean Deany says:

      Wonderful images Marc,

      Andrew’s references to those moons of Uranus as comparison is quite right. Several years ago I read a similar references as speculation on what the surface of Ceres may look like – who ever that was must be dancing around the room right now.

      These two latest images it appears that if one rotates them some 45% clockwise we get the correct north orientation at the top of each image. Concerning this and finding the longitude degree is another issue I am hoping your team can present as of the RC2 survey. Would love to see a reference grid as it would assist in defining features. For instance the area known as Region A is centred at approx Longitude E 235 degrees / Latitude N 22 degrees based from ESA Herschel observatory. Will such information be available soon.

      • Andrew R Brown says:

        Hi Sean,

        It might have been me with those theories about 1 Ceres looking like some of the moons of Uranus. To me 1 Ceres does look more at home in orbit around Uranus or Neptune rather than within the Asteroid Belt. Perhaps 1 Ceres is a protoplanet that did form close to the current orbit, but sure to me looks like an imposter within the Asteroid Belt.

        The real clincher were the RC1 images published so far, though I thought the OpNav3, Wednesday 4th February 2015 images were more than good enough to make me think my long held predictions on the appearance of 1 Ceres were correct.

        The RC2 images are going to be very special indeed, the white spots certainly will be shown to be fresh impact craters where space weathering has not had time as yet to darken the relatively recently exposed ice rich material.

        The ‘fat crescent’ phase of the OpNav 4 imagery next Thursday is going to be awesome. I hope we get to see at least a large proportion of the lit side go through a rotation. A crescent 1 Ceres will be awesome.

        I share Marc’s notion that we are all on this journey together. :D

        Andrew R Brown. Ashford, Kent, United Kingdom.

    • Matt says:

      Hello Andrew! Hello Marc!

      Is there a chance that Uranus moon escaped into inner solar system in its earlier phase? I learned that there is a theory that the giant planets changed its position in this period. What was the reason that Uranus rotates on “its side”? May this event propelled a moon towards asteroid belt?

      It is pity that we have no better data from Uranus moons, which can compared to Ceres! It is time to send an orbiter to the forgotten planet Uranus.


      • Andrew R Brown says:

        Hi Matt,

        There is an idea that the four giant planets were once closer together, with Neptune inwards from Uranus. Jupiter put on mass quickly towards the end of the planetary formative period, speeding up Saturn, in turn disrupting Neptune. Neptune over time was put into a more elliptical orbit before tidal influences with Uranus caused them to swap places.

        Uranus is thought to have been ‘knocked’ over with a collision by an object roughly Earth massed. Myself I think Uranus was knocked over when it was still small near the beginning of it’s formation and formed on it’s side, that way a very much smaller object was involved, perhaps a Triton, Pluto or Eris type world could have done it, more likely in my opinion. Perhaps if indeed 1 Ceres was a former Uranus moon was ejected shortly after this time when the infant Uranus was subjected to tidal influences when Neptune was being ‘moved’ further out by Jupiter and Saturn ‘sorting’ themselves out.

        Another possibility is that 1 Ceres is a former KBO, a brethren of the larger KBOs like Pluto, Eris, Quaoar, Varuna, etc. In fact 1 Ceres is very close in size to Quaoar, as well as the Pluto moon Charon, Uranus moons Ariel and Umbriel and Saturn moons Dione and Tethys.

        1 Ceres is looking more that Tethys or Umbriel more than the others. Perhaps 1 Ceres was ejected from the Kuiper Belt by Neptune when Neptune ran into the former inner part of the Kuiper Belt, before ending up some time later closer to the Sun in the Asteroid Belt. 2 Pallas seems another oddball.

        The Saturn moon Phoebe certainly was either a former KBO or was a former moon of Uranus or Neptune before being captured by Saturn.

        Andrew R Brown.

        • Matt says:

          Thank you Andrew for detailed response! I hope there will in next 15 years a flyby-mission to Pallas (“meeting point “, where Pallas cross the ecliptic). May be such a mission could combined with other targets.

          • Andrew R Brown. says:

            Hi Matt,

            I suspect you are aware of a Discovery Mission proposal to orbit the huge Main Belt Asteroid 16 Psyche, almost certainly an exposed core of a former huge asteroid / proto dwarf planet. 16 Psyche is over 98% iron, with what appears to be a portion of lower mantle still attached to one area.

            This mission would be the first to a metallic asteroid, the first to see an exposed core, will put into context very well what DAWN observed at 4 Vesta, regarding internal mass of 4 Vesta, revealling a dense core, also MESSENGER at Mercury, orbiters at venus, insight to the Earth’s inner core, possibly Mars too and the galilean moons, Io, Europa and Ganymede of Jupiter.

            I sincerely hope this mission is approved and would be something if on route to 16 Psyche the craft makes a close pass of 2 Pallas at one of the nodes. 2 Palleas also has extreme seasons, I think has an axial tilt of approx 70 degrees, so would be great if near an equinox, rather than a Solstice like Voyager 2 did with the Uranus system or 21 Lutetia as Rosetta went past.

            Andrew R Brown. Ashford, Kent, United Kingdom.

            • Marc Rayman says:

              Hi Andrew,

              There are many very interesting Discovery proposals. I don’t want to delve into proposals or other missions here, but I should mention that the team for the Psyche mission is not considering a visit to Pallas.


              • Andrew R Brown. says:

                Good Afternoon Marc and everyone on here,

                I did not seriously expect the proposed 16 Psyche craft to encounter 2 Pallas, was just thinking out aloud and throwing a few ideas around. :D

                I think that ALL capable outer solar system bound craft should encounter at least one Main Belt asteroid, if could be a real large one like 2 Pallas, 5 Astraea, 6 Hebe (thought to be very red), 7 Iris, 8 Flora, 9 Metis (possible exposed core), 10 Hygeia, etc, then all the better. :) Perhaps the ESA JUICE may take up the batton, or the proposed NASA Europa Clipper or even the proped NASA Io Volcano observer?

                I hope we get to see some more 1 Ceres imagery soon from DAWN. Not only am looking forward to the RC2 images but also the OpNav 4 imagery showing a 44% crescent 1 Ceres. I understand this is not a complete rotation, however will still be fascinating to see.

                I will certainly be staying for the entire ride.

                Andrew R Brown. Ashford, Kent, United Kingdom.

                • Marc Rayman says:

                  Hi Andrew,

                  It certainly would be neat if missions could encounter asteroids, and I share your eagerness to see what they would discover! Nevertheless, the costs to such visits can be very high. Those costs can come in many forms in addition to financial, including reducing the overall scientific return of the mission by undertaking complicated diversions that distract from or diminish the primary objectives. In some cases, of course, such encounters would even be impossible, but other people may not recognize that. I know you were presenting a fun idea, and I appreciate that. I simply wanted to provide a definitive statement to prevent a rumor from starting from someone who might read your interesting comment. It would be nice if the people who worked on the Psyche proposal might avoid having to deal with the same kind of persistent and erroneous rumors about Dawn possibly going to Pallas.

                  You won’t have to wait long to see more of Dawn’s images of Ceres.

                  I’m glad you’re along for the ride. Many exciting rewards lie ahead!


  17. Robert Griner says:

    Hello Dr. Marc,

    First let me say that I very much appreciate the blend of hard facts and goofiness that you bring to your journals and blogs. You make rocket science so much fun! Now, the question: what can you tell us about color? The Hubble photos of Ceres make the dwarf planet seem so earth-like with hints of brown and blue. I have read that these hues could be photographic “artifacts” based on the magnification. As the dwarf planet zooms into view, we are witnessing monochrome images of an orb that looks not too different from our own moon. When does technicolor arrive at Ceres and what do you think we will see?

    • Marc Rayman says:

      Hi Robert,

      I’m grateful for your kind message, and I’m glad you enjoy my style. Rocket science is fun, but it isn’t always as accessible as it could be. Part of what I try to do in my writing and in my public presentations is help people see how wonderful it is.

      Most of Dawn’s pictures in the approach phase are monochrome (that is, black and white). We do take some color views in RC1 and RC2, and we will get many, many more during the course of the mission at Ceres. The science team has the responsibility of analyzing and interpreting the pictures both for the conduct of the mission and for scientific publication. The need for accuracy and scientific review of the data slows the interpretation and release of the photos. I’ve written a few times that I prefer not to speculate much here — I’ll leave that to others who enjoy doing so and may have more free time than I do :-) Nevertheless, I think that when we see color pictures adjusted to show how Ceres would look to our eyes, it will show very little color. It will mostly be varying shades of gray. Perhaps there will be some localized regions that have hints of color.


  18. Hello Marc
    I have LookED the New fantastic images of Ceres (RC1);
    What thing leaves so ‘puzzled the scientists? (said Chris Russell)?
    have estimated the exact diameter and the temperature of the planetary body?
    Many Thanks,
    Daniele bianchino

    • Marc Rayman says:

      Hi Daniele,

      What leaves Chris Russell puzzled is what puzzles the rest of us: what are those bright spots? There is speculation (including on this blog), but we don’t know. He had thought that perhaps the improved resolution of RC1 would resolve the mystery.

      We do not yet have a refined diameter, but in one of my next couple of Dawn Journals, I will give an update to the size and mass (which also will affect the orbits we fly to). The measurement of the temperature will come from analysis of the infrared spectra, but it is too soon to have results.


  19. Matt Gibbons says:

    Whoa…the reveal begins! Ceres is coming into sharp focus and it appears there’s lots of exploration ahead. Which leads me to a comment about the great white spot. I looks like a splash crater that uncovered subsurface ice. Even if it isn’t that, it looks as if the other white-ish features are impact related. Also, it appears that there are remains of a very large impact, perhaps as big as half the diameter of Ceres. The left image shows degraded arcuate ridges that appear to be quite ancient. There appear to be multiple large impacts in the same general area as the degraded crater rim that looks to be about half Ceres’ diameter (roughly).

    I envy you Marc…it’s the happy man who works at what he loves. Even more so when it involves exploration on the cutting edge of science!

    Congratulations Marc, looks like you’re going to be a very busy man over the next weeks, months and years!


    • Andrew R Brown says:

      Hi Matt,

      Yes there is certainly a huge ancient degraded ‘ghost’ basin in the left image.

      The ‘Arctuate Scarps’ to me look like degraded rims of ancient large ‘ghost’ craters.

      The surface of 1 Ceres is looking very ancient for sure, well see more fore sure as DAWN draws ever closer. Fascinating . :D

      Andrew R Brown. Ashford, Kent, United Kingdom.

      • Matt Gibbons says:

        Hello Andrew,

        I tend to prefer the term “arcuate ridges” based on common usage in lunar and planetary texts. They are definitely not scarps, they are basically the remains of large impact bodies that are now only identifiable by their remaining crater rims.

        The term “ghost basin or crater” would say to me that the basins or rims had been completely flooded (or buried) and could only be revealed using deep penetrating radar. Finding ghost craters would be a triumph…like some of the large basins on the Moon that have left little visible above lava flooded Mare.

        My favorite supposition is that the Oceanus Procellarum is actually a very large basin. A basin so large that it might be the largest in the entire solar system! Perhaps 3200 km across? Now THAT is a ghost basin! There is a great deal of skepticism regarding whether OP is a basin…but I like to argue the point.



        • Andrew R Brown. says:

          Hi Matt,

          I have always unsterstod ‘Ghost’ basins and craters to be largely, almost obliterated features , maybe not quite 100% buried or erased, but nearly so.

          I would say that the OP on the moon IS a gigantic basin.

          Andrew. :D

    • Marc Rayman says:

      Thank you, Matt. I appreciate your kind sentiments. I must admit that, having loved space exploration and science for my whole life, sometimes I do feel this is a dream come true. It is incredibly cool! (If you’re interested in a personal description of how cool another space adventure was, go here and search on the page for “incredibly cool.”) I recognize how lucky I am. And yet, as I’ve written elsewhere (including below just a few hours ago), we can all share in this. That has been a theme in many of my Dawn Journals. (See the end of this as one of many examples.) You’re involved in this extraordinary expedition too, Matt. I’m glad you are, and I’m glad you find it so exciting. I would congratulate us all on appreciating the power of science and the profundity of reaching so far from our humble home. We are all lucky to be able to participate in a culture that values such grand undertakings.


      • Matt Gibbons says:

        Funny, when I was observing space missions in the 60’s and 70’s I was as excited about the Soviet Unions successes as I was for the US achievements. The Lunokhod missions were my favorite Soviet success…to this day no one has topped those robotic missions. Too bad that the Lunar Rovers of the Apollo missions weren’t able to operate independently after the Ascent stages took the astronauts home.

        I’m a fan of space exploration and am happy when any country achieves great things in space. We’re all human beings regardless of nationality and politics, and human beings are capable of great things. The Dawn mission is an extension of all that came before it, and is a harbinger of more to come. If I die tomorrow, I’ll be happy to have lived in this time, the age when space travel was mastered and the solar system was revealed in all it’s stunning glory.


        • Marc Rayman says:

          Very well stated, Matt! I share your enthusiasm for the space activities of other countries. To me, what matters is humankind exploring the universe, and I am thrilled by all successes. You might get a kick out of The Planetary Society’s informal video tour of my private space collection at home, where I show a few of my personal treasures representing our species’ ventures into the cosmos.


  20. PJ Crepeau says:

    Dear Marc,
    Congratulations on the spectacular results to your years-long exploration of the Asteroid Belt with the Dawn Spacecraft! You have every right to be proud of your contribution to solar system science.
    And kudos to your remarkable engineers around the world for their extraordinary hardware and software.
    I understand you have found ways to conserve significant amounts of hydrazine fuel, which begs the question: Does the spacecraft have much xenon left for the ion engines? And if so, could the spacecraft possibly be sent to yet another asteroid (pending funding, of course)?
    Thanks for the exceptional work from you and your first-rate team.

    • Marc Rayman says:

      Thank you for your generous comments, Pierre! You’re very kind. To me, more important than any individual’s personal pride is that everyone can share in this exciting adventure, whether they work on the mission or not. I have written about that in many of my Dawn Journals and in this additional blog, and it is what I consider most significant of all. I have been a space enthusiast my whole life, and the reason I devote so much of my free time to public communication is that I know how much it means to those not directly involved in a mission to be able to follow it. I’m glad you are along for the adventure!

      I explained the spacecraft’s fate here. In brief, given the loss of reaction wheels, Dawn needs to use hydrazine to orient itself, so when the hydrazine is expended, the spacecraft will no longer be able to point its solar arrays at the sun, its main antenna at Earth, its sensors at Ceres or its ion engine in the direction needed to maneuver to a new destination. As I described, the best use of the remaining hydrazine at the end of the primary mission would be to continue to observe Ceres. Dawn will remain a permanent companion of the dwarf planet.

      Thank you again for your message!


  21. Matt says:

    Dear Dr. Rayman,

    great, that is the next step of disclosure Ceres’ secrets. It seems to me that most of Ceres’ craters are relaxed and flattened, especially near the equator (different to Uranus’ moons?)!

    That would mean that the regolith layer is thin and covers an ice shell, in which the craters are graved. However, I am not an expert and I am keen to listen to those in next days and weeks.



  22. AmbiValent says:

    Is arrival at Ceres defined as the moment when Dawn is so close Ceres would win the tug-of-war with the Sun, or when it wouldn’t escape Ceres if the drive was turned off, or is there yet another definition? (tried to post this before, didn’t show)

    • Marc Rayman says:

      Hi Frank,

      We have a formal, technical definition of arrival, but it amounts to the same as both of your definitions. At arrival, Dawn is in orbit around Ceres, so if it stopped ion thrusting, it would not escape. To me, that sounds the same as your tug-of-war with the sun. (There is a technical subtlety there, but I presume you mean that Ceres can hang on to Dawn despite the sun’s pull.)

      Arrival is not only a matter of being close to Ceres. To enter orbit, Dawn needs to achieve a certain combination of distance, speed and direction of travel that together allow Ceres’ gravity to take hold. Our carefully plotted course is designed to ensure that all conditions are met. I described our unique method of entering orbit here.

      I hope this answers your question.


  23. Stephen Sullivan says:


    Thank you for all the hard work you have put into this dawnting task!!! Your input – and the blog itself – have made me feel like I have rejoined my Summer Astronomy Class again (UMCP – DR. ROSE). What a treat!

    As such (i.e. with many of what seem to be the most important questions having now been posited) I simply wish to ask if you will post you next ‘monthly’ journal update after OPNAV5? I ask only because you usually post right before the end of the month though doing so this month would cut us out of OPNAV5 (the last major photographic event for 6 weeks or so..).

    Thanks again for your enthusiasm and hard work.

    • Marc Rayman says:

      I greatly appreciate your kind message, Stephen.

      I’ve never found it to be very easy to squeeze the Dawn Journals into my schedule, but I do hope to post one earlier in March than I otherwise would. Regardless of when I write it, however, OpNav 5 pictures will be available here as soon as the science team releases them. You can enjoy the view without waiting for my blog.

      Science is my first love, and it is the reason for conducting the mission, but I am going to continue to focus my writing on the mission. There will be many press releases and other publications presenting the discoveries about Ceres, and there are many people on the science team who will describe the findings. But there are few other places that explain or chronicle the extraordinary adventure itself. Even during the times of the mission that we are not returning pictures, the distant spacecraft will be engaged in activities I hope will be interesting to people who yearn for a cosmic adventure.

      Thank you again for your support and your interest!


  24. Luis says:

    Oh Dear!

    This is one of the few times when a Federal Holiday comes to delay “the party”. The new imagery data must be already in the computers on Earth, but … we have to wait….

    By the way, is all the processing done at JPL, imagery wise, or are there other partners elsewhere that also contribute in the analysis and preparation of the raster data?


    • Marc Rayman says:

      Hi Luis,

      All data from Dawn come through the Deep Space Network to JPL. JPL routes the data from the instruments to the organizations responsible for processing them into usable forms (images, spectra, etc.). Our partners at the Max Planck Institute for Solar System Research in Germany provided the camera, so that is where the bits are transformed into cool pictures.


  25. Mark Raphael says:

    Hi Marc:

    Thank-you and Thanks to the entire DAWN team; for the many years of hard work, planning, designing and working on the DAWN mission. It is because of the efforts of the DAWN team, that the rest of us can now experience the wonders of DAWN’s mission and share in a greater understanding of our solar system.

    When I think of the Dawn Blog, I am reminded of a ‘Foreword’ Albert Einstein wrote. To paraphrase, (much of popular science is either too simple, that it loses it’s meaning, or too complicated that it looses it’s readers. What is left is not much, but it is very valuable.)

    I would say that this blog has hit that sweet spot. :)

    Looking foward to the many discoveries ahead.


  26. Jorrie says:

    Marc, interesting journal, thanks!

    I noticed on the DSN site that the Dawn downlink data rate is about 125 kbits/sec on the 8.44 GHz channel. I’m interested in how long it takes to send down the typical images, in other words how large is such a download session typiclally?


    • Marc Rayman says:

      Hi Jorrie,

      The time to transmit a picture depends on the details of the image, because the spacecraft compresses the data, but generally it is between one and two minutes. The full analysis of the pictures for scientific purposes, however, requires additional information from the spacecraft. In addition, to keep our distant robotic explorer healthy, we scrutinize myriad measurements of currents, voltages, temperatures, switch positions, pressures, valve positions, software states, instructions it has executed, decisions it has made, and much more. Following RC1, it took Dawn about 16 hours to download all of its Ceres observations plus this additional information.

      As you know, no one antenna can point at Dawn for 16 hours, just as you cannot point at the sun, moon or a star for that long. Earth rotates too quickly. To return the data yesterday and today, we used the three largest antennas of the Deep Space Network, each 230 feet (70 meters) in diameter. We started with the one in Canberra, Australia, then moved over to the one in Madrid, Spain, and concluded in Goldstone, California.

      Thank you for your interest!


  27. Bat says:


    First, thanks for your work, and this blog&Journal ^^

    Today is the first “rotation characterizations”, and some interressing images will come, I hope ^^

    But you mention some “spectral caracterizations” too, which one for RC1? Infrared? Or some other “science” instruments? ^^

    • Marc Rayman says:

      Thank you for your comment, Bat.

      I share your interest in seeing the images from this rotation characterization. I am sure they will be very interesting! In all the OpNavs and rotation characterizations, Dawn collects bonus measurements with the mapping spectrometer. The device really is two spectrometers packaged in one unit, providing spectra in both visible and infrared.


  28. Scott Q says:

    WTG Marc! Just saw the new pics today, you guys are getting really, really close.

    I’m still remember the old DS1 days, this is every bit exciting.

    Keep up the good work.


    • Marc Rayman says:

      Thank you, Scott. Yes, Dawn is exciting!

      I know you also shared in the wonderful mission of Deep Space 1, the first interplanetary mission to use ion propulsion and other advanced, high-risk technologies like artificial intelligence. It also acquired NASA’s first close-up pictures of the nucleus of a comet. I’m glad you remain so interested!


  29. Andrew R Brown says:

    Hi Marc,

    It is certainly turning out that 1 Ceres is as I expected, long before the launch of DAWN, a cratered, largely unevolved protoplanet.

    1 Ceres is turning out to be much like the Uranus moon Umbriel, dark, cratered with a few fresher impact craters appearing as bright spots, much like we are seeing 1 Ceres during the approach.

    This will be fascinating as the craters will tell us much about the history of 1 Ceres and that part of the Asteroid Belt.

    There has been speculation that 1 Ceres is from the Kuiper Belt and was sent sunward when the four giant outer planets ‘sorted’ themselves out when Jupiter put on mass quickly towards the end of the formative period, Saturn to a lesser extent with the orbital purtabations caused Neptune and Uranus (note the order being reverse of how they are now)to swing outwards, swap places and Neptune ran into the former inner portion of the Kuiper Belt scattering objects large and small, some impacting Mercury, forming Caloris, Tolstoj and Rembrandt basins, Valhalla and Asgard basins on the Jupiter moon Callisto, marial basins on our Moon, Hellas and Argyre basins on Mars, Gallieo Regio and Marius Regio on the Jupiter moon Ganymede, etc.

    Possibly maybe delivering much of the water in Earth’s oceans (there is some doubt cast by the Rosetta spacecraft at Comet 67P/Churyumov–Gerasimenko, though this is based on only one comet.

    Certainly the Neptune moon Triton and Saturn moon Phoebe are former Kuiper Belt Objects and have heard suggestions that Phoebe could even be a former moon of either Uranus or Neptune that was ‘captured’ by the much more massive Saturn when they were being ‘sorted’. I wonder if 1 Ceres could also be a former Uranus or Neptune moon that was ejected and ended up being shunted around the outer solar system before being ‘inserted’ into a heliocentric ‘sweet spot’ in the Asteroid Belt?

    Can DAWN determine from the geologically young bright impact crater in the northern hemisphere that has been so obvious in the DAWN approach imagery to date as well as Hubble Space Telescope observations the abundance of Heavy Water and Deuterium in any possible exosphere? Would be interesting to compare with the abundance in Earth’s oceans and Comet 67P/Churyumov–Gerasimenko.

    I will be back after tomorrow’s images have been returned.

    Andrew R Brown. Ashford, Kent, United Kingdom.

    • Marc Rayman says:

      Hi Andrew,

      Dawn cannot distinguish deuterium from hydrogen. Our neutron spectrometer can measure the abundance of hydrogen in the uppermost yard (meter) or so of the surface, but there will not be enough deuterium to register.

      Making any measurement of water vapor above Ceres will be extremely challenging for Dawn. This probe was designed to explore solid, airless worlds.


    • Matt says:

      Dear Mr. Brown,

      yes, it is true, there seems to be a significant similarity to Uranus’ moon Umbriel in surface appearances at this stage status of imaging, but I sustain my hope that Ceres is different in detail and for example more geological active also in present time!


      • Andrew R Brown says:

        Thank You both very much Marc and Matt.

        Yes, I agree that DAWN is still too far away from 1 Ceres to draw too many conclusions.

        However the Wednesday 4th February 2015 images for me are certainly more than good enough to show a great many definite features.

        My initial impression is that 1 Ceres is much like the Uranus moon Umbriel, which was very well seen by Voyager 2 considering her passing high speed and very low lighting levels and the quality of the DAWN images on the 4th are not that far off those images.

        Those obtained on Thursday 12th February 2015 will surpass those and be similar in resolution to the Voyager 2 images of the Uranus moon Titania where more detail was very apparent.

        Can I ask, would it be possible in the interim to post up four images of 1 Ceres obtained on the 12th, 90 degrees apart. I understand it will take time to put together the entire Rotation movie and perhaps do likewise for the images to be obtained on Thursday 19th February 2015.

        This is becoming far too interesting now.

        Thank You very much :D

        Andrew R Brown, Ashford, Kent, United Kingdom.

        • Marc Rayman says:

          Hi Andrew,

          We will post pictures on this website and elsewhere as soon as all the necessary steps are complete. After receiving the data, the team has to process the images before making them public, following established processes. Monday is a federal holiday, so some of the steps will not be possible before Tuesday.

          In the meantime, it seems that the OpNav 3 images are continuing to provide plenty of material for interesting and entertaining discussions. If you think it’s becoming too interesting now, just wait! The views are going to improve throughout the year as Dawn spirals to lower and lower altitudes (just as we did at Vesta). By the end of this year, in the lowest orbit, the resolution will be almost 400 times better than the OpNav 3 pictures. You might find that even more interesting :-)


  30. Sean Deany says:

    Hi Marc,

    By studying the best images so far from DAWN and based on my earlier speculations based on Hubble images I have come to conclusion that the northern hemisphere of Ceres is indeed a sub-surface ocean. This yes is obvious, while it may be that the southern hemisphere generally is “dry” – just rocky material with the exception of some icey material thinly dispersed. The white spots appear to be only in the northern hemisphere, therefore evident of possibly this water / convection icey material. They couldn’t be geysers as Ceres would have outgassed its self billions of years ago, while they must certainly have some relation to the sub-surface ocean. Therefore the white spots must be some residue due to the effect from a form of venting other than geysers – more so other forms of outgassing which is teneous (as evident in the 2013 Herschel findings). What I believe we are looking at when it comes to these numerous white spots, predominantly in the northern hemisphere, are what on Earth would be called white smokers! This of course is being highly optimistic and does point to evidence for a Cerian biosphere. The scientific consensus says that Ceres likely has a sub-surface ocean and probably a rocky core of silicate material. From my understanding the white smokers of the mid Atlantic ridge are the effects of not volcanism, but a chemical process where there is some heating nonetheless. So I’m putting my bets on that the white spots of Ceres are more likely to be long term chemical points of process rather than fresh impacts or geysers as we known them on Earth.

    • Andrew R Brown says:

      Hi Sean,

      I think a subsurface ocean on 1 Ceres is extremely unlikely.

      There are two main reasons that make me extremely doubtful.

      1). 1 Ceres is not being tidally heated like the Jupiter moons Io and Europa (I even have doubts about Europa having a global subsurface ocean, subsurface lakes yes, not ocean) and Io is well known for the huge volcanoes and lava lakes. 1 Ceres is in a long term stable orbit with no massive tidal influences, so tidal heating will not be happening and any possible early subsurface ocean would have frozen solid hundreds of millions of years ago.

      2). 1 Ceres will not have nearly enough radioisotopes to generate enough heat to keep a subsurface ocean liquid.

      The images tomorrow will help, remember the Sun is shining almost head on much like a nearly full moon, so what may appear the be a largely smooth area in the northern hemisphere on 1 Ceres, is certainly as heavily cratered as the areas seen near the south pole. We’ll see.

      Andrew R Brown. Ashford, Kent, United Kingdom.

      • Sean Deany says:

        Hi Andrew,

        I should have made myself a little more clear, as when I said sub-surface ocean I should have said that it would indeed be in a solid state – frozen! Of course Ceres is to isolated from large planets like Jupiter for tidal forces and would no longer have significant radioactive decay in its core to create a liquid ocean. I believe that there may be some chemical processes where this water ice ocean meets the solid rocky material of the core and / or outer core. There may be some mineralogical heating process going on from where convection ice and even water flows via channels towards the surface. The white spots indeed must be areas of water vapor venting out into space, but the brightness may in fact be salt or calcium deposits etc. I’m not expert however.

        • Marc Rayman says:

          Hi Sean and Andrew,

          Your speculations are entertaining!

          I would not be quite as quick to reach conclusions about a subsurface ocean. Science is pretty powerful, and the possibility of large reservoirs of liquid water deep beneath the surface is still considered a credible possibility. This is based on sophisticated mathematical modeling of the interior and surface of Ceres, including the effects of radioactive materials incorporated at formation, various combinations of chemical constituents, how heat flows, the effects of incident sunlight, and many more factors. Pictures during the approach phase are not sharp enough to indicate anything about the deep interior. Think of how little you could infer about the interior structure of our planet from images like those Dawn has obtained of Ceres. Reaching conclusions about what lies far below the surface of Ceres will need to be informed by what we learn with Dawn’s more extensive studies. To me, this seems like a good reason to get into orbit and explore this mysterious world!


        • Matt Gibbons says:

          I am wondering why there is no discussion of carbon dioxide ice. I believe the published estimates of the surface temperature of 1 Ceres are (white) spot on for CO2 ice. There seems to be a bias in favor of water, but Marc has already confirmed that there isn’t enough water vapor based on data from Herschel. I previously wrote that “CO2 sublimates to a solid at 194 deg K, which is within the temperature range of Ceres (168-235 deg K), correct?” These temps seem to be a key…but I certainly could be wrong.

          The albedo of 1 Ceres is very dark, so the “white” spot might just be light gray or some other gray scale value that stands out against the more or less black surface of 1 Ceres. It’s fun to speculate…but there is more than enough data to move to informed speculation rather than what we’d like to see. Sure would be cool if there was a lot of water ice, but it doesn’t seem like that boat floats :)

          • Andrew R Brown says:

            Hi Matt, Marc and Sean,

            Loving the discussion on this blog.

            Yes, mineral reactions particularly between alkaline and acidic compounds may cause additional heating at the base of the likely ice rich mantle and rocky core, I still think 1 Ceres is currently inert, not necessarily always been so, but I think for at least 3 GY maybe more has been.

            I still suspect we will see little more than impact craters, but that is no bad thing in many respects, as that will record a history of the environment that the surface of the protoplanet has been exposed to, perhaps did 1 Ceres form in the Asteroid Belt close to the current orbit? Is 1 Ceres a KBO, a brethren of Eris, Pluto, Triton, etc and ended up in the Asteroid Belt, or is 1 Ceres a former moon of maybe Uranus or Neptune?

            The Framing Cameras will tell us the current geological condition of the surface and possible history, the GRaND may well reveal elemental makeups confirming or denying certain hypothesis. The VIR will certainly help with the surface properties.

            Will be interesting to see if 1 Ceres has any tiny moons or if the surface shows evidence of formers moon or moons that may have deorbited and impacted the surface? :D

            Andrew R Brown, Ashford, Kent, United Kingdom.

  31. Ferdinand Bénard says:

    Hello M. Rayman,
    thanks for your interesting and pleasant Dawn journal, congratulations to the Dawn team for their competence and for sharing the exploration of Céres, this new fascinating world, after a long cruise. Like many people, I’m curious and impatient to see the next images of RC1, and to learn more about the bright spots, the ratio of water ice and the possible seasonal “geysers” discovered by the Herschel team.
    Ferdinand from Reunion Island.

  32. Fabian P. says:

    What an intriguing mission!

    I have to admit, I haven’t heard about the Dawn mission up until somewhat recently. Now that should not hinder my excitement (although I can only imagine what it is like having worked on such a mission, anticipating the arrival for all those years and now seeing all that finally coming to fruition).

    Very interesting to see how different a mission with ion propulsion is compared to other missions. I’m curious to see what future missions will take advantage of this technology.

    I was also a little surprised at how close the spacecraft will eventually get to Ceres in its orbit. If I’m not mistaken it’s about as close or comparable to low Earth orbit. That seems pretty close to me. I’m sure it will provide a good look at Ceres.

    All in all, I think every new addition to the list of visited and explored objects in the Solar System is worth celebrating!

    Very excited to see what the next months will bring, thanks for making this possible!

    • Marc Rayman says:

      Thank you for your nice comment, Fabian. Yes, Dawn is quite an extraordinary mission. I appreciate your interest in it.

      You are quite right that our altitude above Ceres will be the same as that of many satellites in low Earth orbit. In its lowest orbit, the spacecraft will be about 230 miles (375 kilometers) above the surface of the alien world. That’s a bit lower than the International Space Station is above Earth. Dawn will operate there for months, and it should be fantastic.

      I’m sorry you weren’t onboard yet for the amazing adventure at Vesta, but when Dawn explored that giant protoplanet in 2011-2012, it spent five months at an altitude of 130 miles (210 kilometers). It acquired more than 13,000 photos, more than 2.6 million visible and infrared spectra, 91 days of accumulated gamma ray and neutron spectra, and 80 days of high precision gravity measurements. Along with the other phases of the Vesta mission, Dawn yielded an amazing portrait of a complex world that is more closely related to the terrestrial planets (including Earth) than to typical asteroids.

      I am confident dwarf planet Ceres will be at least as exciting, as fascinating, as rewarding as Vesta, and I am delighted you are now along to share in it!


      • Andrew R Brown says:

        Hi Marc,

        Any reason why DAWN’s LAMO at 1 Ceres is considerably higher than at 4 Vesta? Also will the cameras be carrying out ride along observations in LAMO alongside the GRaND?

        I assume a potential extended mission to closely encounter (not orbit) 2 Pallas in December 2018 is definitely out of question regarding the reaction wheel failures?

        Also I would have thought that pathetically weak Ion thruster would not make that much of a difference with the stability of the huge DAWN spacecraft as there are not major forces acting on the spacecraft causing spin? What gives?

        I am also looking forward to the observations of the space surrounding 1 Ceres looking for any tiny moons the protoplanet may have. I was not surprised that 4 Vesta was moonless, owing to the shape and mass distribution not being conducive to long term stable orbits, but then Main Belt Asteroid 243 Ida has the moon Dactyl, so I suppose anything maybe possible. 1 Ceres appears far more spherical that 4 Vesta and certainly much more so than 243 Ida, so moons are likely to be far more likely, unless it turns out 1 Ceres has significant MASCONs (MASs CONcentrations) like the Moon and recently discovered with Mercury.

        Andrew R Brown. Ashford, Kent, United Kingdom.

        • Marc Rayman says:

          Hi Andrew,

          All of the orbits at Ceres are at different altitudes from the orbits at Vesta. Ceres is significantly larger and the gravity field is different, so we use different orbits to explore it. I presented the plan for the low altitude mapping orbit (LAMO) here. Although the highest priority work there is collecting the gamma ray and neutron spectra and the gravity measurements, we do intend to use the camera (as well as the visible and infrared mapping spectrometer) for bonus observations.

          We have never considered a mission to visit Pallas, although I know that there have been rumors to the contrary. You can find some additional comments on our not going to Pallas by following the links here.

          I don’t understand what you are asking in the third paragraph. The spacecraft is designed to control its orientation with the wonderfully gentle ion thruster whenever it is thrusting.

          Thank you for your interest.


  33. Mark Gaponoff says:

    Kosmic Kudo’s to you and your team! This is very exciting!

    My speculation is that Ceres will turn out to be most like a mini-Callisto. We shall see!

    • Sean Deany says:

      Mark you are right about Ceres being a mini Calisto I have though so myself about this for some time. Perhaps Calisto, a former Kuiper belt object, was captured by Jupiter and Ceres a once wandering Kuiper belt object wandered to it main asteroid belt location – this is only theoretical and would not be regarded likely. A sample return missions to both worlds will possibly only prove this.

      • Mark Gaponoff says:

        Callisto and Ceres have similar densities, and seem to have existed their lifetimes without tidal disruption. Ceres is a bit denser, but also closer to the sun, and so may have lost some volatiles.
        Both bodies are crater saturated, with little evidence of tectonics or significant differentiation (Callisto’s greater mass may have generated more differentiation in its interior), and their composition is consistent with being formed near their present position, no need to invoke a Kuiper Belt origin.
        Gravity measurements when orbit is established will show if Ceres’ oblateness is evidence of some modest differentiation (or even if there is a well-buried internal ocean).
        It will be interesting to see if Ceres shows any of the sublimation erosion features that Callisto has.

  34. Tom Hopp says:

    Marc, I may have missed this among the many reports and comments, but could you tell us, is Ceres near equinox? Looking at the rotating images you posted on Feb 5, it looks like the south pole is just barely illuminated, suggesting Ceres is near equinox. I understand from a previous post that the direction of the axis is not precisely known, but it would appear that Ceres is near equinox and therefor well positioned to give us a view of most of the surface. Is that true?

    • Marc Rayman says:


      You’re right that the direction of Ceres’ axis is not precisely known (yet!), but it is tipped only a few degrees from the plane of its orbit. (This might help others understand a bit more about the axial tilt.) It seems to me then that in one practical (albeit unconventional) sense, Ceres is always near equinox. That is, the sun is always near the equator, so, yes indeed, most of the surface is lit during a Cerean day. That would also mean the poles are never more than “just barely illuminated.” Astronomers have several estimates of the pole location but using one popular one, a colleague calculated for me that the sun right now is about 4 degrees south latitude and near the southern summer solstice.

      I should add that Dawn is not over Ceres’ equator, so we are not seeing the northern and southern hemispheres equally. It is approaching over the southern hemisphere, and it was above (roughly) 22 degrees south latitude for OpNav 3. Dawn will cross the equator between RC1 and RC2.


      • Tom Hopp says:

        Thanks Marc. So, even though southern solstice ought to be the worst time to view the northern hemisphere, we’re in luck because polar darkness is never very extensive. I’m eager for RC2 and a peek over the top!

  35. Luis says:

    This is just a very preliminary perception on the surface features that so far are starting to be noticeable from Dawn’s imagery. I might be wrong, bu it looks like that the Southern hemisphere of the Planet is much more heavily crated then the North, and perhaps hinting to the fact that the Northern H. has been “more active”, in the recent geologic past, in planet owns dynamic events that have “retouched” out its surface landscapes. Bright spots might have a say later on this.

  36. Sean Deany says:

    Fascinating latest images Marc

    It appears to be focused on the Piazzi feature – white spot evident in your series of old Hubble pictures given. When comparing the series of six 2004 colour Hubble images, I have posted this montage on my web site, its becoming easier now for referencing to be made along with the latest Dawn images. Due to the distance Ceres is now from the sun Piazzi does indeed look less prominent when compared with those 2004 images. One interesting feature seen in the motion footage is a large heart shaped / dual basin in the southern hemisphere which I had vaguely detected in the colour 2004 Hubble images. While still all a bit sketchy this latest view on Ceres makes the mind speculate even more.

    I’m really looking forward to the RC1 – global survey as kilometers to the pixel is to increase by almost 100 percent from what we have now. I understand that after the RC1 the first colour images will be delivered.

    • Marc Rayman says:

      There is much to be fascinated by here, Sean!

      I know you know about this, but for other readers, I’ll clarify that Piazzi is the temporary designation for a feature on Ceres observed in telescopes. It is named for the astronomer who discovered the dwarf planet in 1801. Here is my overview of the history of Ceres’ discovery and its status as a planet for more than a generation, then an asteroid, and now a dwarf planet, each change reflecting an improvement in our scientific knowledge. As I also explained there, the official names for Ceres features will follow a theme, so the name Piazzi will not be used on Ceres for much longer.


    • hI Sean,
      I have analyzed very well all past and recent images of Ceres. The bright region of which mention is the Region A, is not ” Piazzi “.
      “Piazzi” crater is in the hemisphere still not seen by Dawn.
      The central peak of the Region A can ‘be just a plain material more clear, and more reflective, in contrast with the dark surface of Ceres.
      I hope more and more best images, soon

      • Hi Marc,
        1. You can confirm that the bright “Region-A” is not visible in this new image (05/02/15)? In this new image-Movie The bright “Region-A” appears in the last movie-frame, on the extremly left edge, Right?

        2. And you can confirm that the “Piazzi” crater is in the hemisphere not photographed by Dawn?
        According to my observations the feature called unofficially “Piazzi” matches at this feature in the Dark, you can see the crater edge:
        Mnay Thanks, Daniele

        • Marc Rayman says:

          Hi Daniele,

          What some astronomers call Region A goes right through our view in OpNav 3. Piazzi would be just on the edge at the end.


          • Sean Deany says:

            Marc and Daniele,

            Region A (so called from the 2013 Herschel water vapor global map or the mid two images in the 2004 colour Hubble photo) is the white spot we all were so intrigued over in OpNav 01 and 02. Your both correct as the so named Piazzi hasn’t featured yet. The OpNav 03 image is of the hemisphere west of Reg A and to my knowledge is the highest elevated areas on Ceres. Piazzi once visible in the RC1 global survey should be prominant as perhaps the largest if not brightest feature on Ceres.

            Concerning nomcluture I hope soon the IAU will start deciding naming prominent Ceres features. While you have explained to me alreadt Marc features will be named after Roman agricultural festivals etc surely the man Piazzi could at least have a region nominated. If Region A – a very geeky name indeed gets a name perhaps it can be called Proserpina (there is already an asteroid by this name) – but only if Ceres has two moons – Liber and Libera!

  37. Drue King says:

    In the new animation, for the first time, to me at least, the bright spot appears to be a large raised elevation area, like Olympus Mons on Mars. I don’t notice it as much on the static pictures or the gifs. But in the 3-d animation, with the darker area around the bright central area, it appears to be a peak of some type. Time will tell if I’m totally in the wrong. But I do love seeing new worlds.

  38. Romana Starfield says:

    Wow, I just looked at the latest pictures on the image gallery! I love the latest animation of the February 4th navigation images. We’re definitely beginning to see the larger ground features now. This is so cool. It is nice to have something very fascinating to look forward to every now and then as Dawn gets closer to Ceres. Thanks so much for the image gathering table too. It lets us know not only when the next images will be taken, but how much bigger they will be. Can’t wait till the images from the 12th come back.
    Thanks again for the blog.

  39. Matt Gibbons says:


    I’ve just done some searching for Ceres’ albedo and it appears to be a VERY dark object. A piece of charcoal shot in a dark room on black velvet brings to mind how challenging imaging is of such an object. Thankfully you don’t have to deal with high velocity imaging like New Horizons will when it flies by Pluto in July at a speed of approximately 31,000 mph! Tracking the object is critical for that mission, and very stressful for the team because they have one chance to get it right and if they fail there is no going back. Thankfully for them, Pluto is much brighter than Ceres. With the relative speed between Ceres and Dawn, imaging should be a piece of cake…dark chocolate sounds good.

    And a substantive question. Will Dawn enter equatorial orbit or polar orbit. Based on what I see in searching the Blog, it looks to be equatorial. I would guess the reason being that out of plane orbital maneuvers are too resource intensive. Will there be enough fuel left for shifting the orbit of Dawn toward the poles?


    • Marc Rayman says:


      I think dark chocolate sounds great. I love it! (But I also think that exploring Ceres will be even sweeter.)

      As I wrote below, Ceres reflects about nine percent of the sunlight. That is dark but by no means the darkest we have seen in the solar system. For example, comet nuclei generally are darker. Every mission is designed to deal with the light levels available. You’re right that the lower relative velocity makes taking pictures easier. Still, the greatest benefit of Dawn being in orbit is not the ease of photography but rather the opportunity to conduct an extended, in-depth exploration.

      For others, a polar orbit is what it sounds like — it goes over both poles. An equatorial orbit, as you might guess, does not. Dawn used polar orbits at Vesta and does so again at Ceres. It is the only way to see the entire surface. I have explained this in quite a few Dawn Journals, but one that might be particularly helpful is February 2014. (Another, perhaps with more detail than some would want, is May 2012.)

      Part of what makes this mission so powerful is that we can optimize the orbits to meet different scientific objectives. It is thanks to the maneuverability provided by the ion propulsion system that we can change the orbits so much. Changing orbits is generally very energetically expensive. It is more costly when orbiting a more massive body. Ceres is massive enough that it would be quite expensive without ion propulsion and with no large moons to use for gravitational bending of the trajectory. As I explained here, some of the ion thrusting after entering orbit around Ceres is used to tip the plane of the orbit to make it polar.


  40. phenporter says:

    I’m looking at the animated gif of the OpNav 3 images… Very cool surface renderings. My brain wants to trick me into believing that the relatively bright feature is looking elevated relative to its surroundings as the feature is approaching the right hand limb (near the end of the loop). Then I realized that those frames I am referring to are completely warped/generated based on images wrapped on a spherical surface rendering. Arrgh … but totally cool you can project and display in that manner. More bait to bring us back for more!

  41. Luis says:

    OpNav 3 images are here! One likely impact crater feature is now identifiable in the Southern Hemisphere of Ceres. “Snow White” looks like to be a complex and interesting feature. Each set of images brings a crescendo of new questions while at the same time the prior ones get bigger and bigger. “South Pole” has a rich topography, with dark patters that are yet to be determined. This is going to be a phenomenal diverse little world. How Exciting!!!


  42. Troy says:

    I’m wondering if Ceres is found to have a moon if this might change the current plan to end the mission in a parking orbit. A couple of things occurred to me, a moon might have potential for collision and it also might be possible to have a soft landing on a moon (which would have much less gravity than Ceres).
    I suspect it very unlikely at this point that there is a moon, but I know the Dawn team is still looking.

    • Marc Rayman says:

      This is an interesting question, Troy.

      Even if there is a moon, it is extremely unlikely to present a collision hazard. The volume of space around Ceres in which a moon could be is huge, and Dawn and a moon each would occupy a very, very tiny fraction of it.

      You’re right that the gravity probably would be low enough to land. With its giant solar arrays, however, landing would be awkward. This bird is meant to fly in space, not roost on the ground.

      For others, I described the planned end of the mission here. Going to the moon would have to be after the conclusion of the primary mission in June 2016. The primary mission objectives would be paramount. If NASA chose to invest additional resources in Dawn, I have to wonder whether the time spent maneuvering from that final orbit to rendezvous with a moon would be worth taking away from additional Ceres observations that we could otherwise make during that same time. In that low altitude orbit, the view will be fantastic. Even if we photographed the entire surface from there (which would be a bonus), I don’t believe we ever would run out of very valuable data to continue to collect with the four spectrometers (visible, infrared, gamma ray, and neutron). We would have to (get to!) judge the relative merits of visiting a small moon and performing the additional observations of Ceres. Until the moon is discovered, that’s a judgment I can’t make, but I’m doubtful it would prove worthwhile. Still, it’s an intriguing idea to consider.


  43. Paul Kuenstler says:

    Hi Marc,
    As always, your Journal and comments are really interesting.

    Given that the adjusted approach trajectory might be described as a little “loopy”, it might help to update the two trajectory figures (November Journal) to show locations for RC and OpNav imaging activities. That would be a nice complement to information you posted in the table of activities. Based on the March 5 “capture” point labeled in the figures, I think that RC1 would be the first imaging activity that would show up on the trajectory figure you included in this month’s Journal.


    • Marc Rayman says:

      Thank you, Paul. I appreciate your message.

      You are quite right that RC1 is the first imaging activity in the figure above. The previous ones occur off to the left. (In the second trajectory diagram in November, RC2 is the first.) I have indeed thought about including an illustration with the imaging sessions pointed out. It’s difficult to cover every aspect of the mission, but I will try to find the time to provide such a figure.

      In the meantime, other readers may want to take advantage of what you have already recognized. You can figure out where in the diagrams something is happening by starting with the capture as a reference. Using the white circles at one-day intervals, simply count forward or back to see where the spacecraft will be on other dates, including the ones in my table.


  44. Hello Marc
    The answers That you from for all of us, are very useful for
    not to write questions already asked.
    Will be a color images of Ceres in future?
    if you have already written in the past, I’m sorry, I always read everything I hope I have not missed look.
    What main color should be the Cererian Surfeces?
    Albedo of Ceres to those body of the Solar System (planet, asteroid, comet, moons) observed by mission is similar?
    Many many Thanks,

    • Marc Rayman says:

      Hi Daniele,

      We will take pictures with the camera’s seven color filters (in visible and near infrared) in RC1 and RC2. Overall, Ceres will not have a strong color and likely will look gray, but the subtle variations that the camera can detect will help scientists tease out clues about the composition of the surface. As we get closer, and the resolution improves, we may see more variation in the color in smaller regions. Dawn will take many color pictures later, and in the second lowest orbit (misleadingly called HAMO), it will map the entire surface in color.

      Thank you for following the mission so carefully!


  45. Roshan Jagtap says:

    Hello Marc,

    This really adventures. Thanks you are sharing this info with all. I am very curies with planet Ceres, Looking forward more images specially want to know about foggy layer all over Ceres Surface in early images.

    I have question for you what gone happen to Dawn spacecraft after Ceres objectives?


    • Marc Rayman says:

      Hi Roshan,

      I’m glad you are participating in the adventure. And that adventure will end in Dawn’s lowest orbit at Ceres, at about the same altitude above the alien surface as the International Space Station is above our home planet. I described our faithful spacecraft’s fate here.


      • Roshan Jagtap says:

        Hi Marc,

        Thanks for reply.
        I am curies about what are your opinion, As mission Director you are the most closet person to this mission what are your opinion about Ceres surface and all possibility on Ceres, What that white spot could be? I am sure you have build your own thoughts too on this after watching latest image. :)

        You are doing Great work Man!!!


  46. Mewo says:

    So, by now the next set of images will probably have been taken, showing Ceres in ~70 pixel glory. I can’t wait to see them. Is it sad that checking this site has become part of my morning routine? Nahh…

    • Marc Rayman says:

      Hi Mewo,

      The pictures should have been taken, and I too can’t wait to see them. But I will wait. Even now (the morning of Feb. 4), it is not yet time for Dawn to communicate with us. It is still engaged in other tasks.


      • Mewo says:

        Wow, the new images are stunning! I see a big impact crater near the bottom with a central peak, but aside from that Ceres is apparently much smoother than I expected.

  47. David Kenney says:

    Dr Rayman,

    Like everyone here, I’m on the edge of my seat waiting for new images from Dawn to bring Ceres further into focus (as I was when Vesta images started coming in). Basically, I’m looking for a schedule listing when (assuming all goes well) the public can expect access to new Ceres images. The table here is some help. Can we expect a new images within a day of the dates listed here?

    Knowing when to look for images would save me from checking every few hours. (Am I the only one that does this.)

    • Marc Rayman says:

      I understand your eagerness, David, and I appreciate your enthusiasm! You won’t have to wait much longer for the OpNav 3 images.

      After receiving the data, the team has to process the images before making them public, following established processes. We post the pictures on this website and elsewhere as soon as those processes are complete, but I don’t know how long that will take for each activity.


  48. Marc,

    Such a neat story! At the end of my scientific career as a marine biologist, I realise that well upon 50 years ago when I was making choices for grad school I made the wrong ones.

    What grandeur and awesome magnificence you folks deal with on a daily basis! I should think, at times you and your team, would find it hard to “return to earth” for normal discussions and conversations.

    With all of hardware on the probe that must function properly to assure mission completion – for example the reaction wheels – I am a little surprised that there were not back-up plans in place for failures. It appears as if you guys worked everything out, but it would have been more efficient, I suspect, had you just been able to say, “Reaction Wheel A is not responding; time to go to plan B.”

    What a nice narrative, thanks!!! Ron Shimek

    • Marc Rayman says:

      Thank you for your kind comment, Ron.

      Fortunately, you got to have a rewarding scientific career in an important and fascinating field, and now you get to share in the Dawn mission’s extraordinary adventure. Welcome aboard!

      Each member of the team experiences the wonders of this mission differently, not only in degree but also in character. I’m sure there are some who, like me, are deeply moved by controlling a spacecraft to explore an alien world well over one thousand times farther from Earth than the moon. (I also happen to enjoy expressing my feelings about it and trying to engage the rest of the world.) Others find the greatest rewards of their work in details of their technical specialty with less interest in the context of the overall mission. That’s fine. Together, we have very effective normal discussions!

      We most certainly have back-up plans in place for failures. Dawn carries an extra of virtually everything it physically could. We need only one radio transmitter, but we have two. We need only one radio receiver, but we have two. We need only one main computer, but we have two. We need only two ion engines, but we have three. We need only eight sun sensors, but we have 16. The list goes on and on and on, and I could suggest many links to previous Dawn Journals that give details. (We also have many kinds of back-up plans for problems other than hardware failures. As just one of many examples, we plan to collect more data at Ceres than we need, with the full recognition that some problem, which we do not specifically anticipate, will interfere with some of the observations.)

      We needed only three reaction wheels, so we have four. When the first reaction wheel failed, we went to our back-up plan, which was to use the other wheels. But we immediately started developing a new back-up plan, which included developing a new capability to operate with only two wheels (“hybrid control“), conserving hydrazine and extending the life of the remaining three wheels. (This is described in many previous Dawn Journals. You could follow some of the links in my text above. You could also start way back here.) All of those paid off very handsomely. Had we not preserved the wheels in 2010 and 2011, for example, the second wheel likely would have failed so early at Vesta that we would have expended too much hydrazine to be able to complete the Ceres mission.

      It is thanks to such careful thinking and preparation that space missions are so successful. And now we are about to reap the rewards of that work on Dawn.

      It’s good to have you along!

      Finally, I can’t resist pointing out that, based on some of what I have described about Ceres, we might fantasize about whether marine biologists might be needed for futuristic missions there :-)


      • Ronald Shimek says:

        Hi Mark,

        Thanks for the explanation!

        Believe me in another life I would love to marine biologist on exploratory missions such as this.

        One final comment, as I thought about this mission, it struck that with the ion propulsion, and dynamic rather constant changes you folks are making, in a way, you are a lot like the first mariners who set sail from an uncharted shore millennia ago, striking off in search who knows what, riches, spices, survival.

        Wonderful story!!

  49. Luis says:

    These are very interesting times indeed!

    Looking at the animation depicting the last data coming from Dawn, it seems that there are 3 more “white” features to the east of “Snow White”, in the Northern Hemisphere of Ceres. “Snow White”, seems to be a “static” geomorphological feature (likely an impact crater, and relatively young, with exposed “fresh” material – perhaps Ice??). The new batch of imagery will certainly bring a little more light on these, and more.

    Thanks for sharing!

    • Marc Rayman says:

      Thank you for your interest, Luis! I share so that you can know how interesting these times really are.

      I agree that the bright spot does indeed appear to be static in that it has been observed since Hubble’s pictures from more than a decade ago. As I wrote in the comment immediately below, however, I do not believe it is an indication of fresh ice.


  50. Andrew BROOKS says:

    Dear Marc,

    I often thought that ‘Great White Spot’ is where water jets or sprays comes out (for few days only) each time when Ceres is closest to the Sun. Now Ceres is now moving further away from the Sun and this spot is white all over again with frozen ice. A bit like a ice volcano and dormant 99.5% of the time.

    I am looking very forward to find out if this assumption is correct or not in the next few months!

    Cheers Andrew

    • Marc Rayman says:

      Hi Andrew,

      I do not think the bright spot is exposed ice. Ice on the surface would sublimate, producing water vapor in the space above Ceres. As I reminded Matt in the comment immediately below, Herschel observed water vapor, but in a tiny amount. Explaining the Herschel findings with ice sublimation would require only about 0.2 square miles (0.6 square kilometers) of exposed ice. That is equivalent to a square about half a mile (three-quarters of a kilometer) on a side. Compare that to the pixel sizes in my table above. The bright spot seems to be too large to fit with the minuscule amount of water vapor.

      I share your eagerness to find out what it really happening on Ceres. I’m glad you’re going to share in the discoveries!


      • Matt Gibbons says:


        The white spot has my attention…if it can’t be water ice, then are we talking about hydrocarbons? Complex organic compounds? What are the basic constituents of Ceres?

        Nitrogen came to mind, but to be in a liquid state it needs to be about 100 degrees K colder than the temperature on the surface of Ceres. Carbon dioxide ice (dry ice) perhaps? CO2 sublimates to a solid at 194 deg K, which is within the temperature range of Ceres (168-235 deg K), correct?

        One last couple of sentences…is the “white” spot really white, or is it an albedo feature, i.e. a relatively bright spot against an otherwise dark surface? Is Ceres a very dark object?

        Thanks for you time Marc!


        • Marc Rayman says:

          Hi Matt,

          As I mentioned below, we don’t know the constituents of Ceres well enough to say what the bright spot is.

          I don’t know what the bright spot is, and I think it’s too soon to call it white. It is visibly brighter than the rest of Ceres. Ceres generally reflects about nine percent of the sunlight. When we get close enough to see what the size of the “spot” is, then we will be able to say how much more reflective it is than the other terrain. Is it very small and very reflective, or larger and not quite as reflective? We’ll all find out soon!


          • Matt Gibbons says:

            This is obviously not a horse race, but I’m still betting on CO2 snow or ice as the basis for the great small white spot…based on the (reported) temperature at the surface of Ceres. It’s all just speculation, but that is what makes it so exciting, trying to figure out what an object is at a distance with the sure knowledge that a magnificent reveal is just about to happen.

  51. Matt Gibbons says:

    Hello again Marc…keepin’ it short is the soul of discretion!

    In watching the animation there appears to be a canyon, or series of canyons, possibly peppered with impact craters, girdling the southern hemisphere. It reminds me (and perhaps this is just my imagination at work) of Ithaca Chasma on Saturn’s moon Tethys. There is definite relief in the southern hemisphere, but the low resolution makes it difficult to determine precisely what it is. Same goes for the white spot…maybe a cryo volcano?

    Care to speculate? I know…it’s too early to say, but what the heck…go for it! ;)

    Looking forward to tomorrow…new photos, yes?


    • Marc Rayman says:

      Hi Matt,

      I’ll be brief (for me) too. As I have written before, including in the comment below, I am confident we are not seeing a cryovolcano in action now. I explained in December that the Herschel Space Observatory detected a very, very small amount of water. If there were a cryovolcano large enough to show up in these early images (and the ones taken by Hubble a decade ago), Herschel would have found much more water.

      You mentioned looking forward to new photos “tomorrow,” meaning Feb. 3. I look forward to them too!! Perhaps I should clarify that my table above gives the day we start an activity. Keep in mind that that is not when the photos are available but rather when Dawn begins acquiring them. For example, in OpNav 3 it takes pictures of Ceres for three hours starting shortly before midnight tonight (Feb.3), and after that it spends another 3.5 hours searching for moons. (More properly, it takes pictures that scientists will spend a tremendous amount of time analyzing for the presences of moons.) After the spacecraft finishes its observations, it takes many hours (usually more than half a day) to transmit its findings. The first bits from OpNav 3 won’t reach our planet until well into Feb. 4 PST. The team then will process the data into photos before making them public, following established processes.


  52. phenporter says:

    I like all the white spot speculation! Certainly it is the only readily discernible “feature” so that’s what we are talking about now, but I fully expect that it may in the end be easily explainable and not even close to being the most exciting of the discoveries to be made. Nonetheless, Marc, its fun to speculate!

    I would not be so inclined to dismiss the geyser hypothesis. While there may not currently be a massive active geyser and accompanying Ceres-cumulus clouds, what would we expect to see as evidence of past activity? Maybe a salt cone, salt pan or salt glacier; snowed out minerals from many thousands of previous eruptions? Imagine “Old Salty” with a period of many years. My favorite notion, however, is a crater with a salt pan floor fed by many impact shock induced fissures, seeps, and/or seasonal flows bleeding out and evaporating the ocean within.

    • Marc Rayman says:

      I agree it is fun to speculate, Stephen. I do so also. I just don’t speculate well enough to warrant doing it out loud all that much :-) Also, to ensure that we continue to get better and better photos and other data at Ceres, I need to devote a great deal of time to conducting the mission. I love sharing this amazing adventure with you and others. Much as I would enjoy (some aspects of) engaging in speculation here and writing even more than I do, my time is very limited.

      I was not dismissing past activity as an explanation for the white spot. (I don’t call it a white spot but rather a bright spot; we haven’t taken color pictures yet.) I do not believe we are seeing a geyser in action now. I interpreted the other comments to be referring to present activity, but that may have been my misunderstanding.

      Certainly you are right that the spot may be a result of some past activity, and your suggestions are good ones. If I spend my time judiciously, then Dawn will provide us with exciting, higher resolution photographs and spectra (which reveal the composition and other properties of the surface material). That should tell us much more about what the nature of the bright spot is, whether it is one of the possibilities you propose or something else. It is fun to speculate, and it will be even more fun to know what Ceres says about it!

      Thank you for your ideas.


  53. Mewo says:

    Hi Marc,
    excellent writeup once again. I’m eager to know exactly what that white dot is. It seems to only be about a pixel across, or less, which is smaller than I expected. Yet it’s bright enough to be clearly visible to Hubble. Whatever it is, it must be remarkable.

    • Marc Rayman says:

      Thank you, Mewo.

      I am looking forward to many remarkable discoveries at Ceres. I agree that the nature of the (relatively) bright dot surely will be one of them. It may well be that the most amazing discoveries will be about features we don’t even have hints of yet. This is going to be really exciting!


  54. Joakim Rosqvist says:

    Given the enormous challenges of getting a spacecraft mission to work: stresses on launch, varying pressure and temperature, radiation, micrometeorites, … it seems odd to me that spinning a wheel reliably is the problem engineers can’t solve.
    Even the mighty Hubble mission is supposed to end when it has too few wheels left.
    I’m glad you managed to figure out how to let hydrazine do the job instead but what is it about reaction wheels that make them so prone to failure?

    • Marc Rayman says:

      Hi Joakim,

      You touched on part of the answer in the beginning of your comment. The wheels have to survive the stresses of launch and yet still spin flawlessly for years and years, over many billions of revolutions, under all the hostile conditions of spaceflight. That is not easy, and it is quite difficult to test here on Earth to ensure a high rate of success for a long mission in space. Nevertheless, the vast majority of reaction wheels have worked exceptionally well on spacecraft.

      I suspect that reaction wheel failures may have received public attention recently that is out of proportion to the magnitude of the problem. Of course, it is very important for any mission that experiences a reaction wheel problem, as Dawn has, but most missions have no such problems! The devices are not, in general, prone to failure, but they may be prone to news of failures.

      The exploration of the cosmos is extremely challenging, and sometimes a design proves not to be as effective as predicted. As I commented last month, engineers do have other reaction wheel designs however that are recognized to be reliable. I think it is actually quite remarkable that spacecraft work as well as they do!


  55. Sean Deany says:

    Hi Marc

    Concerning moons of Ceres. I’m making a wildly hypothetical prediction here as a lay person and basing it on the two moons of Mars (in its relation of mass to Ceres) – Phobos (mean radius 11.2 km or 1/302.63 Mars radius) and Deimos (mean radius 6.2 km or 1/546.69 Mars radius) as my scenario basis. Assuming that 1 Ceres has two notable moons – Liber and Libera, they being captured C type asteroids and / or rubble piles. They would have a mean radius of: Liber – 1.57 km and Libera 0.87 km. Therefore Liber should be detected by DAWN’s camera prior to OpNav06 and Libera should be detected after OpNav07!

    • Marc Rayman says:

      Hi Sean,

      It’s interesting to use Mars as a basis for your scenario. That’s clever. I should point out that Phobos and Deimos are believed to be captured asteroids and not in any way connected with what size Mars is. (Jupiter has also captured asteroids, and their sizes in comparison to the giant planet are very different form those of the Martian moons.) Mars could have captured larger or smaller asteroids. In fact, I would have to wonder how Ceres would “know” to capture asteroids as moons that are in proportion to whatever happened to wander close enough to Mars to get trapped in orbit.

      Also note that for Dawn’s camera to detect a moon, it doesn’t necessarily have to be one pixel in size. If these are captured asteroids, they could be more or less reflective than Ceres itself. (For our moon search analyses, we assume equal reflectivity.) Depending on how bright a moon is, it might be visible if it’s smaller than a pixel, because it still provides enough light to show up. (Remember, stars are visible, and they appear much, much smaller than a pixel.) If it’s darker, it may simply not show up. Now it’s actually more complicated than that, because a moon of Ceres, depending on what orbit it’s in, could move during the exposure. If it does, then it would be smeared across multiple pixels and hence be dimmer.

      So, predictions about the presence of moons and their detection are fraught with complexity and uncertainty. Of course, much of the attraction is that we don’t know! Maybe you will be right after all. Nature will have the final word, and it will be wonderful to find out!


    • Hi Sean,
      I really like your hypothesis moons size, I had made a report of moons very similar to yours; I hope at least a one moon is discoverd..
      Thanks to Marc rayman for the answer.
      Daniele Bianchino,

      • Sean Deany says:

        Hi Daniele,

        I’m hoping on at least one moon to be discovered by DAWN – but its going to be very small. My estimates above were perhaps more optimistic and purely hypothetical. If there are moons of Ceres they will be not much more than small rubble piles / captured asteroids. Its the white spots on Ceres, as the Piazzi region I believe will be more prominent than the one we have so far seen at Region A.

  56. Kamal Lodaya says:

    A question regarding the relative position of comet C-G/67P: when did/does it cross Ceres’s orbit and Vesta’s? Since Ceres is about 400 million km from the Sun, Vesta is 350 million km and the comet is around 360 million km from the Sun it should presently be between the two orbits. Is there a chance that Dawn can get a decent picture of the comet?

    Your response: The comet is so small that even if it were on Ceres right now, it would be too small for Dawn to see!

    Question again: I did not mean the nucleus but the coma and the tail. I guess it is not possible for Dawn to long exposures of deep sky objects.

    • Marc Rayman says:

      Hi Kamal,

      You and I had a brief email exchange outside the blog, but I’ll try to give a complete answer here for everyone else’s benefit.

      The comet you refer to, Churyumov-Gerasimenko, is where the wonderful Rosetta mission is right now.

      The solar system is really big, so crossing the orbit of another body says very little about being close to it. If you are traveling around Earth’s equator (as an analog of orbiting around the sun), and I am going from pole to pole, I might cross the equator (your orbit) in Ecuador when you happen to be in the Atlantic Ocean. We would be very far apart.

      It’s actually more complicated than that, because the orbits are of different sizes and shapes, so in general they do not intersect at all. Still, one of my busy colleagues on the Dawn navigation team kindly contributed some analysis to try to answer the intent of your question.

      The comet doesn’t really cross the orbits, but it will be at the same distance from the sun as Vesta on Feb. 28. As I mentioned in my blog above, Dawn is already farther from Vesta than Earth is from the sun.

      Dawn is close enough to Ceres, that for our purposes here, we can treat them as being at the same place on the scale of the vast solar system. On Dec. 10, 2014, the comet and Ceres (and so the comet and Dawn) were at the same distance from the sun (both 2.80 AU). That might seem like an opportune time for our spacecraft to peer at the comet. Yet they were 2.38 AU apart (260 million miles, or 418 million kilometers). This is analogous to the two of us being on the equator but 50 degrees apart in longitude.

      We found when Dawn would be closest to the comet, which is more to the point. By a fun coincidence, that happens to be today! (I hope you’re enjoying it.) Still, Dawn is 2.28 AU (212 million miles, or 341 million kilometers) from the comet. As I have written in many of my Dawn Journals, our camera and spectrometers were designed for studying the solid surfaces of bodies from orbit. At well over twice the Earth-sun distance, this would not be a productive observation. There are, of course, many other comets as well. And Dawn could take pictures with long exposures if there were a good reason, but in all cases, the most effective use of this sophisticated robot is to observe Vesta and Ceres. (Following the loss of the second reaction wheel, which made hydrazine such a precious resource, this became even more true.)

      Although you knew that the nucleus is too small to observe, some may not realize that. Typical cometary nuclei are no more than a few miles (kilometers) across. (I was lucky enough to be responsible for NASA’s first close-up pictures of a comet with Deep Space 1, an exciting event I described here.) As I wrote last month, Ceres’ equatorial diameter is about 605 miles (975 kilometers). If the comet were at the same distance from Dawn that Ceres was in OpNav 2, it would not even have shown up! It is so small that it would not even stretch across two pixels until OpNav 4. Dawn is designed to explore giant worlds. That is what it did at Vesta, and that is what we are about to do again!

      I hope this answers your question.


  57. Chris S says:

    Ceres looks amazing already. 2015 is going to be a fantastic year.

    I have to say, though, I imagined a beautiful crescent Ceres as you mentioned it, and then was a little saddened when you subsequently said that you couldn’t point the cameras so near the sun at that spectacle. Will there be safe times to look at a crescent Ceres?

    Thanks again for these updates! I was excited for this blog entry, knowing that in next month’s we’ll pretty much be There.

    • Marc Rayman says:

      Thank you for your interest, Chris.

      I couldn’t agree more with your first three sentences.

      You needn’t be sad! As you can see from the table, the OpNav 5 and OpNav 6 pictures will show crescents, with less than one quarter of the disk lit. I think Ceres will be quite photogenic indeed. Perhaps my journal explanation wasn’t clear. My point was that we would not take pictures when the crescent was even narrower than 18% illumination.

      By the way, the crescent moon on Feb. 15 will be comparable to the shape Ceres will display in OpNav 6. You can see the moon from early morning to early afternoon that day (although I don’t make predictions about cloudiness).

      We have much to look forward to!


  58. Guillaume Vollant-Boulé says:

    Hi Marc,
    Great blog as always. Do we know why ceres is such a dark planet compared to Vesta and other objects in the solar system from the data we have now? Merci and good luck!!!

    Guillaume Vollant-Boulé

    • Marc Rayman says:

      Thank you, Guillaume.

      Despite fine work to determine the nature of Ceres, we still don’t know what the composition or structure of the surface is. There are different ideas, some of which have to do with past interactions with water or sublimation of ice, but right now, there are more questions than answers.


  59. Dawid says:

    Great post! Well written and full of info. Table is the best. As for the mysterious ‘white spot’, this is the same as ‘region A’ sensu Kuppers et al. 2014 (Nature), right? Then, I vote for giant cloudy geiser, Ceres being further example of a ‘missing link’ between asteroids and dwarf planets. I have a name for the feaure! Snow White must it be! :)

    • Marc Rayman says:

      Thank you, Dawid.

      For others, “Kuppers et al. 2014 (Nature)” refers to the scientific publication of the fascinating discovery of that exceedingly thin veil of water vapor around Ceres, as I described here.

      You are quite correct that the bright spot in our pictures is one of the regions those scientists offered as a possible source of the water vapor. But that possibility is based on Hubble’s very fuzzy views of Ceres, so it certainly is too soon to know if it really is the source. I like your idea, but I am afraid a more detailed consideration suggests it is not a cloudy geyser. A geyser (or even a cloud) large enough to be visible in these pictures would contain far, far more water than was observed in that very tenuous veil.

      I love your proposed name for the spot. Alas, an area of ice (or snow) even close in size to the spot also would produce much too much water vapor by sublimation to be consistent with observations. I think we have to accept that it remains a mystery. Or, to put it better, we are lucky enough to have a cool mystery!

      I’m not sure I’d say Ceres is a missing link between asteroids and dwarf planets. First of all, it isn’t missing; we’ve known about it longer than any regular asteroid and any other dwarf planet, and thanks to OpNavs, we know right where it is :-) And I wouldn’t call it a link either. It is quite unlike the asteroids, but it is a dwarf planet, meeting the definition of that term (whether one likes the definition or not) just as well as the other dwarf planets. What its real nature is we are about to discover!


  60. Hello Marc,Very good this explanation, especially various future images description(Km per pixel, Illuminated portion of disk and distances)..
    1. Some time ago I read that Vesta has probably a small moon, also a likely name; This was written by you in dawn blog journal, several years ago;
    was then confirmed this hypothesis? I think not;

    2. Now, Do you believe there are possibilities’ of Lune around Ceres? I believe that the first two fabolous images have shown that does not exist for now a moon noteworthy, if this existed ..

    3.The first characteristics of Ceres, I have noticed these:

    I think that the “bright eye” of Ceres is the peak of a central crater similar to those of the moon Umbriel of Uranus, as Wunda crater or Vuver crater; the bright area might be a central peack of different material expelled from the mantle of Ceres;
    We all loved the last image, more and more ‘, and beyond …
    Daniele Bianchino,- Italy

    • Marc Rayman says:

      Hi Daniele,

      I’m pleased you found this helpful. Though I have very limited time, I want to do what I can to let everyone be engaged in this adventure!

      1. Dawn searched for moons around Vesta but found none. I think you are referring to the ending of this Dawn Journal, in which I wrote about a Vestan moon and its name. Note that the principal topic then was that Dawn had entered orbit around Vesta. (Spoiler alert: I may make a similar statement about a moon of Ceres in a Dawn Journal in March.)

      2. It certainly is possible that Ceres has moons. You and I both posted comments about this in November, and I posted another earlier this month. Searches with telescopes would not have found a moon smaller than about a mile (one to two kilometers) in diameter. It is still too soon to know whether Dawn will discover one smaller than that.

      Thank you for your continuing interest!


  61. Maxwell Johnson says:

    Are there any notable features on the surface we can delineate based on what we have seen so far, including the “Great White Dot”? From the January 13th and 25th images they both appear they where taken at the exact same time in relation to the rotation of Ceres, is there a reason behind that? Also, thanks for the blog’s they’re very informative, can’t wait until we find out more!!!

    • Marc Rayman says:

      I’m glad you find my blogs helpful, Maxwell. Thank you.

      While the images are certainly suggestive of certain kinds of features, it’s really too early to say what they are. We see what appear to be craters, but it’s pretty difficult to say much more than that. My experience is that greater detail often shows that early guesses are wrong or, at least, naive. Some people may be good at those guesses, but I’m not, so I don’t speculate (out loud, anyway) anymore.

      It turns out to be coincidence that the pictures are at the same time in Ceres’ rotation, but there is a possibly interesting (and definitely long) story here. The basis upon which we choose the rough time for an OpNav is when we need updated navigational information for our scheduled trajectory refinements. That narrows the time down to about a day, so you’d think we still have plenty of flexibility given that Ceres completes a rotation in nine hours. However, we have other constraints, the principal one being the conservation of hydrazine. Dawn expends more hydrazine when it is coasting than when it is thrusting with the ion propulsion system, so we don’t want it to coast unless there’s a good reason. It is most efficient to pause ion thrusting, then take pictures, then transmit them to Earth, then resume thrusting, with no unnecessary gaps.

      This is a very busy time for NASA’s fabulous Deep Space Network, which is Earth’s link to Dawn and other interplanetary missions. There are DSN facilities in California, near Madrid, Spain and near Canberra, Australia. As different spacecraft are on their own independent routes through the solar system, they can sometimes be aligned so that many of them are simultaneously in view of the same DSN complex. That makes scheduling the use of these remarkable antennas more complicated. That happens to be the case now, so Dawn and all the other missions that appear in the same general region of the sky work together with the DSN in an impressively collaborative way. To be a good citizen of the DSN, I requested only that we receive tracking sometime within the window needed for receiving OpNav data. That allowed the most flexibility for the scheduling process. Once we jointly establish the exact time for Dawn’s use of the antenna, we work backwards from that to determine when to photograph Ceres so that the spacecraft uses its own time (and hence its hydrazine) as efficiently as possible. That led to the coincidence in the timing of OpNav 1 relative to OpNav 2. I hope that quick explanation makes sense.