Marc Rayman
Marc Rayman
Chief Engineer/ Mission Director, JPL
Dawn Journal | February 25

by Marc Rayman


Dear Fine and Dawndy Readers,

The Dawn spacecraft is performing flawlessly as it conducts the first exploration of the first dwarf planet. Each new picture of Ceres reveals exciting and surprising new details about a fascinating and enigmatic orb that has been glimpsed only as a smudge of light for more than two centuries. And yet as that fuzzy little blob comes into sharper focus, it seems to grow only more perplexing.

Dawn is showing us exotic scenery on a world that dates back to the dawn of the solar system, more than 4.5 billion years ago. Craters large and small remind us that Ceres lives in the rough and tumble environment of the main asteroid belt between Mars and Jupiter, and collectively they will help scientists develop a deeper understanding of the history and nature not only of Ceres itself but also of the solar system.

Ceres Op Nav 3 animated gif

Dawn observed Ceres for three hours, or one-third of a Cerean day, on Feb. 3-4. The spacecraft was 91,000 miles (146,000 kilometers) from the dwarf planet in this imaging session, known as OpNav 3. More detail on that one big bright spot is shown in another image below. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

Even as we discover more about Ceres, some mysteries only deepen. It certainly does not require sophisticated scientific insight to be captivated by the bright spots. What are they? At this point, the clearest answer is that the answer is unknown. One of the great rewards of exploring the cosmos is uncovering new questions, and this one captures the imagination of everyone who gazes at the pictures sent back from deep space.

Other intriguing features newly visible on the unfamiliar landscape further assure us that there will be much more to see and to learn — and probably much more to puzzle over — when Dawn flies in closer and acquires new photographs and myriad other measurements. Over the course of this year, as the spacecraft spirals to lower and lower orbits, the view will continue to improve. In the lowest orbit, the pictures will display detail well over one hundred times finer than the RC2 pictures returned a few days ago (and shown below). Right now, however, Dawn is not getting closer to Ceres. On course and on schedule for entering orbit on March 6, Earth’s robotic ambassador is slowly separating from its destination.

“Slowly” is the key. Dawn is in the vicinity of Ceres and is not leaving. The adventurer has traveled more than 900 million miles (1.5 billion kilometers) since departing from Vesta in 2012, devoting most of the time to using its advanced ion propulsion system to reshape its orbit around the sun to match Ceres’ orbit. Now that their paths are so similar, the spacecraft is receding from the massive behemoth at the leisurely pace of about 35 mph (55 kilometers per hour), even as they race around the sun together at 38,700 mph (62,300 kilometers per hour). The probe is expertly flying an intricate course that would be the envy of any hotshot spaceship pilot. To reach its first observational orbit — a circular path from pole to pole and back at an altitude of 8,400 miles (13,500 kilometers) — Dawn is now taking advantage not only of ion propulsion but also the gravity of Ceres.

On Feb. 23, the spacecraft was at its closest to Ceres yet, only 24,000 miles (less than 39,000 kilometers), or one-tenth of the separation between Earth and the moon. Momentum will carry it farther away for a while, so as it performs the complex cosmic choreography, Dawn will not come this close to its permanent partner again for six weeks. Well before then, it will be taken firmly and forever into Ceres’ gentle gravitational hold.

The photographs Dawn takes during this approach phase serve several purposes. Besides fueling the fires of curiosity that burn within everyone who looks to the night sky in wonder or who longs to share in the discoveries of celestial secrets, the images are vital to engineers and scientists as they prepare for the next phase of exploration.

These two views of Ceres were acquired by NASA's Dawn spacecraft on Feb. 12, 2015

Dawn acquired these two pictures of Ceres on Feb. 12 at a distance of 52,000 miles (83,000 kilometers) during the first “rotation characterization,” or RC1. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA


These two views of Ceres were acquired by NASA's Dawn spacecraft on Feb. 12, 2015

Dawn acquired these two pictures of Ceres on Feb. 19 at a distance of 28,000 miles (46,000 kilometers) in RC2. Dawn’s trajectory took it north between RC1 and RC2, so the terrain within view of its camera is farther north here than in RC1. The angle of the sunlight is different as well. Nevertheless, each of these two perspectives is close in longitude to the two above, so some features apparent here are also visible in the RC1 photos. The careful observer will note that these pictures are very cool, especially when compared with earlier ones from Dawn and the best from Hubble Space Telescope, as shown in last month’s Dawn Journal. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

The primary purpose of the pictures is for “optical navigation” (OpNav), to ensure the ship accurately sails to its planned orbital port. Dawn is the first spacecraft to fly into orbit around a massive solar system world that had not previously been visited by a spacecraft. Just as when it reached its first deep-space target, the fascinating protoplanet Vesta, mission controllers have to discover the nature of the destination as they proceed. They bootstrap their way in, measuring many characteristics with increasing accuracy as they go, including its location, its mass and the direction of its rotation axis.

Let’s consider this last parameter. Think of a spinning ball. (If the ball is large enough, you could call it a planet.) It turns around an axis, and the two ends of the axis are the north and south poles. The precise direction of the axis is important for our mission because in each of the four observation orbits (previews of which were presented in February, May, June and August), the spacecraft needs to fly over the poles. Polar orbits ensure that as Dawn loops around, and Ceres rotates beneath it every nine hours, the explorer eventually will have the opportunity to see the entire surface. Therefore, the team needs to establish the location of the rotation axis to navigate to the desired orbit.


Dawn took this picture in RC2. The improved resolution shows that the intriguing bright spot from earlier pictures is actually two bright spots. What a wonderful mystery this is!

We can imagine extending the rotation axis far outside the ball, even all the way to the stars. Current residents of Earth, for example, know that their planet’s north pole happens to point very close to a star appropriately named Polaris (or the North Star), part of an asterism known as the Little Dipper in the constellation Ursa Minor (the Little Bear). The south pole, of course, points in exactly the opposite direction, to the constellation Octans (the Octant), but is not aligned with any salient star.

With their measurements of how Ceres rotates, the team is zeroing in on the orientation of its poles. We now know that residents of (and, for that mater, visitors to) the northern hemisphere there would see the pole pointing toward an unremarkable region of the sky in Draco (the Dragon). Those in the southern hemisphere would note the pole pointing toward a similarly unimpressive part of Volans (the Flying Fish). (How appropriate it is that that pole is directed toward a constellation with that name will be known only after scientists advance their understanding of the possibility of a subsurface ocean at Ceres.)

The orientation of Ceres’ axis proves convenient for Dawn’s exploration. Earthlings are familiar with the consequences of their planet’s axis being tilted by about 23 degrees. Seasons are caused by the annual motion of the sun between 23 degrees north latitude and 23 degrees south. A large area around each pole remains in the dark during winter. Vesta’s axis is tipped 27 degrees, and when Dawn arrived, the high northern latitudes were not illuminated by the sun. The probe took advantage of its extraordinary maneuverability to fly to a special mapping orbit late in its residence there, after the sun had shifted north. That will not be necessary at Ceres. That world’s axis is tipped at a much smaller angle, so throughout a Cerean year (lasting 4.6 Earth years), the sun stays between 4 degrees north latitude and 4 degrees south. Seasons are much less dramatic. Among Dawn’s many objectives is to photograph Ceres. Because the sun is always near the equator, the illumination near the poles will change little. It is near the beginning of southern hemisphere winter on Ceres now, but the region around the south pole hidden in hibernal darkness is tiny. Except for possible shadowing by local variations in topography (as in deep craters), well over 99 percent of the dwarf planet’s terrain will be exposed to sunlight each day.

Guiding Dawn from afar, the operations team incorporates the new information about Ceres into occasional updates to the flight plan, providing the spacecraft with new instructions on the exact direction and throttle level to use for the ion engine. As they do so, subtle aspects of the trajectory change. Last month we described the details of the plan for observing Ceres throughout the four-month approach phase and predicted that some of the numbers could change slightly. So, careful readers, for your convenience, here is the table from January, now with minor updates.

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
122 4.9
3.8 98% RC1
Feb 19 28,000
222 2.7
7.0 87% RC2
Feb 25 25,000
255 2.3
8.0 44% OpNav 4
Mar 1 30,000
207 2.9
6.5 23% OpNav 5
Apr 10 21,000
306 1.9
9.6 17% OpNav 6
Apr 14 14,000
453 1.3
14 49% OpNav 7


In addition to changes based on discoveries about the nature of Ceres, some changes are dictated by more mundane considerations (to the extent that there is anything mundane about flying a spacecraft in the vicinity of an alien world more than a thousand times farther from Earth than the moon). For example, to accommodate changes in the schedule for the use of the Deep Space Network, some of the imaging sessions shifted by a few hours, which can make small changes in the corresponding views of Ceres.

The only important difference between the table as presented in January and this month, however, is not to be found in the numbers. It is that OpNav 3, RC1 and RC2 are now in the past, each having been completed perfectly.

As always, if you prefer to save yourself the time and effort of the multi-billion-mile (multi-billion-kilometer) interplanetary journey to Ceres, you can simply go here to see the latest views from Dawn. (The Dawn project is eager to share pictures promptly with the public. The science team has the responsibility of analyzing and interpreting the images for scientific publication. The need for accuracy and scientific review of the data slows the interpretation and release of the pictures. But just as with all of the marvelous findings from Vesta, everything from Ceres will be available as soon as practicable.)

In November we delved into some of the details of Dawn’s graceful approach to Ceres, and last month we considered how the trajectory affected the scene presented to Dawn’s camera. Now that we have updated the table, we can enhance a figure from both months that showed the craft’s path as it banks into orbit and maneuvers to its first observational orbit. (As a reminder, the diagram illustrates only two of the three dimensions of the ship’s complicated route. Another diagram in November showed another perspective, and we will include a different view next month.)

to be added

Section of Dawn’s approach trajectory. We are looking down on the north pole of Ceres. (Readers who reside in the constellation Draco will readily recognize this perspective). The sun is off the figure far to the left. The spacecraft flies in from the left and then is captured (enters orbit) 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. When Dawn is on the right side of the figure, it sees only a crescent of Ceres, because the illumination is from the left. The trajectory is solid where Dawn is thrusting with its ion engine, which is most of the time. The labels show where it pauses to turn, point at Ceres, conduct the indicated observation, turn to point its main antenna to Earth, transmit its precious findings, turn back to the orientation needed for thrusting, and then restart the ion engine. Because RC1 and RC2 observations extend for a full Cerean day of more than nine hours, those periods are longer, both to collect data and to radio the results to Earth. Note that there are four periods on the right side of the figure between capture and OpNav 6 when Dawn pauses thrusting for telecommunications and radio navigation but does not take pictures, as explained here. Credit: NASA/JPL

We can zoom out to see where the earlier OpNavs were.

To be added

All of Dawn’s observations during the approach phase. Note how much shorter this caption is than the one above, despite the similarity of the figures. Credit: NASA/JPL

As the table and figures indicate, in OpNav 6, when Ceres and the sun are in the same general direction from Dawn’s vantage point, only a small portion of the illuminated terrain will be visible. The left side of Ceres will be in daylight, and most of the hemisphere facing the spacecraft will be in the darkness of night. To get an idea of what the shape of the crescent will be, terrestrial readers can use the moon on March 16. It will be up much of the day, setting in the middle of the afternoon, and it will be comparable to the crescent Dawn will observe on April 10. (Of course, the exact shape will depend on your observing location and what time you look, but this serves as a rough preview.) Fortunately, our spacecraft does not have to contend with bad weather, but you might, so we have generously scheduled a backup opportunity for you. The moon will be new on March 20, and the crescent on March 23 will be similar to what it was on March 16. It will rise in the mid morning and be up until well after the sun sets.

Photographing Ceres as it arcs into orbit atop a blue-green beam of xenon ions, setting the stage for more than a year of detailed investigations with its suite of sophisticated sensors, Dawn is sailing into the history books. No spacecraft has reached a dwarf planet before. No spacecraft has orbited two extraterrestrial destinations before. This amazing mission is powered by the insatiable curiosity and extraordinary ingenuity of creatures on a planet far, far away. And it carries all of them along with it on an ambitious journey that grows only more exciting as it continues. Humankind is about to witness scenes never before seen and perhaps never even imagined. Dawn is taking all of us on a daring adventure to a remote and unknown part of the cosmos. Prepare to be awed.

Dawn is 24,600 miles (39,600 kilometers) from Ceres, or 10 percent of the average distance between Earth and the moon. It is also 3.42 AU (318 million miles, or 512 million kilometers) from Earth, or 1,330 times as far as the moon and 3.46 times as far as the sun today. Radio signals, traveling at the universal limit of the speed of light, take 57 minutes to make the round trip.

Dr. Marc D. Rayman
7:00 a.m. PST February 25, 2015

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103 Responses to “Dawn Journal | February 25”

  1. Mike Fay says:

    Hi Marc, I loved your Deep Space 1 blogs, and these ones as well…

    I see that Dawn won’t be sending back pictures until April 10 due to being on the dark side of Ceres. Is this in part because it would have to interrupt what looks like an intensive deceleration burn (RC3) to point to Earth for high-gain pictures? Maybe doubly so because it would also use valuable photoelectric power to radio Earth, with a triple whammy that they’re just small crescents of Ceres anyway.

    I also read that you have to choose between photographing and pointing to Earth in the mission proper… could this be less a spacecraft design choice as a power choice? (The photos being low power, but radioing high power… so you take some pics, then burn up power radioing them?)

    I may very well have missed it, but if you can comment more on power balancing in future news releases, that would be great… ion drives are great in some ways but they must bring their own complications in others, which could help viewers root for the little guy using its power as best it can.

    I wonder if ion drives are limited to smaller craft for practical purposes… if you had a nuclear power source (and tons of power), it might add so much weight that the ion drive would be much less efficient in overall terms? (spacecraft maneuverability as a whole)

    Thanks and keep up the great work!

    • Marc Rayman says:

      Thank you, Mike. I appreciate your following DS1 and Dawn for so long!

      The reason for not taking pictures between March 1 and April 10 is that Dawn is over the night side of Ceres. I explained this in January and went into further detail in my two comments here.

      The choice between photography and communications is simply that when the camera is pointed at Ceres, the antenna cannot be pointed at Earth. In the same way, you can’t point the headlights of your car north and simultaneously have a side door open to the south. (At least, I can’t do that with my car.) You can do either one or the other. It is unrelated to power.

      Ion propulsion certainly requires high power. I have written about this extensively (see here, for example). But the benefit certainly outweighs the cost of the higher power. Dawn is not all that expensive by the standards of advanced planetary exploration, and yet the mission would be truly impossible with conventional propulsion. It would even be unaffordable within NASA’s Discovery Program if it attempted to reach only one of Dawn’s two destinations using conventional propulsion.

      NASA recognizes that more power would be beneficial for larger missions using ion propulsion. However, as I described last year, conventional nuclear power sources are not the answer, as they provide too little power. For some missions, power levels comparable to Dawn’s would be quite satisfactory. For others, either larger solar arrays or advanced nuclear power systems, using technology which does not yet exist, would be required.

      Thank you again for your interest!


      • Isaac says:

        Is there a suspicion that the bright light can come from an active light source at all? If so it does seem to make sense to take some photos from the dark side too. Isn’t it?

  2. Dragos says:

    Has Dawn found any evidence of moons around Ceres yet? Or is it still looking?

    Thank you for this amazing Journal!

  3. John Reed says:

    I know the IAU want to use gods of agriculture to name craters, but it’s pretty clear to me that the crater with the bright reflections needs to be named “Motel6″…looks like they left the lights on for us!

  4. Matt says:

    Hello Dr. Rayman,

    in my view most recent images of Ceres confirm model prediction about crater appearances for a body with significant ice shell/mantel, which is relaxed and flat where sunshine flux is stronger and deeper and less relaxed, where sunshine flux and therefore temperature is very low.

    What do you think?


    • Marc Rayman says:

      Hi Matt,

      Your view is interesting.

      I grew up as a physicist. I prefer not to reach scientific conclusions without hard data. I think that to confirm a meaningful model, one should compare a quantitative prediction with a quantitative result. So I will reserve judgment on this aspect of the nature of Ceres until we have acquired more data on the crater shapes, sizes, distribution, etc. and the science team performs analyses to determine what that reveals about the strength and other properties of the material. To me, the beauty of science lies in part in how powerful it is, and so I like that power to be used.

      Others may wish to offer their own opinions and speculations…


  5. Ben says:

    Dear Marc:

    With Dawn spiraling into it’s observational orbit, and vast amounts of data and images about to begin arriving, I wonder if you might be planning on giving us more frequent updates during the observational phase? I’d also love to hear about the things that your team is speculating about what we are seeing as you go along. …You could put disclaimers about your speculations…

    Also – if the twin bright spots were actually plumes of vapor, wouldn’t you expect them to look much more diffuse than they do in these pictures, given that resolutions are down to a few miles and the atmospheric pressure on Ceres must be about zilch?


    • Marc Rayman says:

      Hi Ben,

      Thank you for your comment. I would very much like to provide more frequent updates, and I’m glad to know you are interested.

      As I’ve mentioned, I write these Dawn Journals in what would otherwise be my free time. It turns out that that time is not as easy to come by as I’d like, so I also end up writing in a big rush. You probably won’t be surprised that the mission itself requires my attention sometimes too. I had planned to write this February Dawn Journal sooner than I did, and I was disappointed with how long it took me to get to it. But I’m not very good at keeping up with all the questions posed here on the blogs. I write slowly and when I do write, I often do it in bits and pieces, which is inefficient. Even a brief question can be time consuming to answer. Any one may be easy. All of them together, along with the emailed questions, take the time I would otherwise devote to providing the updates. As a result, I regret (honestly!) that I cannot say whether I will be able to give more frequent updates. I will try :-) I also will try to answer as many questions here as I can (including whether I will provide more frequent updates). I am very happy to have so many enthusiastic people along for this exciting adventure.

      And so, in that spirit, as I have commented several times, I will not speculate here any further about the bright spots. It’s not for lack of interest or enjoyment, but simply a matter of time.

      Once again, I’m very grateful for your interest as well as that of all you other loyal readers, whether you post questions and comments here or not.


  6. Hello everyone, I am excited to new photos and for your great work; I’m very happy, and my question was read in the ” Dwarft planet arrival, nasa jpl, March 2″ (latest Question) :-D
    This is my final collage, very accurate, I have represent in accurate scale Ceres, Vesta, the most important asteroids visited by a space probe, 3 icy moons (Mimas, Miranda, Enceladus), Mars moons (Phobos and Deimos) and the strange asteroid Chariklo (as I have imagined).
    I hope all like it.
    Daniele, Italy

  7. Romana Starfield says:

    Ohh, I just saw the latest images. I like the new animation
    It is amazing! I’m so happy to see that. It helps bring the little planet to life for me. It also demonstrates that the two bright spots indeed only shine as the sun reflects off of them. I note from the table in this month’s blog entry that the next couple of imaging captures, Optnav 5 and 6 will be of greater resolution, but only cover a small portion of the surface of Ceres. So we will have to eagerly await further developments.
    I also eagerly await some official names for the features, and the chice of where the prime meridian for Ceres will be.
    Once again, no need for a reply, just thinking in writing.

  8. Sean Deany says:

    Marc I love the intro video [here] and especially the box of Ceres-os. Perhaps NASA can finance a human mission to Ceres from the sales of that breakfast cereal! Put a trade mark on it fast. The taste may be something a little like frozen unsweetened blueberries perhaps?

    On Friday 6th in celebration to mark Dawn’s arrival at Ceres orbit I will be travelling to Ceres myself. I’m not joking as it only requires a 50 minutes train journey from Melbourne’s Southern Cross Station and a 18 km return walk from Geelong Railway Stn. Yes there are multitudes of Ceres on this world! It will be a small sample return mission in preparations to a 3 months walking tour in Europe I’m commencing later this month – where indeed I will visit another dwarf village called Ceres – in Piedmont Italy!

    Importantly those pictures of the “real” Ceres just keep getting better. Evidently there is a beer called Ceres and if the JPL bar have it on tap please have one for me as its not available where I live.

    • Rob Krieger says:

      being a danish follower of this blog, I can confirm that the Ceres beer exists and is very tasty too. The brewery was founded in 1856 in the eastern part of Jutland, Denmark, Earth – named after the Goddess of grain crops and fertility.

      • Sean Deany says:

        Thanks Rob will search for it and see if its available here in Australia. Perhaps the Ceres brewery in Denmark could send a sample to Ceres and back, where from the bottle fermentation make a commercial batch in efforts to finance the first human mission to Ceres!

    • Hi Sean.
      Yoou don’t even need to go as far as Geelong. You can catch the tram up to Brunswick and vist the Ceres learning centre and eco farm;
      I used to walk past that all the time. THey probably have more life in those 4 acres than all of Ceres the minor planet. Certinly more chickens.

      That’s my second favorite Ceres.

      • Sean Deany says:

        Funny you say that Romana as I live along the 96 tram route. My landlord who hates technology and me talking all the time about the dwarf planet 1 Ceres is today attending a friend’s wake at the CERES Environment Park. It seems nobody when in my company can escape Ceres! I thought that travelling to the village of Ceres might give him some respite as well will be more of a challenge in my preparations for a 1650 km walk I’m soon to commence in Europe.

  9. Mark says:


    It seems like you need to turn off the ion engine and rotate the spacecraft to point and use the camera. What is the reason the camera is not mounted on a pan-tilt or gimbal mount? It would then have 180×180 degree or better view. You could even photograph the spacecraft itself.


    • Marc Rayman says:

      Hi Mark,

      As a (possibly interesting) detail, we need to rotate to point the camera. We do not necessarily have to turn off the ion engine. Indeed, I explained in November that we turned on the ion engine for those pictures of Ceres. We invented this technique on Deep Space 1, where I called it impulse power.

      There are many facets to the answer to your question, but in the interest of time, I will address just one of them: the cost. Making a movable structure that would provide a stable platform for the precious photography and other measurements would have been unaffordable. Dawn is relatively low cost for an interplanetary mission, despite the fact that it accomplished feats that would have been impossible for other spacecraft. We have a primary camera plus a backup camera plus a unit that combines a visible mapping spectrometer and an infrared imaging spectrometer. (We also have gamma-ray and neutron spectrometers, but we don’t use them during the approach phase.) We would need a device that could position all of those massive devices, with their attendant cables, so that regardless of the spacecraft orientation, they would have a view of Ceres unobstructed by the spacecraft or its giant solar arrays. It also would have to ensure the sensors are protected from the sun. The cost required to make such a system work reliably on this very long mission with a tremendous range of temperatures is truly prohibitive.

      Spacecraft designers generally prefer to avoid moving parts whenever possible.

      I hope this answers your question.


  10. Bertrand Ouellet says:

    Dawn is a remarkable achievement, and I should add that your blog is one also. Many thanks for your dedication.
    With all those features clearly visible, it is already difficult to keep track and refer to this crater, ring, basin, smooth area, mound, “spot”, etc. Any idea when (provisional) names or designations will be available ?

    • Marc Rayman says:

      I appreciate your nice comment, Bertrand!

      For others, the naming convention for features on Ceres was explained here.

      Yes, I agree with you about how cumbersome it is to refer to specific features. I expect the team will formulate proposals in May when we have the more detailed views from RC3 orbit, and the International Astronomical Union probably will approve them a few weeks later.


  11. Luis says:

    In relation with Ceres’s Pancake feature, interesting to look elsewhere for some similarities of “shallowness”, in this case from Saturn’s Tethys moon:


  12. Luis says:

    Hi Marc and bloggers,

    In reference with the recent imagery uploaded to the site, I notice that just above the “south pole” of Ceres depicted in the animation:, we can also notice another very shallow basin. Curiously, to the NW of its northern rim, we can identify those linear fracture lines (?) I had mentioned before. See for example the frame at 0:13 seconds. Might these linear structural morphological features be related or not with the southern pole basin? We shall see has better imagery will stream back, I presume would be your answer for now. Overall, the shallowness of this southerly basin looks to have some morpho similarities with the one closer to the equator, and highlighted in the text description of image: Pancake_Feature_Ceres.asp.


  13. Typo91 says:

    These bright spots are a reflection of sunlight right? I mean cant you analyze spots and pick apart the sun’s spectrum from the pixels captured on the CMOS in the light to confirm its a reflection of our own star’s light?

    Its not like its a light source on Ceres right? That is already ruled out I take it for sure right?

    I think I read somewhere its a 40% reflection of light, so I am assuming a large sheet of ice that probably formed on the surface from some event that melted some water, and is now smooth and has a thin layer of dust on it.

  14. Joe C says:

    It has been said before, but thanks for taking the time to write this blog.
    I am embarassed to say I did not know much about this mission before the pictures of Ceres were released with the dual bright spots, it’s interesting that a single picture can capture the imagination /attention so quickly.

    Good luck to the team for the rest of the week; looking foward to good news this Thursday night.

    • Marc Rayman says:

      Thank you for your kind comment, Joe! Rather than be embarrassed, you should be happy you know about it now. We’ve had more than seven years of great adventures on this deep-space trek, so you’ll have fun getting caught up :-) And I’m glad to know you’ll be along for the excitement ahead.

      Orbit entry is now planned for Friday morning.


  15. Jaheira says:

    Since Dawn is now moving away from Ceres, on what date will it reach its furthest point before approaching once again? And how far away from Ceres will it be at this date?


    • Marc Rayman says:

      Hi Jaheira,

      On March 18, Dawn will reach its maximum orbital altitude of about 47,000 miles (75,000 kilometers). This is still very close to the plan I described in detail in November.


  16. Steven Taylor says:

    Whilst I appreciate films give a completely wrong impression of the amount of material in the Asteroid belt, as Dawn will be there for several years, what is the risk to Dawn from a meteor strike. Although unlikely I guess, has a dust ring around Ceres of a very low optical depth been completely ruled out?

    • Marc Rayman says:

      Hi Steven,

      We analyzed the risk carefully as part of designing the spacecraft, so, as I explained here, this is not considered to pose a significant threat to Dawn.

      For others, “low optical depth” amounts to meaning sparse here. While a dust ring has not been completely ruled out, it is considered to be much too unlikely to worry about.

      Of course, we scrutinize all of the images for any important features, and some of our longer exposures for the moon searches would help for dust. As you know, photos taken on the side of Ceres opposite from the sun (as, for example, OpNav 6) would be most revealing. For others, I apologize for simply not having time now to explain this, but in brief it is because small particles show up best at that angle. It’s why your dirty windshield (or, at least, mine) lights up most strongly when the sun is ahead of you: all those tiny particles redirect the light nearly in the same direction it was going when it hit them. So the best way to see them is to align your viewpoint to be close to the source of the illumination.


      • Steven Taylor says:

        Many thanks for response, and especially the link to your 2009 article. Very informative article. I am fairly new to this site and must look at earlier articles. So much information. I am finding the Dawn images to date so interesting and I guess that the crater distribution, to a complete amateur, looks to vary all over the surface, so some re-surfacing has surely taken place. What with New Horizons at Pluto/Charon this year, it is reminding me of the excitement I had with the first Mariner pictures of Mars in 1965, and especially the Voyagers at Jupiter in 1979, and the subsequent Miranda/Triton pictures. Although no internet in those days. But JPL were good to me, and used to send complementary colour slides when I used to make a request for images.

  17. Matt Gibbons says:


    Excuse me please for getting ahead of myself with this question, but since you are at the apex of project management I’d like to ask you what would be your pick for the follow-on mission that will take ion propulsion to the next level? I realize this is an “over the horizon” question, but I’m virtually (and a bit presumptuously) certain that you have other missions on your wish list, at least one of which will advance ion propulsion to the next level of capability.

    I know your in the zone now with a laser focus on Dawn and 1 Ceres, but back in the recesses of your mind, where wishes become reality, what is your personal dream mission? Certainly the asteroid belt holds vast targets for future missions.

    • Marc Rayman says:

      Hi Matt,

      There are many exciting missions I’d love to undertake. It’s already been like a dream come true to work on the first interplanetary mission to use ion propulsion, Deep Space 1, and then to apply it to the fabulous Dawn mission to two of the last uncharted world in the inner solar system. I have emphasized ion propulsion to the public (I even chose the name because I knew science fiction fans would resonate with it more than they would with other names that were considered for DS1’s advanced propulsion system), and I worked hard to learn how to take advantage of its extraordinary capabilities and how to accommodate its many differences from conventional propulsion. But it is not my focus. To me, it is one tool in the toolbox of mission designers. It isn’t the right answer for every mission. I’m interested in the ultimate outcome of missions but not necessarily which tools we use to accomplish them. But I do love this tool, and I should point out that ion propulsion can enable wonderful missions to destinations other than the asteroid belt. It just so happens that that is where Dawn is using it. I think NASA’s plan for taking ion propulsion to that next level with the Asteroid Redirect Mission is very exciting, and that may lead to it being a vital part of humans traveling to Mars.

      You’ll note, however, that I didn’t answer your question. I danced around it. Well, I love dancing, but this wasn’t very graceful. There are too many good missions, and to explain my choices or my preferences will take time I cannot afford right now.

      For now, as you recognized, I will focus on Dawn at Ceres. I hope doing so will contribute to fulfilling wishes that you and I and many other readers have for discovering new realities about the cosmos.


      • Matt Gibbons says:

        I’m betting you wouldn’t be averse to being project manager of a Uranus orbiter! Basically, the reason I mention that one is, I want to see the other side of Miranda! Also, the Midsummer Night’s Dream Moons (Ariel, Umbriel, Oberon, Titania etc) are fairly screaming for photo coverage!

        A Uranus orbiter is my choice for the next mission to be funded regardless of ion propulsion usage.

        We can dream.

  18. Guillaume Vollant-Boulé says:

    This is awesome, cannot wait for OpNav 4!!!

    Thank you Dr. Rayman,

    Guillaume Vollant-Boulé

  19. Jim says:

    You provide the details I want to read. This has been an exciting mission of discovery. As a former high school physics teacher and amateur astronomer, I am really enjoying the show.

    Keep up the good work, Dawn…Live Long and Prosper!


  20. Phil Karn says:

    How important is solar radiation pressure in the maneuver planning for Dawn? Does it help or hurt?

    At 1AU I estimate the radiation force on the arrays normal to the sun at 164 micro newtons, and of course it drops at greater distances. Small compared even to the ion thrust but not zero. And it’s continuous.

    • Marc Rayman says:

      Hi Phil,

      For others, solar radiation pressure is the slight pressure exerted on the spacecraft by the light of the sun. I have mentioned it a few times, including here. It is often mistakenly thought of as being a result of the solar wind, but it is from the light itself. (In this terminology, “radiation” refers to electromagnetic radiation, which is light.) This force is entirely negligible under most circumstances here on Earth, but its effects on spacecraft can be important, as Phil recognizes. As he also observes, it depends on the distance from the sun. Sunlight is weaker where Dawn is now that it is at Earth.

      Your calculation is quite close. It’s not quite that high, but it’s certainly in that range. So, roughly speaking, it is about one thousand times smaller than the thrust from the ion engine. You are quite right that it’s continuous, whereas we do not operate the ion engine all the time. (There are various reasons we do not always want to thrust. So far, we have thrust for 69 percent of the time in space. No other spacecraft has spent as much time in powered flight as Dawn. Most spacecraft coast for the overwhelming majority of the time, just as planets do.)

      As all interplanetary missions, we must account for this effect on Dawn. It isn’t so much a question of whether it helps or hurts. Rather, it’s one of the forces acting on the spacecraft we include in our navigation analyses. With Dawn’s complicated interplanetary trajectory, aspects of which I have described in too many Dawn Journals for me to recommend any particular one right now, we need to push the spacecraft in different directions, so the contribution of sunlight to the desired outcome varies. In orbit around Vesta and Ceres, the trajectories are even more complicated and so it is even less meaningful to describe it as simply helping or hurting. Every time we update the flight plan, the solar radiation pressure is incorporated into the calculations. If it were absent, we would point the ion engine in a slightly different direction and the schedule for thrusting would be slightly different. When we analyzed Dawn’s orbital fate at Ceres, projecting what would happen over many decades, once again solar radiation pressure was one of the forces taken into account.

      I hope this answers your question.


      • Phil Karn says:

        Hi Marc, thanks for your quick reply! By “help or hurt” I meant to ask if the presence of solar radiation pressure has reduced or increased the total delta-V you had to produce with the ion engine.

        Also, has it been possible to orient the solar arrays to put the radiation force in a useful direction? When the ion engine is not operating you must certainly have a large power surplus that would let you offset the arrays from the sun if desired.

        Hmm. Now that I think about it, the arrays are highly absorptive, so unlike a solar sail designed for the purpose there’s no extra momentum from reflected photons. Maybe the force would be directly away from the sun regardless of array angle. This assumes the arrays are thin enough to be at the same temperature on both sides so their thermal radiation nulls out. Remember the Pioneer “anomaly”? Asymmetric thermal radiation can be important.

        • Marc Rayman says:

          Hi Phil,

          For others, to understand what Phil means by delta-v, see my comment last month. For our purposes here, it’s equivalent to the total amount of ion thrusting we do.

          You clearly have a good understanding of the technical issues, but I’ve tried not to get into topics in these blog comments that leave many readers out. Perhaps that doesn’t seem fair, but that’s my preference. And much to my regret, my own time is so very limited that I can’t always explain the issues to other readers. So I’ll be brief here.

          For most of the mission, the presence of the solar radiation pressure means we have to thrust very slightly less than we otherwise would (and, again, in a different direction and on a different schedule). In some phases of the mission, however, we actually propelled Dawn toward the sun (though that is counterintuitive, I wrote about it once here) and so we had to thrust more to counteract the solar radiation pressure, like fighting a headwind. Averaged over the mission, it has helped in the interplanetary travels. In orbit around Vesta and Ceres, it’s too close to call, and we have never run a detailed analysis without solar radiation pressure, so I don’t have a quantification.

          Some spacecraft orient their solar arrays (or vanes attached to the solar arrays) to take advantage of the pressure. Some included this in their original designs and others, like Mariner 10, developed it in flight. We have not done that on Dawn for very technical reasons. Some of the more than 50 candidate methods of conserving hydrazine included that, but we did not adopt them. (As I’m sure many readers know, solar sails depend on this idea of deflecting the sunlight in a useful direction. It’s no different from the sail on a boat, but I will not get into that. I only barely have time to write about Dawn.)

          I hope this high-level answer is helpful. Thank you for your interest!


      • Johan Prins says:

        WOW! *that* is an answer I rarely see on any space mission forum (the last one I posted on was the Rosetta mission forum, where *loads* of questions were asked, and *no* answers, other than from other visitors, were posted ever.)

        Thank you very much for making that difference.

        ..Maybe it helps when the person asking is our competent, long-time friend, Mr.Phil Karnes back from the Amsat heydays, and who lately was involved in the ICE-3 “reboot” project that unfortunately became a fly-by.

        As probably everyone else, I will have my nose pressed flat against my screen as it were, as pictures from outer space will come right to my desk, like it first happened with Sojourner’s pictures when I just had Internet.

        How near to Ceres do you plan to go? (of course, you will need to measure the regularity of it’s gravitational field before any final decision on that). Maybe you plan a “scraping descent” as end-of-life option? Too rearly to ask, I guess.

        • Marc Rayman says:

          Thank you, Johan. It means a lot to know my comments are appreciated! And I am very grateful for your interest in the mission.

          We have planned to spiral down to an orbital altitude of 230 miles (375 kilometers), which we will reach near the end of this year. I presented the plan for the end of the mission in detail here, where I also explained that we will never send Dawn to the surface of this fascinating alien world. Ceres is too important!

          Thank you again.


  21. Matt Gibbons says:


    Not to go too off on the great White Spot debate, but the images we are seeing are obviously processed to bring out detail on 1 Ceres, which causes the images of the white spot to over-saturate. Is there digital data within the images to go the opposite way with the processing and allow 1 Ceres surface to under-saturate, thus losing detail of the dark surface, but bringing up the detail that might be available within the few pixels that show the highly contrasting white spot(s)? Obviously, there are very few pixels to play with in this regard, but perhaps this will be the technique that will finally (when Dawn is much closer) once and for all, reveal just what the heck those “bright” features are!



    • Marc Rayman says:


      The team is still analyzing the pictures, but they don’t contain enough data yet. To elucidate the nature of these bright spots, in addition to good exposures, we need higher resolution. We had always planned that we would use the approach images to finalize the exposure times we will use when Dawn starts its first intensive observations in RC3 orbit at the end of April, and we are in working on that now. The resolution in RC3 will be 3.4 times better than RC2. Whether that will be sufficient, we will discover in two months. If it’s not, we’ll get three times better than RC3 in survey orbit, then three times better than survey orbit in HAMO, and then four times better than HAMO in LAMO. Eventually, we will know the secret.


      • I like this, a steady wins the race approach. All will be revealed in time.

      • Matt Gibbons says:

        An enigma within a mystery! This is what it’s all about, like when the public was allowed to see images, line by line, coming down from Voyager 1 as it looked down the maw of Loki Patera. No one knew at that moment what they were looking at…which had all the ear marks of an ink lake! But Voyager was literally looking down the barrel of a volcano in full eruption. The voice of JPL, Al Hibbing was the host of the daily broadcast on PBS back in 1979 and I seem to recall that he pretty much was slack jawed by the image building line by line.

        Bring it on Great White Spots…Dawn’s team of explorers have got you and now they just need to reel you in! I suspect that whatever it is, it’s going to be surprising!


  22. Kamal Lodaya says:

    Marc: The spot resolved into two is seen almost from its zenith. Could some of the other spots, seen from their zenith, also get resolved into multiples? Or are we sure that at the current distance from Ceres there is only one such pair we can see?

    • Marc Rayman says:


      People love to speculate, but until we get pictures with higher resolution and from different perspectives, we cannot know what they will show. That’s the lure of exploration! I look forward to Dawn revealing the answers to your questions!


  23. Luis says:

    Ceres features similarities with Vesta.

    Looking at the recent imagery from Ceres, and going back to some of the data available on Vesta’s portfolio, it is interesting to look at some of the morphological characteristics of particular features, that might help in hypothesizing at this stage on similar backgrounds for their appearance, and surface patterns.

    For example, in the recent image “Two Views of Ceres on Approach – CeresBig_LR_lg.jpg”, the apparent more recent impact crater in the center of the right-side depiction of Ceres, seems to hint for a relatively “fresh” material covering the inner crater and immediate vicinity. This might be perhaps similar with the surface characteristics observed in this “younger” impact crater on Vesta:

    Also, and in the same image of Ceres, upwards from the prior location, one can see a brighter area on the 4 o’clock side rim of another potential impact crater. Perhaps these lighter recorded surface conditions could be similar to the ones observed in Vesta, and captured here:

    These are all preliminary perceptions, that Dawn instrumentation and data will certainly clarify, answer and reveal a lot more in the coming weeks.

    Thank you again for allowing this incredible collective discovery journey!


  24. johnnymorales says:

    I was just wondering why there is no effort graphically enhance the photos (beyond leveling the contrast)to bring out details that are easily brought out? Considering the details I can bring out using what i have, I imagine with the advanced tech at your disposal, you could make the image look crystal clear :)

    • Marc Rayman says:

      Johnny, the Dawn team uses the images for specific quantitative navigational and scientific analysis. There are many ways to make them look more visually appealing or to emphasize different aspects of the images (or the data the images contains), and we know that there are many capable people — like you! — who do a great job with that. We encourage people to enhance the pictures any way they like to bring out details of their choosing while the team is focusing its efforts elsewhere.


  25. Daniele Bianchino says:

    We more and more ‘happy.! :.)
    WHY The RC2 image of the two hemispheres have major resolution of than
    RC2 image of the hemisphere with the “two bright spots”?
    Many ThanKS

    • Marc Rayman says:

      Hi Daniele,

      The actual resolution of the original images are all the same. Different processing was applied to some images before they were released, so that makes them appear somewhat different. The presence of the bright spots, which are still too small to be resolved by the camera, led to different choices in how to present that picture. This was a by-product of the effort by a busy team to release multiple images.


  26. John Turner says:

    Tell me if I’m crazy, but the northern hemisphere’s bright spots show signs of being Gas Fountains. A gas fountain is like a geyser but operating in a near-vacuum, where the gas leaving the geyser rises in a streaming jet, opens into a domeshaped plume and then drops to the surface of its own weight.

    These Gas Fountains are difficult to see directly, but they do give their clues.

    At Jupiter’s spectacular moon Io there are vast plumes of volcanically-erupted sulfur dioxide gas that can span hundreds of miles across the surface, yet are so transparent that they might never have been noticed from looking face-on at Io itself. They were first discovered by a JPL spacecraft navigation team not the geology team, who whilst picking through their navigation frames happened to note a faint bright region standing clear of Io’s visible limb. That bright region is sunlight scattering off otherwise invisible gas molecules, and it’s brightest when seen from angles within ninety degrees of pointing at the Sun. It happens to be a lovely robin’s-egg blue in color, and is due to the same Rayleigh Scattering Effect that makes Earth’s daytime sky look blue.

    Knowing where to look, the geology team checked face-on photos of Io and matched up the Nav Team’s “limb plume” with a soft shadow cast on daytime Io by the same plume. Earth’s entire surface is covered by a similar shadow, the difference between bright raw sunlight and the dimmer, yellower sunlight attenuated by Rayleigh scattering.

    Similarly we may be seeing something big and invisible on Ceres today, by its Rayleigh-scatter shadow. Note the dark “eyebrow” feature that extends north to northeast of the prominent bright feature in the OpNav 3 movie loop; that could be a shadow cast by a descending gas plume. And note the fingerlike dark features visible in the RC2 frame extending northwards from each of those doubled bright features; those could be the shadows of the rising gas jets feeding the plume. Similar shadows are visible at Io and at Triton, and they matched up to fountain and jet activity there.

    The best proof of plume activity would be found in images taken when Ceres is mostly in shadow when seen from Dawn, when the solar angle is so close to the line of sight it’s just off frame.

    Are the Dawn science team thinking about taking such photos?

    • Marc Rayman says:

      Hi John,

      With regard to your opening request, I’m happy to tell you about the mission. I’ll leave assessments of psychopathology to people who have both expertise and time :-)

      You might find the comments by several of us last month about the possibilities of geysers to be interesting.

      You are quite right about the best viewing geometry for searching for water vapor above Ceres. I explained here that last year we did indeed add measurements to our first science orbit much like what you suggest. In addition to images, we will acquire spectra. (As an aside, I think it is noteworthy that, even with the loss of two reaction wheels, we are now planning to conduct even more observations of Ceres than we had planned when Dawn embarked on its interplanetary expedition with four healthy wheels.)


  27. Richard Roy says:

    As a retired geologist and mining engineer my best guess is that it is glass, not artificially made glass but the kind of glass that was created by the first A-bomb test at Trinity called Trinitite. When lightning strikes sand and creates Fulgarites it is the same process. The fact that the brightest light is at the bottom of a crater suggests a molten material settled there and if the meteor that impacted there was full of silica or it hit a silica rich section of Ceres or both that could explain the presence of so much Trinitite, or perhaps that meteor was coming in extremely fast and created a more intense impact than normal. I am sure that different varieties, especially natural glass can produce quite different reflection ratios.

  28. James Lovelady says:

    Dr. Rayman, thanks for not waiting until the first of the month for the update–I have been checking DAILY to see the latest pictures and the latest speculation on Ceres’s features as they come into view. It has been a thrilling ride to hear some of the daily goings on from you and your crew over the last several years. We ALL have big dreams of discovery and exploration, so I just wish to express my sincere thanks for sharing the journey. I think I can say that I am equally entranced by the slow playing out of NASA’s robotic missions as I was when I was glued to the grainy B&W broadcasts from the Apollo missions “back in the day.” What a GRAND success you guys have had introducing the next generation to the challenges and thrills and new science that exists outside our atmosphere. Good luck in the next year, I fully expect to be awed by Dawn, and by Cassini, and by New Horizons, Curiosity and Opportunity, SOHO, JWST… Keep your geek on, sir. -jim l.

  29. Mewo says:

    Thanks for another interesting and informative post.

    The new images are brilliant. It’s striking that so many of the craters follow Ceres’s surface curvature, so that they are convex. It makes Ceres look kind of smooth and cratered at the same time.

    And those white dots are becoming more and more intriguing. They are smaller and brighter than I would have thought possible. I’m sure there’s UFO enthusiasts all over the world in a frenzy of excitement over the white dots! I can’t wait to know what they really are.

  30. Matt says:

    Hello together,

    Dr. Schaefer from German Max Planck Institute said yesterday that picture resolution of about four kilometers is too small to resolve dimensions of both bright spots. That means that both spots can be even much smaller as 4 kilometer. I made yesterday [see here] a joke about it: What about if see an alien light house? :-) No, being honest, I think it is pure ice, which contrasts extremly to the surounding surface, which is dark as coal.


  31. Steven says:

    Marc, a huge thanks for the effort you’re putting into these posts. They are both very educational and fun to read.

    Is there anything that discusses what direction the spacecraft is thrusting in during these maneuvers? It would make understanding the orbital entry much easier for me.

    • Marc Rayman says:

      I appreciate your kind remarks, Steven. I’m glad you enjoy these. As I’ve written, I always do them in a rush, and it’s hard to keep up with the comments, so it’s gratifying to know it is worthwhile!

      I described a little about the direction of ion thrusting in November, and you might find that to be helpful. In addition, I hope to include a very different way of looking at the nature of this unique trajectory in my Dawn Journal next month. I think it will give a clearer idea of how Dawn swoops into orbit.


  32. Romana Starfield says:

    Whoa indeed! The latest pictures are stunning. Lots of surface detail. I love the large shallow crater shown on the left of the latest image pair . It looks like a 5 ad shown on a dice. Meanwhile one of the lighter spots on the right side of the paired images looks like it might have a vague ray structure.

    I love how Marc suggested on his February 18th comment reply to Paul Kuenstler that “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.” Indeed that’s what it appears to be at this stage, well a pair of smaller brighter features. Some mysteries are revealed, some grow deeper. Ceres is revealing some of itself, but leaving us with plenty more to discover.

    I now wait with anticipation until Dawn takes up orbit around this small but mighty planet and we start to get even more images. Thanks again to the team, and Marc in particular for the updates. No reply needed for this, I’m just voicing my thoughts.

  33. Matt Gibbons says:

    I must say, in photo “Ceres With Two Bright Spots” the six o’clock position on the globe appears to be chaotic. There are notable parallel troughs running through the entire area, some nearly vertical to the POV of Dawn and others that look to be radial.

    As to the two “searchlights” side by side….?????

  34. Congratulations on these first-time ever photo’s; they are amazing and they will keep us in very good company until OPNAV6 (10APR’15). I was wondering if you could possibly “map” the newly discovered “binary bright spot” to either of the paired PICs (of Ceres) from RC1 and RC2.

    Thanks again for all you do for this mission and Godspeed to your crew.

    • Marc Rayman says:

      Thank you for your nice message, Stephen.

      I’ve tried to avoid getting too much into detailed coordinates because it may be more obscure than many readers are interested in, and it can be time consuming to explain all of the issues. One of my colleagues helped me do this quick mapping. The left image in the RC2 pair is centered around 116 degrees and the right one is about 17 degrees. The view with the two bright spots is about 244 degrees. Therefore, the spots are about 128 degrees east of the view on the left and 133 degrees west (227 degrees east) of the one on the right. (Note in the comment immediately below that I had originally typed 277 instead of 227.)

      I hope this brief description is helpful.


      • Stephen Sullivan says:

        Thank you, Marc; you’re an inspiration to all of us (particularly to my twins down at UVA with their dorm on Observatory Hill – Home of the 1884 Leander McCormick Refractor).

        Given your collegue’s well-intended mixed use of East/West Longitudes and radian(e.g. the 277 degree measurement seems to me to be 227), can I safely say that, as an observer starting at 0 degree meridian, I would first see the the binary brights (244 degrees), followed then first by the left photo of the pair (116 degrees) and then finally the right photo of the pair (17 degrees). It would certainly make sense this way, given the way the photos have been (taken and then) laid out.

        Thanks again for your consideration and time.

        • Marc Rayman says:

          Hi Stephen,

          The errors you cite are mine, not my colleague’s. He used only east longitude. I added west in hopes it might be clearer for readers who aren’t accustomed to longitudes in excess of 180 degrees, although it may have created confusion. And I introduced the typo of 277 in my rushed response. He correctly wrote 227. (For clarity: I have now edited my response above so readers don’t have to follow a thread if they care about the correct values. But Stephen is correct: I had typed 277 instead of 227.)

          Your description of the sequence of observing is correct.

          Thank you again for your interest!


  35. AmbiValent says:

    What’s known about the surface of Ceres? Is it made up out of the stuff that rained on Ceres over the billions of years of its existance, covering the ice that was the topmost layer when Ceres was formed and the heavy elements sunk down to the center? Or is Ceres more like Callisto where it was too cold for that?

    • Marc Rayman says:

      Hi Frank,

      Ceres’ surface certainly includes accumulations from the tiny objects that rained down on it. There may be even more material from large bodies that distributed their contents over the surface when they impacted.

      If you’re asking whether Ceres has a differentiated core, yes, I mentioned in December that this is likely the case. The thermal models I referred to last month do indicate that at some time in the past, ice melted and heavier rocky material sank. Our measurements of the gravity (as explained in August) should reveal more about the interior structure.


  36. Sean Deany says:

    Marc the clarity of the RC2 images are really stunning and I thought RC1 images were out of this world!

    All the best of images so far I have printed, scrutinized and as you know have posted some on my blog site. However its the area known as Region A illustrated for the Imagine Ceres page, which hasn’t appeared to my understanding since OpNav 3. It was where water vapor was first detected by the Herschel observatory and its bright spot – my favorite spot which comes into the question. Nonetheless is the single image above with the twin bright spots actually Region A as seen in the OpNav 3 motion film?

    Interesting is that still the 2004 “colour” Hubble images are useful reference points and surprisingly they indeed reveal what are now overwhelmingly prominent features. Though DAWN is making great progress I fear we are still in the Dick and Jane stage when it comes to finding Spot (bright spots of Ceres that is).

    • Marc Rayman says:

      Hi Sean,

      I agree the images are stunning. And just as RC2 is better than RC1, if all goes well, in a few months we’ll consider these to be fuzzy.

      For others, “Region A” is a provisional name for a band of longitude (that is, a region extending from pole to pole) in which scientists thought there might be a source of the water vapor I described here. Yes, the single image with the twin bright spots does correspond to Region A.


  37. Matt Gibbons says:

    Just for a point of comparison, 1 Ceres has significantly greater surface area than Greenland. Greenland has approximately 2.16 million square kilometers while 1 Ceres has approximately 2.85 million kilometers. A lot of real estate to investigate!

    Regarding the white spots, the one in the center of the right image appears to have radial ejecta pattern originating from that crater. It looks like a splash crater that revealed lighter materials when it laid out the craters extensive ejecta blanket.

    • Marc Rayman says:

      You’re quite right that Ceres is huge, Matt, and there will be a great deal to study there. I offered some other comparisons for its size here. Now we can start to compare not only Ceres’ size with Greenland or elsewhere but also its geology!


  38. Meastn says:

    Some citizen science time! Blessed by simple digital paint tools and ignorance of math. I tried to unravel our beloved bright spots and their size comparison as well as put a comparison map as if they were on New York city area.

    Check out the size comparison of the MYSTERIOUS BRIGHT SPOTS of Ceres from @NASA_Dawn :info graph by me— Melih R. ÇALIKOGLU (@Melih_CALIKOGLU) February 26, 2015

    • Robert Griner says:

      I like what you did, Melih! The terrestrial perspective makes the mystery resonate more.

      • Romana Starfield says:

        That was rather cool. From the table in this and the previous blog the Feb 19th images are at a resoloution of about 4.3 km per pixel. That may make for an easier calculation. The spots may be even biger than predicted. But they may also be smaller, and just very bright, like when you get a sun flare off of a shiny object in a photo.

        Either way this is all still very cool and that image you made helps bring this all down to Earth for me.

        • Meastn says:

          Thx, Romana and Robert

          Measuring pixels is also awesome and it also happens to correlate my guess as the width of the bigger spot being 8.5 km
          As you said if the spots are smaller it means a much brighter matter lying right there making it much more exciting. Can’t wait for 6 more weeks.

  39. Keep up the great descriptions! I’m highlighting Dawn this semester to my general education
    astronomy class at U. Louisville as “exploration in real time”.

  40. Gary Crawford, Ph.D says:

    Looking at the right hand side of latest photo (feb 19) and blowing it up considerably – is that a plume pointing out at about 11 o’clock in the middle white spot – center of dwarf planet? (I am referring to photo with the 2 views of Ceres, not the one with the 2 bright spots within the same crater.)

    • Andrew R Brown says:

      Hi Gary,

      I tried but I don’t think so. If anything it looks like a central peak of an impact crater. Any plumes at 1 Ceres will be extremely faint.

      We’ll see for sure when closer in.


  41. Andrew R Brown. says:

    Just what can I say ? Absolutely astonishing.

    The closer we get, the more 1 Ceres to me appears out of place within the Asteroid Belt, possibly more at home either in the Kuiper Belt or in orbit around Uranus or Neptune.

    That basin on the left image looks a lot like the Beethoven Basin on Mercury, largely smoother floor with newer superimposed impact craters like Bello Crater.

    Of course with Beethoven Basin, the impactor struck mercury’s dense crust, then volcanic lava flooded the basin, resurfacing and mostly filling it before cooling and solidifying.

    On 1 Ceres similar mechanism, but I assume cold cryolavas after the bollide struck an ice rich crust.

    Also I notice on both images a larger abundance of ‘double’ craters. Seen similar on 4 Vesta, 21 Lutetia and even on the vastly smaller 243 Ida and 253 Mathilde. Seems a higher prevalance than on the Moon, Mercury and Mars. Wonder if ‘double’ asteroids are more prevalent in the Asteroid Belt?

    Will be back for sure.

    Andrew R Brown. Ashford, Kent, United Kingdom.

  42. Matt Gibbons says:


  43. Corey says:

    Thanks for the deep and informative update. I’m wondering how much information you’ll be able to get about any organic compounds on the surface of Ceres from the VIR spectrometer. Will it be similar to the data coming from VIRTIS on Rosetta–ie, will you be able to deduce the presence of organics but not have enough data to define their precise species?

    • Marc Rayman says:

      Hi Corey,

      For others, VIR is Dawn’s visible and infrared mapping spectrometer.

      Yes, if there are organic materials on the surface of Ceres, we should be able to detect them but not determine the specific species. In order to answer your question about the comparison with the data from VIRTIS, a colleague on VIR looked into some of the details of the differences between the two instruments. Because dwarf planet Ceres is not at all like a comet, the instruments were designed to make different measurements, but she confirmed that for the most part, we can expect a similar level of detail.


  44. Luis says:

    Fantastic imagery, and journal update Marc! Now, some primary features are getting more clear. How lucky that apparently we have some “recent” (geologically speaking) impact craters, that perhaps will allow us to peek into and conduct spectral analysis on the strata composition of the most upper layer of Ceres “crust”? Some of the craters rim cliffs look like amazing to explore in the near future, as Dawn will stabilize into its final orbital paths, and higher resolution imagery and data will stream back to Earth.


    • Luis says:

      Image PIA19185_lg.jpg, seems to show, apart from the excitingly intriguing bright spots, what appears to be linear features (ancient fracture lines in the crust?), to the “SSE – image orientation wise” of the main center-image depicted crater.