Marc Rayman
Marc Rayman
Chief Engineer/ Mission Director, JPL
Dawn Journal | March 6

by Marc Rayman


Dear Unprecedawnted Readers,

Since its discovery in 1801, Ceres has been known as a planet, then as an asteroid, and later as a dwarf planet. Now, after a journey of 3.1 billion miles (4.9 billion kilometers) and 7.5 years, Dawn calls it “home.”

Earth’s robotic emissary arrived at about 4:39 a.m. PST today. It will remain in residence at the alien world for the rest of its operational life, and long, long after.

Before we delve into this unprecedented milestone in the exploration of space, let’s recall that even before reaching orbit, Dawn started taking pictures of its new home. Last month we presented the updated schedule for photography. Each activity to acquire images (as well as visible spectra and infrared spectra) has executed smoothly and provided us with exciting and tantalizing new perspectives.

While there are countless questions about Ceres, the most popular now seems to be what the bright spots are. It is impossible not to be mesmerized by what appear to be glowing beacons, shining out across the cosmic seas from the uncharted lands ahead. But the answer hasn’t changed: we don’t know. There are many intriguing speculations, but we need more data, and Dawn will take photos and myriad other measurements as it spirals closer and closer during the year. For now, we simply know too little.

Animated Gif

Dawn observed Ceres for a full rotation of the dwarf planet, which lasts about nine hours. The photos were taken on Feb. 19 from a distance of about 28,000 miles (46,000 kilometers). A single mosaic made from the individual pictures is below. The imaging session was known as RC2. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

For example, some people ask if those spots might be lights from an alien city. That’s ridiculous! At this early stage, how could Dawn determine what kinds of groupings Cereans live in? Do they even have cities? For all we know, they may live only in rural communities, or perhaps they only have large states.

What we already know is that in more than 57 years of space exploration, Dawn is now the only spacecraft ever to orbit two extraterrestrial destinations. A true interplanetary spaceship, Dawn left Earth in Sep. 2007 and traveled on its own independent course through the solar system. It flew past Mars in Feb. 2009, robbing the red planet of some of its own orbital energy around the sun. In July 2011, the ship entered orbit around the giant protoplanet Vesta, the second most massive object in the main asteroid belt between Mars and Jupiter. (By the way, Dawn’s arrival at Vesta was exactly one Vestan year ago earlier this week.) It conducted a spectacular exploration of that fascinating world, showing it to be more closely related to the terrestrial planets (including Earth, home to many of our readers) than to the typical objects people think of as asteroids. After 14 months of intensive operations at Vesta, Dawn climbed out of orbit in Sep. 2012, resuming its interplanetary voyage. Today it arrived at its final destination, Ceres, the largest object between the sun and Pluto that had not previously been visited by a spacecraft. (Fortunately, New Horizons is soon to fly by Pluto. We are in for a great year!)

What was the scene like at JPL for Dawn’s historic achievement? It’s easy to imagine the typical setting in mission control. The tension is overwhelming. Will it succeed or will it fail? Anxious people watch their screens, monitoring telemetry carefully, frustrated that there is nothing more they can do now. Nervously biting their nails, they are thinking of each crucial step, any one of which might doom the mission to failure. At the same time, the spacecraft is executing a bone-rattling, whiplash-inducing burn of its main engine to drop into orbit. When the good news finally arrives that orbit is achieved, the room erupts! People jump up and down, punch the air, shout, tweet, cry, hug and feel the tremendous relief of overcoming a huge risk. You can imagine all that, but that’s not what happened.

If you had been in Dawn mission control, the scene would have been different. You would mostly be in the dark. (For your future reference, the light switches are to the left of the door.) The computer displays would be off, and most of the illumination would be from the digital clock and the string of decorative blue lights that indicate the ion engine is scheduled to be thrusting. You also would be alone (at least until JPL Security arrived to escort you away, because you were not cleared to enter the room, and, for that matter, how did you get past the electronic locks?). Meanwhile, most of the members of the flight team were at home and asleep! (Your correspondent was too, rare though that is. When Dawn entered orbit around Vesta, he was dancing. Ceres’ arrival happened to be at a time less conducive to consciousness.)

Why was such a significant event treated with somnolence? It is because Dawn has a unique way of entering orbit, which is connected with the nature of the journey itself. We have discussed some aspects of getting into orbit before (with this update to the nature of the approach trajectory). Let’s review some of it here.

It may be surprising that prior to Dawn, no spacecraft had even attempted to orbit two distant targets. Who wouldn’t want to study two alien worlds in detail, rather than, as previous missions, either fly by one or more for brief encounters or orbit only one? A mission like Dawn’s is an obvious kind to undertake. It happens in science fiction often:  go somewhere, do whatever you need to do there (e.g., beat someone up or make out with someone) and then boldly go somewhere else. However, science fact is not always as easy as science fiction. Such missions are far, far beyond the capability of conventional propulsion.

Deep Space 1 (DS1) blazed a new trail with its successful testing of ion propulsion, which provides 10 times the efficiency of standard propulsion, showing on an operational interplanetary mission that the advanced technology really does work as expected. (This writer was fortunate enough to work on DS1, and he even documented the mission in a series of increasingly wordy blogs. But he first heard of ion propulsion from the succinct Mr. Spock and subsequently followed its use by the less logical Darth Vader.)

Cratered Surface at Ceres

Dawn observed Ceres throughout a full nine-hour rotation of the dwarf planet, yielding this global mosaic of craters, mysterious bright spots and other intriguing features. The photos were taken on Feb. 19 from a distance of about 28,000 miles (46,000 kilometers). Ceres has about 38 percent of the area of the continental United States. The imaging session was known as RC2. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

Dawn’s ambitious expedition would be truly impossible without ion propulsion. (For a comparison of chemical and ion propulsion for entering orbit around Mars, an easier destination to reach than either Vesta or Ceres, visit this earlier log.) So far, our advanced spacecraft has changed its own velocity by 23,800 mph (38,400 kilometers per hour) since separating from its rocket, far in excess of what any other mission has achieved propulsively. (The previous record was held by DS1.)

Dawn is exceptionally frugal in its use of xenon propellant. In this phase of the mission, the engine expends only a quarter of a pound (120 grams) per day, or the equivalent of about 2.5 fluid ounces (75 milliliters) per day. So although the thrust is very efficient, it is also very gentle. If you hold a single sheet of paper in your hand, it will push on your hand harder than the ion engine pushes on the spacecraft at maximum thrust. At today’s throttle level, it would take the distant explorer almost 11 days to accelerate from zero to 60 mph (97 kilometers per hour). That may not evoke the concept of a drag racer. But in the zero-gravity, frictionless conditions of spaceflight, the effect of this whisper-like thrust can build up. Instead of thrusting for 11 days, if we thrust for a month, or a year, or as Dawn already has, for more than five years, we can achieve fantastically high velocity. Ion propulsion delivers acceleration with patience.

Most spacecraft coast most of the time, following their repetitive orbits like planets do. They may use the main engine for a few minutes or perhaps an hour or two throughout the entire mission. With ion propulsion, in contrast, the spacecraft may spend most of its time in powered flight. Dawn has flown for 69% of its time in space emitting a cool blue-green glow from one of its ion engines. (With three ion engines, Dawn outdoes the Star Wars TIE — twin ion engine — fighters.)

OpNav 5 images zoomed in

As Dawn maneuvers into orbit, its trajectory takes it to the opposite side of Ceres from the sun, providing these crescent views. These pictures (part of the OpNav 5 activity), were taken on March 1 at a distance of 30,000 miles (49,000 kilometers). Image credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

The robotic probe uses its gentle thrust to gradually reshape its path through space rather than simply following the natural course that a planet would. After it escaped from Vesta’s gravitational clutches, it slowly spiraled outward from the sun, climbing the solar system hill, making its heliocentric orbit more and more and more like Ceres’. By the time it was in the vicinity of the dwarf planet today, both were traveling around the sun at more than 38,600 mph (62,100 kilometers per hour). Their trajectories were nearly identical, however, so the difference in their speeds was only 100 mph (160 kilometers per hour), or less than 0.3 percent of the total. Flying like a crackerjack spaceship pilot, Dawn elegantly used the light touch of its ion engine to be at a position and velocity that it could ease gracefully into orbit. At a distance of 37,700 miles (60,600 kilometers), Ceres reached out and tenderly took the newcomer from Earth into its permanent gravitational embrace.

If you had been in space watching the event, you would have been cold, hungry and hypoxic. But it would not have looked much different from the 1,885 days of ion thrust that had preceded it. The spacecraft was perched atop its blue-green pillar of xenon ions, patiently changing its course, as it does for so much of quiet cruise. But now, at one moment it was flying too fast for Ceres’ gravity to hang on to it, and the next moment it had slowed just enough that it was in orbit. Had it stopped thrusting at that point, it would have continued looping around the dwarf planet. But it did not stop. Instead, it is working now to reshape its orbit around Ceres. As we saw in November, its orbital acrobatics first will take it up to an altitude of 47,000 miles (75,000 kilometers) on March 18 before it swoops down to 8,400 miles (13,500 kilometers) on April 23 to begin its intensive observations in the orbit designated RC3.

In fact, Dawn’s arrival today really is simply a consequence of the route it is taking to reach that lower orbit next month. Navigators did not aim for arriving today. Rather, they plotted a course that began at Vesta and goes to RC3 (with a new design along the way), and it happens that the conditions for capture into orbit occurred this morning. As promised last month, we present here a different view of the skillful maneuvering by this veteran space traveler.

Dawn Ceres Trajectory

This animation gives a three-dimensional view of Dawn’s complex approach to Ceres. The spacecraft deftly maneuvers into orbit with its ion propulsion system, flying to RC3 orbit, which is achieved when the thrust is turned off. (The size of Ceres is exaggerated compared to the size of the orbit here.) At the end, the viewpoint shifts to provide another perspective on the unique trajectory.

If Dawn had stopped thrusting before Ceres could exert its gravitational control, it wouldn’t have flown very far away. The spacecraft had already made their paths around the sun very similar, and the ion propulsion system provides such exceptional flexibility to the mission that controllers could have guided it into orbit some other time. This was not a one-time, all-or-nothing event.

So the flight team was not tense. They had no need to observe it or make a spectacle out of it. Mission control remained quiet. The drama is not in whether the mission will succeed or fail, in whether a single glitch could cause a catastrophic loss, in whether even a tiny mistake could spell doom. Rather, the drama is in the opportunity to unveil the wonderful secrets of a fascinating relict from the dawn of the solar system more than 4.5 billion years ago, a celestial orb that has beckoned for more than two centuries, the first dwarf planet discovered.

Dawn usually flies with its radio transmitter turned off (devoting its electricity instead to the power-hungry ion engine), and so it entered orbit silently. As it happened, a routine telecommunications session was scheduled about an hour after attaining orbit, at 5:36 a.m. PST. (It’s only coincidence it was that soon. At Vesta, it was more than 25 hours between arrival and the next radio contact.) For primary communications, Dawn pauses thrusting to point its main antenna to Earth, but other times, as in this case, it is programmed to use one of its auxiliary antennas to transmit a weaker signal without stopping its engine, whispering just enough for engineers to verify that it remains healthy.

The Deep Space Network’s exquisitely sensitive 230-foot (70-meter) diameter antenna in Goldstone, Calif., picked up the faint signal from across the solar system on schedule and relayed it to Dawn mission control. One person was in the room (and yes, he was cleared to enter). He works with the antenna operator to ensure the communications session goes smoothly, and he is always ready to contact others on the flight team if any anomalies arise. In this case, none did, and it was a quiet morning as usual. The mission director checked in with him shortly after the data started to trickle in, and they had a friendly, casual conversation that included discussing some of the telemetry that indicated the spacecraft was still performing its routine ion thrusting. The determination that Dawn was in orbit was that simple. Confirming that it was following its flight plan was all that was needed to know it had entered orbit. This beautifully choreographed celestial dance is now a pas de deux.

As casual and tranquil as all that sounds, and as logical and systematic as the whole process is, the reality is that the mission director was excited. There was no visible hoopla, no audible fanfare, but the experience was powerful fuel for the passionate fires that burn within.

As soundlessly as a spacecraft gliding through the void, the realization emerges…

Dawn made it!!

It is in orbit around a distant world!!

Yes, it’s clear from the technical details, but it is more intensely reflected in the silent pounding of a heart that has spent a lifetime yearning to know the cosmos. Years and years of hard work devoted to this grand undertaking, constant hopes and dreams and fears of all possible futures, uncounted challenges (some initially appearing insurmountable) and a seeming infinitude of decisions along the way from early concepts through a real interplanetary spacecraft flying on an ion beam beyond the sun.

And then, a short, relaxed chat over a few bits of routine data that report the same conditions as usual on the distant robot. But today they mean something different.

They mean we did it!!

Everyone on the team will experience the news that comes in a congratulatory email in their own way, in the silence and privacy of their own thoughts. But it means the same to everyone.

We did it!!

And it’s not only the flight team. Humankind!! With our relentless curiosity, our insatiable hunger for knowledge, our noble spirit of adventure, we all share in the experience of reaching out from our humble home to the stars.

Together, we did it!!!

It was a good way to begin the day. It was Dawn at Ceres.

Destination Dwarf Planet: The Dawn Mission Nears Ceres

This video overview of the mission at Ceres is a great way to start your day, but you can enjoy it at any time.

Let’s bring into perspective the cosmic landscape on which this remarkable adventure is now taking place. Imagine Earth reduced to the size of a soccer ball. On this scale, the International Space Station would orbit at an altitude of a bit more than one-quarter of an inch (seven millimeters). The moon would be a billiard ball almost 21 feet (6.4 meters) away. The sun, the conductor of the solar system orchestra, would be 79 feet (24 meters) across at a distance of 1.6 miles (2.6 kilometers). But even more remote, Dawn would be 5.3 miles (8.6 kilometers) away. (Just a few months ago, when the spacecraft was on the opposite side of the sun from Earth, it would have been more than six miles, or almost 10 kilometers, from from the soccer ball.) Tremendously far now from its erstwhile home, it would be only a little over a yard (a meter) from its new residence. (By the end of this year, Dawn will be slightly closer to it than the space station is to Earth, a quarter of an inch, or six millimeters.) That distant world, Ceres, the largest object between Mars and Jupiter, would be five-eighths of an inch (1.6 centimeters) across, about the size of a grape. Of course a grape has a higher water content than Ceres, but we can be sure that exploring this intriguing world of rock and ice will be much sweeter!

As part of getting to know its new neighborhood, Dawn has been hunting for moons of Ceres. Telescopic studies had not revealed any, but if there were a moon smaller than about half a mile (one kilometer), it probably would not have been discovered. The spacecraft’s unique vantage point provides an opportunity to look for any that might have escaped detection. Many pictures have been taken specifically for this purpose, and scientists scrutinize them and all of the other photographs for any indication of moons. While the search will continue, so far, no picture has shown evidence of companions orbiting Ceres.

And yet we know that as of today, Ceres most certainly does have one. Its name is Dawn!

Dawn is 37,800 miles (60,800 kilometers) from Ceres, or 16 percent of the average distance between Earth and the moon. It is also 3.33 AU (310 million miles, or 498 million kilometers) from Earth, or 1,230 times as far as the moon and 3.36 times as far as the sun today. Radio signals, traveling at the universal limit of the speed of light, take 55 minutes to make the round trip.

Dr. Marc D. Rayman
6:00 a.m. PST March 6, 2015

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115 Responses to “Dawn Journal | March 6”

  1. Thanks for this fascinating mission –and your Dawn blog, Marc. I did some screen captured stereo pairs on those bright spots –at:


    Might the bright one be some kind of a crystalline blob –imaging the Sun on the crater wall?

    Craig (you have full permission to copy/re-use my graphics work –of course)

  2. Charlie Ryan says:

    Hi Marc,

    Love the blog, find your dedication to responding to every comment truly astonishing!
    My Q is a little left field. I’m a research engineer working on electric propulsion at Surrey University, UK. We are design an exhibit stand to talk about our research at a large outreach event, open to members of public – 15,000 people in a week!
    We would love to have an interactive element on the stand that showed how ion thrusters work in a really simple manner, but are struggling to come up with anything workable. Do you have any ideas from your (very!) large outreach experience?
    We were thinking about polystyrene packing beads in a container on the top of a Van de Graaf generator, which can be like the xenon getting charged and thrown out of the thruster. But this has proved tricky to do, and keeps electrocuting me!
    So if you, or anyone else out there has any ideas that would be much appreciated. Thanks!

    Charlie Ryan

    • Dawn Education and Communications says:

      Dear Charlie,

      Marc appreciated your comment and passed your question to me because of my work in education and communication. Great that you are trying to come up with ways to help your public conceptualize ion propulsion. Creating macroscopic models for phenomenon at the molecular scale is a fine way to step learners from concrete to abstract understanding.

      I wanted to be sure you were aware of some resources that illustrate ion propulsion among Dawn resources that might be useful in your quest.
      Crazy Engineering is a video developed by Jet Propulsion Laboratory that highlights ion propulsion (and stars Marc Rayman ;]).
      Ion Engines offers a set of resources and activities, including a simple interactive game that helps learners gain an intuitive understanding of the forces involved in ion propulsion, and an invitation for them to develop their own Ion Engine Interactive.

      Best to you and your endeavors,

      Dawn Education and Communications

      • Charlie Ryan says:

        Hi Whitney,

        Thanks for your advice, I have seen the video and app, both look great. Would it be possible to use the interactive game on some tablets on our outreach stand? We would of course state that the game is from JPL/NASA, and provide whatever further credit is necessary.
        Also if you have any further ideas, especially of how to make some interactive hands-on element that gives people a rough understanding of how ion thrusters work, that would be most appreciated!
        Thanks for your time

        • Whitney says:

          Hi Charlie,

          I don’t know if the game is usable on mobile formats, it was developed before that was part of our collective lexicon, so I doubt it, but I will look into it. If it is workable, I don’t see a problem using it on your outreach stand – it is open source and we want it to be used! And I will noodle on a back burner on ion propulsion, hands-on models and ask colleagues as well. Every once in a while, the light bulb flashes.


          • Charlie Ryan says:

            Hi Whitney,

            I think it should be possible to sort of cache the java game on a website, on which we can hide most of the other links. If we work out a good way to do this, we will let you know; i guess it might be useful for you as well.

            Thanks for your time again,

  3. Anthony P. says:

    Hello Dr. Rayman,

    Only the utmost of respect for taking the time and maintaining this blog series with many educational links and science facts that give the first glimpse to people outside of space exploration and -for me specifically- intrigue us to learn more and follow new missions consistently.

    A few questions:
    1) Using available imaging techniques, is it possible to infer if these bright spots that create the strong reflection come from a higher altitude from the ground or are they part of the surface? We probably should wait for the first images from OpNav 6 to get a better understanding?
    In the same context, have we ever encountered similar reflections of spots on other missions to planets/asteroids in our solar system? That would give us a good clue into what we are actually observing here.

    2) An interesting observation from a previous commenter was that most of the craters on Ceres surface seem to be shallow (or probably we are looking at them from a great distance :)) and we can actually see some less reflective spots which are more scattered and of a bigger reflective area but not that bright.
    Is it possible that Ceres is actually made of a more concrete and reflective layer just a little bit underneath the surface which would produce exposure of it on bigger craters and various parts of the planet?

    Thank you *a lot* and many wishes for this continuous mission :)


  4. Barry Curtis says:

    I am studying the video clip of the rotation of Ceres and I clearly see the larger of the two lights still illuminated well past the line of darkness. I would estimate that it about halfway from where the darkness starts to the outer edge of the circumference that is completely shrouded in darkness. It’s also interesting that the many craters are all shallow in depth. There appear none that are exceptionally deeper than others. Makes me wonder how hard the surface of Ceres is.

  5. Guillaume Vollant-Boulé says:

    Hello Dr. Rayman,
    would it be possible that Dawn go directly to a lower orbit, instead of looking at Ceres and using hydrazine? In other words, skip the HAMO and LAMO to go directly in a hypothetical SLAMO at about the same altitude as Dawn did his LAMO at Vesta and would that be scientifically useful? And if this question as already been answered, don’t bother doing a personalized answer, as your spare time right now is small, a link to a previous answer will suffice.

    Thank you,
    Guillaume Vollant-Boulé

    PS: Sorry to ask questions in such a disorganized manner, but they come to me as I go with my search for information in the fantastic world of space exploration.

    PPS: Also, sorry to ask them only to you. I would love to ask them to somebody else to release you of some workload

    • Marc Rayman says:

      Hi Guillaume,

      For others, the acronyms Guillaume uses refer to the two lowest altitude mapping orbits at Ceres. HAMO is described here and LAMO here. I plan to summarize all four planned mapping orbits in my next Dawn Journal. SLAMO was my fanciful term for an unplanned super low orbit.

      There are two very practical engineering and science reasons Dawn cannot go directly to a lower orbit at Ceres. (These same reasons applied at Vesta.)

      The first is that we do not know enough about the Ceres gravity field. Dawn orbits massive bodies that have never been visited by a flyby spacecraft first. (I have written a few times about the why the gravity fields of Vesta and Ceres are not likely to be simple. See here for one example.) So we have to discover the details as we go. We fly in a little, measure the gravity field, then fly in a little more, etc. Our extensive mathematical analyses show that we cannot be confident in learning about the irregularities of the gravity quickly enough to fly directly to a low orbit. I wrote last month that we have to bootstrap our way in, and the lower we go, the more difficult that is. We cannot acquire sufficiently detailed gravity knowledge without pausing the descent for a while. So as we are collecting data with Dawn’s instruments in each of the mapping orbits (starting with RC3 next month), we are also refining the measurements of the gravity field and then using them to design the spiral down to the next altitude.

      The other reason is that if we went directly to a low orbit, it would be significantly more difficult to make all of our planned measurements and more costly in hydrazine. Think of trying to map an area the size of Ceres. The closer you are, the longer it takes to see the entire surface. In RC3, as I will explain in my next Dawn Journal, we will map the entire surface in three imaging sessions spanning about a week. I described here that in the lower altitude HAMO, Dawn will complete a map in a dozen revolutions of 19 hours each, or 9.5 days. As I also explained there, we want to map the surface up to six times, each time at a different angle, to obtain enough stereo pictures to make topographical maps. As a result, we will stay at that altitude for more than two months. But in the lowest altitude orbit, the instruments see such a small portion of the surface that it will take more than 3 weeks to make a single map with the camera. In fact, the area viewed by both the infrared and the visible mapping spectrometers is so small that we will obtain nearly complete surface coverage only at the first two mapping orbit altitudes (RC3 and survey). At the third and final altitudes (HAMO and LAMO), we will observe only selected portions of the surface.

      As usual, there are many subtleties, but I hope this brief overview answers your questions.

      I greatly appreciate your concern for my time. As I’ve written, I understand the yearning for information, and I do what I can to share as many of the fascinating aspects of this mission as I can.


  6. Gavin says:

    Another space-geek here following Dawn’s historic exploration of Ceres with great excitement.

    I realize that right now you guys are in low activity mode as Dawn approaches for closer runs on Ceres, but the lack of information updates on the site is leaving this space-junky very parched. Any update, even if nominal, like a status update on telemetry or something, speed, approach, range, next maneuver planned, ect, say at a frequency of at least every 5 days, would greatly increase the traffic and interest to your site! Updated photographs, on a more timely basis, would also be received with thunderous applause.

    Thanks and keep up the great work!

    • Marc Rayman says:

      Hi Gavin,

      As a lifelong space geek, I’m glad to know you’re following the mission.

      We are most certainly not in a low activity mode. Indeed, by coincidence, this is among the busiest times of the year! Dawn, of course, is almost always busy, whether it is maneuvering with its ion engine, collecting data, or doing something else. (In fact, see more about this here.) But the operations team is very busy as well. We have been working hard on updating the ion thrust flight plan to guide the spacecraft precisely to RC3 orbit, on putting the finishing touches on the detailed instructions it will use to execute OpNav 6 and 7, and on working out many of the final aspects of the very complicated RC3 activities. We combine sets of instructions, timed down to the second, into what we call a sequence, and it takes a great deal of effort to develop, check, and double check them. I believe (although I haven’t reverified it recently) that of the entire Ceres mission, we have more sequences in development right now than we will at any other time. We also are often monitoring telemetry and then analyzing it to ensure the spacecraft is healthy. You cannot tell from what the spacecraft is doing how busy the team is.

      I do what I can to keep people informed, but I am simply too busy to post routine status updates. All of the material here is a result of my devoting my spare time, quite apart from my official JPL/NASA responsibilities, to sharing this adventure with space geeks like you and me. It is already very difficult for me to do as much as I do, and I am not able to do more. If that means that there is not as much traffic or interest in the site as there otherwise might be, I accept that (with regret). At Vesta, I wrote a status update just about every week, and you can see them here and here. Alas, now, with all the questions posted on this blog (many of them requiring me to repeat answers I’ve given several times already), I am very disappointed that I don’t even have time for that.

      You can get an idea of the speed and range by consulting the simulator here. (Please note that it is approximate!) Dawn maneuvers with its ion engine most of the time, as I have explained in many Dawn Journals, so it would not be meaningful to describe the next planned maneuver. Most spacecraft coast most of the time. Dawn has thrust for 70 percent of its time in space.

      Updated photographs are already provided on a timely basis. As I explained in detail in January and February, and in many of the comments below (see the thread here and the links in it), Dawn does not take pictures between March 1 and April 10.

      I’m glad to know you are so interested, and I understand very much what it is like to have an insatiable appetite for this sort of thing. That’s why I invest the effort I do here, but I recognize it is not as much as it could be. Still, I have written 111 Dawn Journals in an attempt to bring readers along on every aspect of this bold expedition from well before launch up to where we are now. (I also wrote two other blogs, and a few other members of the project have written blogs as well. See the links on the left.) While you’re waiting for the next installment, I invite you to look through some of them to keep your hunger at bay.

      Thank you for your interest!


      • Gavin says:

        Thanks Marc!

        I understand you not having time, and really, was shocked to see the team lead actually doing the updates! It’s unfortunate that you are forced to do this off the corner of your desk, and do not have a dedicated web team liason who is mainly responsible for web updates, paid for by JPL/NASA.

        In the current age of Instant Information, it is necessary, and important, to engage the public constantly to keep them focused on the importance of space exploration and scientific advancement, and this requires JPL/NASA to fund the appropriate resourcing.

        All the best and looking forward to some close-ups of those Cerean bio-domes reflecting all that sunlight! ;)


        • Marc Rayman says:

          Hi Gavin,

          JPL/NASA certainly recognizes both the value and the importance of engaging the public. That interest has allowed us to make the fun (I hope) Breakfast at Dawn video above, the cool animation of Dawn’s amazing approach trajectory above that, a neat video about ion propulsion, and more good things to come.

          Dawn has a team of dedicated professionals responsible for educational products and activities and for public outreach. These terrific folks have built a devoted following by tweeting and sharing news on Facebook, and they also do all the work here on the website. I enjoy working with them. If you had to count only on me to be responsible for the web updates, you’d really be starving! I enjoy giving the outside world an inside view of this exciting adventure and am only one of many engineers and scientists who voluntarily contribute to Dawn’s outreach efforts.

          Once again, I understand your desire to have as much as possible. People like you and me just can’t get enough. Still, I think the spacecraft’s remarkable exploits far, far from home plus the tremendous pictures and other findings it sends us will prove to be quite rewarding for all of us. I’m glad you’re along to share in this bold expedition.


  7. John Blazy says:

    Hi Dr. Rayman,

    Been following your blog, getting more excited as Dawn gets into closer orbit – Thanks a ton!

    My big issue is that the light source from the bright spots on Ceres are clearly SOURCED at the spots, NOT from sunlight reflected off of ice inside those craters as many have presumed, because the spots are visible even when they have rotated into Cere’s shadow – elementary physics, therefore this should be obvious.

    Since the only possible source can be photon generation via intense heat, which flies against the ice mantle theory, isn’t it possible that a magma tube from a molten core could form THROUGH the ice via the Leidenfrost effect where the ice surrounding the approaching lava becomes an insulating vapor barrier (on a macro scale) to allow a lava tube to form until it reaches the surface, giving off those photons?

    Im not a geologist, just a glass manufacturer that follows cool space sites like yours, but I am stumped as to why a recent youtube video stated that the prevailing theory for the two spots is ice reflection, which would be impossible when Ceres is in shadow.

    • Marc Rayman says:

      Hi John,

      I appreciate your enthusiastic interest!

      I have addressed this before. Please see this comment and the links in it. The spots are indeed reflected light. It is very difficult to see that in the animation that has been released, but there is no question about it. The planetary geologists who analyze the image data in great detail have no doubt about this. Eventually, as with the Vesta data, when the science team has completed preliminary analyses and interpretations, all of the original data will be available. For now, however, I will reassure you that the careful and quantitative examination shows that when the features are in shadow, they are no longer visible. They are very intriguing, and it is not yet clear what they are, but they are not sources of light.

      I’m glad you follow this cool mission, and before long we will all find out what those spots are, just as we will discover and understand many other features yet to be seen clearly. We have much to learn from Ceres, and I’m confident that your growing excitement will be well rewarded!


      • John Blazy says:

        Thank you for your reply and link to a better explanation – I will buy that theory now. Your clarification makes me wonder all the more about what kind of insanely beautiful ice crystals must be forming in order to have such a wide specular reflection range, so much so that it still reflects when nearing shadow.

        When Dawn nears the end of its service life, and is expendable, I hope you intentionally crash it into those spots taking pics the whole way down. Then we will know for certain (maybe).

        • Marc Rayman says:

          You are very welcome, John.

          It remains to be seen whether those spots really are ice, but I’m sure the sharper views will prove quite beautiful.

          As I explained here, we definitely will not allow the probe to reach the surface during its service life or long after. You can read about the reason and the ultimate fate, but in brief, Ceres is too important and interesting to be contaminated with our terrestrial materials. But we will gather a wide range of exquisite data before then. I think it’s quite likely the nature of the spots will be evident from our planned observations with the camera and all the spectrometers.


  8. Tim G says:

    Marc, the MYSTIC simulator indicates that Dawn’s
    specific orbital energy, v^2/2 -GM/r, has been creeping up.

    I noticed that it dipped below zero on March 6th when the mission
    planners celebrated Dawn’s capture.

    Is this related to saving time because saving xenon propellant isn’t the only issue?

    • Marc Rayman says:

      Hi Tim,

      For others, the specific orbital energy may be thought of as a measure of how firmly Ceres’ gravitational hold embraces Dawn. At higher energy, Ceres’ grip is weaker (because of the combination of Dawn’s altitude and velocity), and if the energy were high enough, Dawn would escape. Indeed, that is exactly how it departed from Vesta. To get into orbit, Dawn had to lower its energy enough that Ceres could take hold. To go to still lower orbits, it needs to reduce its orbital energy even further. This may not be easy to understand, and there are many subtleties here, but even if this isn’t entirely clear, read on, and you will understand the issue Tim is asking about. Rest assured, however, that Dawn is securely in orbit and is not going to leave. (So its orbital energy will remain negative.)

      You are quite right that the energy is increasing, and the reason is just as you wrote. I explained it in more detail in November. To summarize, Dawn would naturally fall toward Ceres after reaching the high point of its elliptical orbit (for a little more on this specific behavior, see the third paragraph of my comment below), but we use the ion engine to accelerate toward Ceres even faster. We have plenty of xenon and there is no need to conserve it this late in the mission. So we reduce the time it takes to travel to lower altitude (which is part of what we have to do to reshape the orbit into RC3) by propelling the spacecraft toward it. You can also see this in the animation above of the approach trajectory. Note how the thrust does not reverse quite when Dawn reaches that maximum orbital altitude. Rather, the ion beam is still directed away from Ceres, meaning the ship is still pushing itself toward Ceres. Only after it has accelerated its descent does it thrust in the reverse direction to brake smoothly into its low, circular orbit.

      I hope this answers your question and isn’t too confusing for others. I apologize for not having time to explain this more clearly.

      By the way, mission planners were not the only ones who celebrated Dawn’s capture :-) Indeed, comments below suggest some of our readers here joined in the celebration, which pleases me very much. I hope you might have felt some of the excitement as well! Thank you for your interest.


  9. Guillaume Vollant-Boulé says:

    Hello Dr. Rayman,
    I know you must be getting tired of my questions, but why did NASA prefer a «Electrostatic ion thruster» instead of a «Hall effect thruster».

    Thanks again,
    Guillaume Vollant-Boulé

    • Marc Rayman says:

      Hi Guillaume,

      I appreciate your questions, because they illustrate your interest in this exciting adventure. As I have written often (including below), however, my time for answering questions is pretty limited. So as long as you aren’t tired of delayed responses or answers that may be less clear or less thorough than you might prefer, it’s fine!

      For others, what Guillaume refers to as an “electrostatic ion thruster” is the ion engine used on Dawn. (The engine is the most visible part of the ion propulsion system, and I described a little about it here.) A Hall effect thruster is a related technology. Dawn uses the design that was so successfully tested on Deep Space 1, the first interplanetary mission to use ion propulsion. In brief, the combination of efficiency (what experts call specific impulse) and lifetime (measured by how much propellant it can reliably expend) made it very clear that this was significantly better than the alternatives. There simply was no other system that was qualified for operational use that could come close to the performance of this design.


  10. todd pattison says:

    Hello Mark,
    I have a few curious questions, first, what were the factors in deciding to use this craft with its new ion drive to travel to Ceres, and were there any other candidates. Second, when will we be given more information on the two bright spots and how long has NASA been aware of them. Third will this craft remain around Ceres for its entire life span? it is a beautiful craft draped in its golden sheath named dawn.

    • Marc Rayman says:

      Hi Todd,

      I appreciate your new interest in this grand adventure. I have addressed some of this before, so I will be very brief now.

      Dawn’s ion drive is uniquely capable and very cool, but it is not new. The first interplanetary spacecraft to use ion propulsion was Deep Space 1, and it paved the way for Dawn’s more ambitious mission. I explained in December what makes Ceres so fascinating and why we want to explore it. As for other candidates, I don’t know whether you mean other candidate destinations to explore or other candidate spacecraft to explore Ceres. NASA is interested in many destinations throughout the solar system, and I regret I cannot take the time to delve into other missions or other mission proposals here. I have described many times that a mission to orbit even just one of Dawn’s two destinations would have been unaffordable in NASA’s Discovery Program without ion propulsion, and a mission to orbit both would have been truly impossible. So if we want to explore Ceres (and by golly we do!), ion propulsion makes it practicable.

      Dawn will resume taking pictures in April, and I gave the detailed schedule last month. The spacecraft is maneuvering now into its first mapping orbit and will return better pictures of the bright spots in early May. I gave a preview of that mission phase here, and I plan to write more about it in my next Dawn Journal. You can see a bright spot in pictures from Hubble Space Telescope taken more than a decade ago. It was not until last month that Dawn acquired pictures sharp enough to reveal that the bright spot actually consists of two smaller spots. I don’t know what we will find when we get still better resolution.

      Dawn will remain in orbit around Ceres for the rest of its life and for long, long after. You can read about that in my August Dawn Journal.

      I hope these very short answers satisfy your curiosity and that you continue to follow Dawn. We are all curious to see what secrets Ceres hold, and it will be exciting to discover the answers together.


  11. Stephen Verba says:


    As a teen in the mid 60’s I recall visiting NASA event here in Cleveland where there was a booth on propulsion. I have a picture of me standing there talking to two NASA engineers asking them when they might shift to using cesium ion engines. My recollection is that they seemed to look at each other rather wistfully…your fine blog provides a great explanation of the merits of ion propulsion and celebrates its success on this incredible mission

    Just out of curiosity, whatever ever happened to using cesium (vs xenon)?


    • Marc Rayman says:

      Hi Steve,

      It’s neat that you’ve been interested in ion propulsion for so long.

      Many of the technical underpinnings date to even the 1960s. Cesium was one of the propellants used in early tests. Mercury was another. They presented a number of difficulties. One is that they required heating just to turn them into gas to feed to the engine. Also, even the tiny amounts that escape from the engine at low velocity can contaminate sensitive components on the spacecraft, including optical sensors and solar cells. Xenon solves those and other problems.


  12. John Willis says:

    I was just playing with my Canon G10 camera and noiticed a reflection off the lense that looks remarkably like the two lights in the crater.

    The bright spot was from the reflection off the top of the dome of the lens, the second bright spot off center seemed to be because the lamp was not directly over the top.

    I noticed when Ceres rotated in the image the second light dimmed in the same way.

    I doubt there’s a transparent dome on Ceres, but maybe a frozen umbrella of ice that spewed up real slow and stopped like those ice sculptures you get when a fountain freeze on a cold Dallas Texas morning?

    Seems like there were Sulphur volcanoes kind of like that on Io near Jupiter.

    • Andrew R Brown says:

      Hi John Willis,

      Great post.

      I wonder if it is still a peak with fresh landslides with the secondary spot being another landslide on the crater wall.

      You are largely correct about the Jupiter moon Io, though the volcanic plumes are not static, but they are permanently positioned over volcanic craters and lava lakes, giving an overall impression of being ‘frozen’ in place.

      Here is Tvashtar Volcano on Io, with a short movie put together from the Pluto bound New Horizons spacecraft. The fountain nature is very evident.

      Andrew R Brown. Ashford, Kent, United Kingdom.

  13. Andrew R Brown says:

    Hi Marc,

    I assume that DAWN has passed the first apoapsis around 1 Ceres and is starting to very slowly approach the protoplanet again?

    Is the current position and Ion thrusting of DAWN being monitored through the auxiliary Low Gain antennas?

    Also during approach and post orbital insertion, how accurate was the prearrival assumed mass of 1 Ceres?

    I think the bright spots are still ‘recent’ landslides exposing unaltered un space weathered material on the crater peak and on the crater wall.

    the ‘grooves’ in the southern hemisphere I think at the current time are a greater mystery, though I think they are either due to slowing of the rotation of 1 Ceres causing the oblateness to reduce, putting pressure on the crust and / or crater chains from an impact near the south pole of 1 Ceres.

    Andrew R Brown. Ashford, Kent, United Kingdom.

    • Marc Rayman says:

      Hi Andrew,

      For others, apoapsis is the most distant point of an elliptical orbit. (The term “apogee” may be more familiar. That is the most distant point in an elliptical orbit around Earth. Apoapsis is more general, applying to orbits around anything.)

      As I described in my Dawn Journal above, Dawn reached that highest altitude on March 18, so, yes, its orbit is now taking it closer to the dwarf planet again. I wrote more about this below. (As I know you follow the mission with great interest, perhaps you had already read about that, even as long ago as November, in which case perhaps I should reassure you that I whenever there are significant changes to the mission, I present updates as soon as I have time to do so.)

      As I also wrote in my Dawn Journal above (and many other times, including here), the spacecraft usually flies with its radio transmitter off. So most of the time, we do not monitor it. We have 7.5 years of flight experience with this sophisticated probe, and 5.2 years of that time has been spent in powered flight. We have high confidence in this reliable robot. (Just as on Deep Space 1, the first interplanetary mission to use ion propulsion, we never intended to observe thrusting all the time. It’s unnecessary, and there are technical and financial reasons not to.) We usually program it to turn on its transmitter twice a week. Sometimes we use the auxiliary antenna while it is ion thrusting, and other times the instructions call for it to stop thrusting and rotate to point its main antenna to Earth. (You can see those short periods of coasting in this diagram from last month.)

      As I commented below, I will provide an update on the mass of Ceres in May. This will give you something else to look forward to! :-)


      • Andrew R Brown says:

        Thank You very much Marc,

        One thing I think that could be attempted is whether or not DAWN could be tracked for the last few hours prior to RC3 to measure the shape of the inner gravity well using the auxiliary Low Gain antennas to assist determining whether or not 1 Ceres is internally differentiated like Ganymede or Dione, or whether a homogenous, mixed interior like Callisto, Titan or Rhea?

        Also would it not be possible to extend OpNav 7 to a full rotation? 49% illumination @ 2.1 KM resolution would be awesome. OpNav 7 would become RC 3 and RC 3 orbit would become RC 4 orbit.

        Andrew R Brown. Ashford, Kent, United Kingdom.

        • Marc Rayman says:

          Hi Andrew,

          Rather than track Dawn while it is ion thrusting, we will track it with one of the auxiliary antennas throughout all of the mapping orbits. We did the same thing at Vesta (which is how we learned about the interior structure of that protoplanet). I have described this in several Dawn Journals, including here.

          I won’t take the time here to go into detail, but tracking Dawn while it is ion thrusting does not yield as much insight into the gravity field as when the spacecraft is coasting. Moreover, even tracking Dawn for more than two weeks in RC3 orbit will not be sufficient to determine the detailed gravity field. It will help, but the lower altitude orbits provide a much better view of the interior.

          We will get plenty of awesome data in our RC3 orbit with pictures 1.7 times sharper than OpNav 7. OpNav 7 cannot substitute for RC3, because OpNav 7 occurs high over the northern hemisphere. Only a portion of Ceres would be visible. RC3 will cover the entire surface. The objective of OpNav 7 is to provide important navigation data needed to achieve a good orbit for RC3, where we have plans for extensive observations, as I explained here (and I will write about it in more detail in my next Dawn Journal). It would not be wise to give up valuable time that could be spent thrusting to reach RC3 (by extending the duration of OpNav 7 plus the telecommunications session required to transmit additional pictures) and to expend precious hydrazine.


          • Andrew R Brown says:

            Thank you very much Marc,

            You must be getting fed up with me keep posting on here :D

            I was not aware of the viewing geometry regarding the rotational axis of OpNav 7. One thing though, it will be a great early view of the far north of 1 Ceres and will assist mapping of the north polar Asari Quadrangle and the Chahal, Dagau, Ebisu and Gurcho quadrangles in the northern hemisphere of 1 Ceres.

            First preliminary maps.


            Image Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA. Emily Lakdawalla.

            Would it be possible to see a third one with a visual photographic map?

            This is getting better all the time :)

            Andrew R Brown. Ashford, Kent, United Kingdom.

            • Marc Rayman says:

              Hi Andrew,

              I’m delighted with your interest and your enthusiasm. Post as much as you like that’s related to Dawn and its mission, and I hope others will as well. As you so correctly observed here, this is a serious (well, mostly) blog, and I want you and others to enjoy the richness of this mission, with its amazing scientific discoveries, its extraordinary technical accomplishments, and its simply awesome spirit of adventure! I only hope everyone will understand if I don’t reply to every post or sometimes reply late. My technical responsibilities keep me busy. I am not very good at keeping up with the many questions people ask as well as my other outreach work (including writing the Dawn Journals), all of which I do in what would be my free time.

              I will show the viewing geometry again in my next Dawn Journal. In the meantime, you can get a sense of Dawn’s position over the northern hemisphere late in the approach phase (specifically, OpNav 7) from some of the material in November (including the second of the two trajectory diagrams) and February. You also might be able to see it in the trajectory animation above, noting where Dawn is on April 14. Nevertheless, I recognize that it is difficult to get a good perspective, and none of this is intuitive. The approach trajectory is very complicated. But you can (if you wish) take my word for it that we won’t give up any worthwhile opportunities to squeeze as much out of the Ceres mission as we can (just as we did at Vesta), given the myriad constraints.

              The links you gave are not maps. They are mapping regions, chosen even before we saw anything on Ceres. The science team includes a group of expert geological mappers, and they have divided up the responsibility for mapping this new world simply on the basis of latitude and longitude, as shown in your first link. We did the same thing at Vesta, and then the final results were integrated into the beautiful result shown here. The mosaic shown in my Dawn Journal above is the most complete view we have so far.

              I agree with you it is getting better all the time. I think it’s pretty cool already, and we have a great deal more to look forward to!


  14. Andrew BROOKS says:

    G’day Marc

    For long time, probably for 2 years now, that I have been fascinated about your daily ‘View of Ceres from Dawn’ snapshot. Whats troubled me is the meaning of ’30 degree view’ heading. Does that 30 degrees represents Dawn spacecraft flying 30 degrees above or below Ceres from Earth’s orientation or perspective?

    Please enlighten me!

    By the way, it is interesting to see how the stars in the background of this craft have shifted quite dramatically in the last 10 days due the craft slowly easing and curving into an orbit of this little planet. The speed of this craft relative to Ceres is still dropping and as I write it is now 40mph at the distance 48.3 thousand miles. When will this craft will be at its slowest speed and how far will it be from Ceres? Absolutely fascinating I must say!

    Andrew BROOKS (Sydney)

    • Marc Rayman says:

      Hi Andrew,

      The 30 degrees for Where is Dawn Now? is the width of our viewpoint in looking at the simulator. It has nothing to do with Dawn’s trajectory but rather with how wide the picture is. I’ve asked my (busy) friend and colleague who maintains the Where is Dawn Now? simulation to give me some additional details to broaden my answer, and I will post an update here when he has time.

      In the meantime, I should caution you that the simulator has a few quirks. In addition, he doesn’t always have time to incorporate the most up to date trajectory design, so you should be cautious about using it for detailed quantitative purposes. The numbers are close, but the distance indicated now is actually higher than the real value (and the speed is a little lower than what’s shown), as will be evident in the remaining part of my answer…

      Although the spacecraft is thrusting with its ion propulsion system, so its orbit is constantly changing, in one regard you can think of it as being like a ball thrown high (and if your ball has ion propulsion, it’s even more like Dawn). As it ascends, gravity slows it down. If you throw it straight up, at the top of its arc, it momentarily stops and then reverses direction, falling and speeding up as it succumbs to the relentless pull of gravity. Dawn’s trajectory is more complicated, but the same basic behavior occurs. As I mentioned last month and again above, the peak of its arc will be on March 18 PDT at a height of about 47,000 miles (75,000 kilometers). It will gradually cease its upward motion relative to Ceres, neither approaching nor receding, and then just as gradually accelerate as Ceres and the ion engine together send it down to lower and lower altitude.

      Now although it stops climbing away from Ceres and begins approaching again, Dawn is also moving around Ceres, because it is in orbit. (That is, we didn’t throw the ball straight up but rather gave it forward momentum as well.) So it doesn’t actually come to a full stop. Rather, near the crest of its orbit, the spacecraft will slow down to around 35 mph (56 kilometers per hour).

      For those who want to get a more visual sense of what’s occurring, watch the animation above again as Dawn banks into orbit.

      I hope this explanation is helpful.


      • Leonard Cottrell says:

        If only your friend and colleague with the view simulator were not so busy, he could now include the disk of Ceres in the fullview1 which is centered on the Sun.
        Fullview1 shows the two shoulder stars of Orion near the bottom edge right above where the speed rel Sun is given as “17.23 km/s”
        and fullview2 view shows Ceres near the shoulder star on our left.

        If your friend were to put Ceres in the fullview1 picture it would, I estimate, be right behind the numeral “1” in “17.23 km/s”.
        A shadowy disk which only people who took the trouble to look for it would notice.

        I was very glad to read what you said about achieving turnaround by 18 March at 75 kkm distance still with a sideways speed of 35 mph—and wish you and colleagues bon voyage on the dive back towards the sweet icy planetto.

  15. Simon Jensen says:

    Hi Marc,

    thanks for your extracurricular activities, this blog is tremendously helpful and totally inspiring!

    In your answer to Mr. Brooks from Sydney, you point out that the bright spots have perhaps the same brightness as the average surface of Vesta, but that they stand out in terms of contrast to the rest of Ceres surface. does this mean that the average surface of Ceres is very dark? Does a darker surface mean that the material is heavy rock? And if so, does rocky material then point to a different origin of the material, of which it is composed of?. To what extend will the instruments on-board DAWN be able to determine the composition of material?

    (There was at least one video on this site, where it was said that Ceres’ material supposedly origins from the “Dawn” of the Solar system. The material thus, was supposed to be light, like gases and water. But fx. the Rosetta orbiter likewise found an extremely dark, rocky almost coal-black Comet 67P which I believe was contrary to prediction.)

    Another question, once in orbit, how do you go about mapping Ceres, will Dawn have an orbit that allows it to frequent the bright spot more often or is there even something like a geostationary spot to hang out in?.

    Once again, thanks for sharing and spreading excitement and for your time.
    Much appreciated!


    • Marc Rayman says:

      Hi Simon,

      Thank you for your kind message!

      The comment you refer to is below. The average surface of Ceres is indeed dark. As I mentioned in that same reply, it reflects about nine percent of the light. (Some people would describe that as being comparable to the reflectivity of asphalt.) That does not tell us anything about how heavy the material is, any more than black paint is heavier than white paint. But it surely does relate to the composition of the surface, and Dawn’s visible, infrared, neutron, and gamma ray spectrometers all will help determine what that composition is.

      You should not think of the surface of Ceres, however, as looking like it might have when it formed near the dawn of the solar system. (I wrote about Ceres, including its formation, in December.) That was more than 4.5 billion years ago. Many internal geological processes on the dwarf planet have taken place since then that have affected the surface. In addition, it has been exposed to the space environment and been subjected to impacts by asteroids, many of which are composed of dark materials.

      I do not want to take the time to delve into other missions here, but there was no surprise in the surface of the comet being dark. All cometary nuclei that spacecraft have visited are very dark (even darker than Ceres).

      Dawn will map Ceres from four orbital altitudes, and I described them last year in February, May, June and August. We will cover the entire surface quite thoroughly, including the bright spots. While they have understandably captured everyone’s attention right now, Ceres is a big place, and there is a great deal there to explore. We surely will make many more fascinating discoveries, and we want to learn as much about all aspects of this alien world as we can.

      Yes, there is an equivalent of a geostationary orbit at Ceres, but Dawn does not need to fly there, and we don’t want to miss the rest of Ceres! Indeed, there is no reason to stare at the spots, mesmerizing though they may be. The plans I described in those previous Dawn Journals ensure that we will make as many meaningful, productive measurements as possible of the spots and everywhere else. Just as at Vesta, we have formulated intricate plans that take the greatest advantage of our sensors to provide extensive coverage. I am highly confident that we will elucidate the nature of these spots without needing to make any significant changes to our plans.

      I’m glad you are following the mission. There is much more excitement ahead!


  16. Guillaume Vollant-Boulé says:

    Hello Dr. Rayman,
    Isthe isp and trust of the ion engines affected by the power (W) of the solar panels? So were they more powerful and efficient at Earth’s orbit?

    Thank you,
    Guillaume Vollant-Boulé

    • Romana Starfield says:

      The part of me that has an evil and warped sense of humour wants to say that the trust of the Dawn’s engine’s are greatest now that they have been proven for so long.
      However Marc mentioned in a past reply that yes, Dawn’s ion engines are more powerful when they receive more electricity from the solar panels which happened when it was closer to the sun.

    • Marc Rayman says:

      Hi Guillaume,

      For others, Isp (an abbreviation for a term that is no more helpful: specific impulse) is a measure of the efficiency of the ion propulsion system.

      Romana is right that the trust is very high now thanks to more than five years of accumulated thrusting :-) Excellent point!

      She is also correct that the thrust is lower now. I’ve written about this quite a few times, including, for example, in February and August 2010, when I described that as Dawn reached about twice Earth’s distance from the sun, we no longer had enough power to operate at the maximum thrust level, so we had to throttle down. (I also explained that we had accounted for this in the overall design of the mission.) I have long been fond of pointing out (including here) that it would take four days to accelerate from 0 to 60 mph (97 kilometers per hour). But in this Dawn Journal above, I claimed that it would take nearly 11 days. The difference is because the thrust is significantly lower now that Dawn is much farther from the sun. The basis upon which we chose the size of Dawn’s huge solar arrays was ensuring that the probe would still have enough electrical power even out here, at Ceres, to operate its ion engine and all of its other systems.

      Dawn’s ion engines can be operated at 112 throttle levels, each corresponding to a different power level and different thrust. Over that entire range, Dawn’s lowest thrust level is around 20 percent of its highest level.

      The specific impulse is a little bit more complicated, but, in brief, it does not change by as much as the thrust. Even over a broad range of throttle levels (i.e., over a broad range of power), the engine efficiency is mostly unaffected. At low throttle levels, it does decrease, but the lowest efficiency is a bit more than half of the highest. And in all cases, it is far above that of conventional chemical propulsion, which is what makes this ambitious mission possible.

      I hope this quick (albeit late) response is helpful.

      Thank you for being so interested (and thanks to Romana for being more concise and prompt than I am, though with no more of a warped sense of humor).


  17. Mike says:

    The last photos published were on Feb. 19, now more than 3 weeks ago (23 days). Must be a LOT of extraterrestrial bases and activity to digitally “scrub” from the photos NASA has gotten since then!!! Such a lengthy delay to publishing more photos, those bright spots aren’t just water ice accumulations, but ET artifacts. And so many, it may just take months to “scrub” those photos or maybe the whole mission will be scrubbed???

    • Marc Rayman says:

      Hi Mike,

      I’m sorry you have missed some of our great pictures! The last photos released were taken on March 1, and they are the latest ones taken by our distant explorer. They are the crescent views of Ceres in my Dawn Journal above. (I apologize if the caption is not clear.) In January and February, I presented tables showing the schedule for photography (along with an explanation for why we don’t take more pictures during this phase of the mission). We have released pictures from each observation. You can find them here in my Dawn Journals and in our image gallery. As I wrote, we will not take pictures again until next month, and I hope you will check back to see them as well.

      Thank you for your interest in this ambitious mission of adventure and scientific discovery!


      • I find that very hard to believe. It seems like this would be the time to take photos! Not a month from now. The newest photos posted are no better than the photos taken a month ago. I dont know for what reason, but my gut tells me NASA is playing cover up once again.

        • Marc Rayman says:


          I think it’s hard to believe because the situation is so counterintuitive. Let me explain a little more, although the more complete explanations are in my November, January, and February Dawn Journals. If you really are interested enough to understand the complex deep-space acrobatics, rereading them may make it clearer. I’ll offer a summary here…

          Dawn is aiming to reach its first mapping orbit next month at an altitude of 8,400 miles. To maneuver, we use the ion propulsion system, which I have described many times as very efficient, but very, very gentle. Even at maximum throttle, the ion engine pushes on the spacecraft no harder than a single piece of paper would push on your hand. Note in my Dawn Journal above, it would take Dawn almost 11 days just to change its speed by 60 mph (97 kilometers per hour). So it doesn’t use much propellant, but it requires patience. (I wrote more about the throttle level and the low thrust in the comment above.)

          Now, Dawn entered orbit on March 6, but the part of the orbit it is in now is over the night side of Ceres. We cannot photograph Ceres when it is such a thin crescent. Your intution may be influenced by thinking of Earth orbits, but Earth is much more massive. Ceres is far larger than asteroids but far smaller than Earth. Its gravity is not as strong, so orbits are slower. In fact, even when Dawn descends to 8,400 miles, one revolution will take more than 15 days. At higher altitude, the orbit is still slower, meaning long times are spent traveling above the night side of Ceres. (I have explained this in several Dawn Journals, including here. Consider that in low Earth orbit, like where the International Space Station is, it takes only 90 minutes to complete a revolution. The moon, which is much higher, takes four weeks to revolve around and travels at a much slower pace.) So Dawn can take many weeks to complete one loop around Ceres, spending a long time on the side that’s in the deep darkness of night. And that is where it is now.

          In fact, let me offer an amazing fact about Dawn’s orbital motion. Right now, as I write this, Dawn is more than 46,500 miles (75,000 kilometers) above its new home. From the spacecraft’s point of view, Ceres appears too close to the sun to photograph it, but how quickly is the situation changing? Relative to Ceres, Dawn is moving at the incredible speed — are you ready for this? — of 42 mph (68 kilometers per hour)! At this altitude, Ceres’ gravitation grip is weak, so even though Dawn is held in orbit, it moves slowly. That is what we achieved with the years of ion thrusting that preceded arriving in orbit: getting Dawn’s motion to (almost) match Ceres’ motion. And as the spacecraft heads for the apex of its orbit, the gentle thrust of its ion engine and Ceres’ gravity work together to slow it down even more. That is why we require patience before the spacecraft will reach the sunlit side of Ceres again. (Also note that the figures in November let you count Dawn’s progress day by day using the white circles. Remember when you look there that “capture” was on March 6.)

          Look again at the similar figure (and associated text) last month showing the long, gradual, graceful, looping trajectory that ends in the first mapping orbit on April 23. The sun is far off the left side of the figure, and right now Dawn is on the right side, opposite the sun from Ceres. Even when it entered orbit on March 6 (labeled as “Capture by Ceres’ gravity”) it was already over the side of Ceres in shadow. When it loops around to OpNav 6 on April 10, it will finally be able to see a thin crescent again, as I describe in the paragraph below the figure.

          Finally, you are quite right that the newest photos are not better than previous ones (at least from the standpoint of resolution — I happen to think the crescent is quite attractive). You can see from that same table last month that the latest photos (from OpNav 5) were taken from a greater distance than RC2. Dawn entered an elliptical orbit. I explained in February that it was at its closest to Ceres on Feb. 23, and its momentum has been carrying it to higher altitude since then, so the resolution of the latest pictures is not as good as some of the previous ones. The exquisitely gentle ion thrust is gradually slowing the spacecraft down, reshaping its orbit so that next month it will be in the desired circular orbit, but that is all happening over the night side. Hence, no pictures for a while!

          Difficult to grasp as this complicated story is, Dawn’s ongoing success is the result of exquisitely detailed planning of very intricate operations, and I apologize if the explanations in my Dawn Journals (and my associated comments) fail to convey clearly what is going on. But think of this: we are discussing how an interplanetary spaceship using advanced ion propulsion maneuvers in orbit around a distant dwarf planet, the first one ever visited. It sounds like science fiction, but it is science fact! Part of what is exciting is that no spacecraft has ever undertaken an expedition like this. We are all sharing in a unique adventure. I think that is really cool, and I hope you do too!


          • Andrew R Brown says:

            Hi Marc,

            Looks like a couple of youtube trolls have decided to peep their heads above the parapet. There is so much nonsense on there along with the Creationist hoax, Electric Universe hoax, Nibiru hoax, UFO hoaxes, etc.

            Too many unemployable single teenage boys living at their parents houses with not enough to do but populate Youtube with such nonsense. In future, it’s better to just delete such nonsense.

            Looking forward to RC3 by the way and will when find time to properly comment on the fantastic images we already have.

            Andrew R Brown. Ashford, Kent, United Kingdom.

            • Romana Starfield says:

              Andrew I agree wholeheartedly, except, I think some of these conspiricy theorists may actually be adults. Move along folks, nothing to see here that hasn’t already been seen till mid April.

              • Andrew R Brown says:

                Thank You Romana for your support.

                Conspiracy nuts drive me insane where there is none.

                The abuse of NASA and ESA material and imagery on You Tube and elsewhere is rampant, I have reported these abuses on several occasions now.

                This is a serious science blog, hopefully the conspiracy trolling can be kept out. :D

                Dr Marc Rayman and everyone else at JPL, NASA, JHU (MESSENGER and New Horizons two other missions I follow extremely closely on and comment on), APL, ESA etc are doing a fine job at helping to eradicate ignorance, but unfortunately, many people who are ignorant refuse to be helped. :(

                Andrew R Brown. Ashford, Kent, United Kingdom.

  18. Edward Quinn says:

    I wish to join the many who are congratulating you and the rest of the Dawn team for an inspiring scientific and engineering achievement. You have demonstrated that what seemed nearly impossible to obtain in terms of the desire for knowledge about the nature of the universe can be realized through years of dedicated hard work, and that the result can be very unexpected, exciting and suspenseful to witness as the story unfolds.
    I have followed along with Dawn from the launch, through its path to Vesta (it seemed to me like it would never escape Mars gravitational embrace), the discoveries there and now its journey to Ceres. Your narrative has provided me with with a ~ once a month glimpse into the drama of scientific discovery and a great engineering feat. Once again congratulations.

    • Marc Rayman says:

      Thank you for your very nice message, Edward! I greatly appreciate it, and I know the rest of the Dawn team does as well. I am delighted you have been with the mission all along, and it’s great to see that you have been so interested and engaged. I am happy you will continue to be sharing in our collective exhilaration of exploring an alien world.

      Thank you again.


  19. Alex R. says:

    Hi Marc,
    what findings do you think would it take to shift NASA interest from Europa to Ceres?

    Let me rephrase, of course it is hard to beat Europa on this front, but on the other hand Europa is much more difficult to reach than Ceres, not only financially and technologically but also in time (about twice as much).
    So if for example Dawn discovers that the bright spots are water ice and below it liquid ocean, will it be enough to change plans and send exploration probe to Ceres instead of Europa?

    • Marc Rayman says:

      Hi Alex,

      NASA follows a very deliberate process for deciding how to expend precious taxpayer funds to explore the solar system and beyond, and there are too many issues for me to explore in this forum. If others want to discuss it here, have fun! I will devote my limited time to responding to questions that I really can answer, rather than offering speculation that ultimately will prove to be of little value. It would be enjoyable, to be sure, but I regret I can’t afford it.

      In brief, however, there would be no reason to change the plans for Europa based on anything Dawn finds at Ceres. That moon of Jupiter is interesting in its own right, and with so much data on it already (thanks to extensive observations by previous NASA spacecraft), NASA can work on the next exciting mission right now. In fact, we already are! Europa is a very high priority for the planetary science community, and great progress is being made on devising a really cool mission devoted to it. It will take a while to digest Dawn’s findings at its new home, then to formulate compelling questions, and then to establish what follow-up mission would be appropriate. By then, I would hope we will be well on our way to realizing a mission to make more new discoveries at Europa.


  20. Ulf Holmström says:


    Congratulations on this giant leap in space exploration.

    Ive been following dawn since launch and im so looking forward to seeing some close up pictures.

    When will you share these?

    Best regards,
    Ulf, Sweden

    • Marc Rayman says:

      Thank you, Ulf. I’m pleased you’ve been along for this adventure for so long.

      We will share the close up pictures when we get them. Last month, I presented the schedule for photographing Ceres during this part of the mission, and we have released pictures from each of the photography sessions. We will continue to do so. During the course of the year, Dawn will operate in four mapping orbits, and I wrote about them in February, May, June and August. So, as we progress from one to another, the pictures will get better and better, and we will share them as they improve.

      You can always go here to see Dawn’s pictures of Ceres.

      I hope you continue to follow Dawn!


  21. Andrew BROOKS says:

    Hi Marc

    What intrigues me the most is the way those two bright white spots are still glowing bright as it revolves into night time side. Have a quick look at the video at the top of your 6th March Dawn Journal and you will see what I meant.

    Any explanations why it is still glowing on the dark side soon after sunset? Perhaps it will be a good idea to try take a photo of these ‘bright spots’ to see if it is still glowing at midnight Ceres time?

    Yeah! I am still enjoying that celestial ride!

    Andrew BROOKS (Sydney)

    • Marc Rayman says:

      Hi Andrew,

      We discussed this briefly below and in comments on previous Dawn Journals. It is hard to tell from this animation, but careful examination of the pictures we have already shows the spots do not continue to glow when they enter the shadow. They are reflecting sunlight, and when the sunlight no longer reaches them, they disappear.

      One of the many standard scientific techniques of investigating the nature of planetary surfaces is to measure how much light they reflect as both the illumination and viewing angles change. (I referred to this in another comment below.) The illumination angle means the angle between the sun and the surface. The viewing angle is the angle between the surface and the sensor (in this case, Dawn). Scientists have studied reflections theoretically as well as in laboratory experiments, and they have observed the reflections from many extraterrestrial bodies, both telescopically and with spacecraft. Thanks to Dawn’s approach trajectory, we already are getting a wealth of such data at Ceres. As we see in the animation above and last month’s table (as indicated in the next-to-last column) and diagram, Dawn views Ceres over a wide range of angles. In addition, as Ceres rotates while Dawn watches, the angle between the sun and any particular location on the surface (including our mysterious friends the bright spots) changes quite significantly even over the course of a few hours. (Similarly, for those of you on Earth, the angle of the sun changes by 90 degrees in the six hours from sunrise to noon. Ceres rotates 2.7 times faster.) The analysis has not yet revealed what the spots are, but this method will contribute to figuring it out.

      Of course, many other techniques will be applied to analyzing them as well, especially their appearance in the higher resolution pictures from our first mapping orbit in early May as well as the visible spectra and the infrared spectra.

      Intriguing as the spots are, I should point out to everyone that there are plenty of materials known in the solar system that are 40 percent reflective or more, as these spots are. One example that may interest everyone who follows Dawn is Vesta. Yes, the average surface of that giant protoplanet, which Dawn explored in 2011-2012, reflects that much light. There are other places in the solar system that reflect nearly 100 percent of the light. What makes the bright spots on Ceres mysterious is that they are so much brighter than the rest of Ceres. Most of Ceres reflects about nine percent of the light. So it is the contrast with their surroundings that makes them so peculiar.

      We have much to learn as the celestial ride continues. Thank you for being part of it.


  22. Kamal Lodaya says:

    Great to get into orbit. Are you at some future point in a position where a solar eclipse lets you get a peek at a possible atmosphere?

    • Marc Rayman says:

      Hi Kamal,

      Dawn is designed to operate in sunlight, and we keep it out of eclipse. The last time it was in the shadow of a planet was the day it left Earth. Nevertheless, as I have written in several comments in recent months, including below, Dawn will look for evidence of an extremely thin veil of water vapor above Ceres when it is on the night side in late April.


      • Guillaume Vollant-Boulé says:

        Hi Marc,
        In the animation of the arrival at Ceres, Dawn is shown to be in a polar orbit, witch croses the shadow of Ceres. As I understood by your comment, Dawn will not be in the shadow of Ceres, so is the depiction of the video false?

        Thank you,
        Guillaume Vollant-Boulé

        • Marc Rayman says:

          Hi Guillaume,

          As the animation shows, Dawn is maneuvering to change its current orbit into a circular, polar orbit. (As a reminder for others, that means that its orbit takes it over both poles, as explained here.) And you are quite right that Dawn will never enter the shadow of Ceres (nor did it enter Vesta’s shadow).

          The animation is correct. Note the parenthetical caveat I put in the caption: The size of Ceres is exaggerated compared to the size of the orbit here. So while it looks like Dawn would enter the shadow, it actually does not because the shadow is so small. Let’s take a more careful look at this.

          The animation concludes in the first mapping orbit (RC3) at 8,400 miles (13,500 kilometers) altitude. Ceres is about 600 miles (nearly 1,000 kilometers) across at the equator. So at that distance, Ceres doesn’t block a large part of Dawn’s view of the sky. (The first figure in February 2014 shows the orbit and Ceres to scale. Recall that the approach to RC3 has changed significantly since then, but RC3 itself has not.) From the spacecraft’s perspective, Ceres will be the same size as a soccer ball 10 feet (3 meters) away. So as long as Dawn doesn’t go exactly behind Ceres relative to the sun, it won’t be in shadow.

          To be more quantitative, the angle of Dawn’s orbit plane relative to the sun will be between 5 and 9 degrees during its time in RC3 orbit. To picture this, imagine one of the famous Dawn clocks described in many of my Dawn Journals. For convenience, let’s say the clock is horizontal. The clock is one foot (30 centimeters) in diameter, with Ceres, in the center, about 0.4 inches (one centimeter) across. The sun is far away but aligned with the 12. Dawn’s orbit is a circular loop the same diameter as the clock’s (what an amazing coincidence!), but the plane of the orbit is vertical. If the orbit went down through the 12, curved underneath the clock, came up through the 6, and then arced above before diving back down to the 12, Dawn would be in shadow when it was at the 6. But we are aiming for an orbit that goes down through the first tick after the 12, where the minute hand would point at one minute after the hour. Then after passing beneath the clock, the orbit would come up where the minute hand points at 31 minutes after the hour. That angle is too small to be evident in the video, but it’s enough to keep the spacecraft in sunlight constantly throughout an orbit.

          I wrote more about the alignment of orbits at Vesta relative to the sun here.

          I hope this quick (albeit wordy) explanation answers your question.


          • Leonard Cottrell says:

            In the animation, Ceres is shown rotating in a “lefthand” sense. That is in the direction of the fingers of your left hand
            if you make a fist with thumb pointing north, or up. this is opposite to most solar system rotation and revolution. it keeps puzzling me

            this project/mssion is beautiful in many many ways—great

            • Marc Rayman says:

              Hi Leonard,

              Ceres rotates in the opposite direction from what the animation depicts. The animator used some (inaccurate) artistic license in Ceres itself while focusing on Dawn’s trajectory, direction of the ion beam and angle to the sun with data used in flight operations. I apologize for that distracting error, but I’m glad you’re interested enough to pay careful attention to the mission!


  23. rafael says:

    Congratulations on your great work.
    Perhaps it would be useful to science, take a picture with a time of long-exposure from the dark side of ceres, to pursue detect the diffused light of any possible gas plume.
    Best regards

    • Marc Rayman says:

      Thank you, Rafael.

      I agree with you that it would be useful. I wrote about this below, explaining that Dawn will look for evidence of water vapor above Ceres using the camera and the visible and infrared mapping spectrometers.


  24. Kevin W. Smith says:

    Congratulations Dr. Rayman and all involved! This is so exciting and fascinating! I’ve been following the Dawn mission from the start, and so very happy now that it is in orbit at Ceres. How fun as well that New Horizons will buzz Pluto soon! What a year for Astronuts! Best wishes on the coming science, I will be watching with great interest!

    Kevin W. Smith

    • Marc Rayman says:

      Thank you very much, Kevin. It’s always good to hear from someone who has been along since the beginning. We’ve had a terrific adventure together, and I’m glad to know you will be here for the wondrous discoveries that lie ahead.


  25. Hi:

    I did a comparison between images obtained by the Herschel Telescope water vapor in Ceres and map done for you with the spacecraft Dawn, I believe, and match the peak emission of water twice bright spot of Ceres. Moreover, upon entering the shadow this region, it seems that this illuminating a peak of a mountain. They can be cryovolcanoes water? Thank you and congratulations.

    The comparison

    The region enter on shadow.

    • Andrew R Brown says:

      Hi Claudio,

      Yes the bright spot is certainly the central peak of a crater. In fact, the reason for it being so bright is certainly the central mountain has step sides, allowing for regular landslides to keep it ‘clean’ from space weathering.

      Also I suspect the other bright spot to the east in the same crater is a very recent landslide on the crater wall.

      Cryovolcanism is certainly not happening as 1 Ceres lacks both tidal heating and internal radioactive heating. The very tenuous vapour is just sublimation.

      Andrew R Brown.

  26. Gareth says:

    To all the Dawn team congratulations on a remarkable achievement of the first Nasa team in history to get a space probe orbiting two celestial bodies and using the remarkable ion propulsion system. The tortoise can really beat the rabbit to its destination without causing everyone to hold their collective breaths and fingers crossed.
    Hopefully your findings will not get lost in all the hype surrounding the arrival of New Horizons to Pluto just a few weeks after your close up pictures start coming through. A bit of a David and Goliath task in terms of the romance of it all.
    However if I were to suggest that the bright spots are a series of limestone coated pyramids in a specific configuration like our own used to be then I think Pluto findings might be overwhelmed by yours. Of course I know my suggestion would be fanciful and ludicrous in terms of having some sort of alien life form to build them and why there???…..but in technical terms of what you are seeing could they fit?

    I believe our pyramids when first built gave a 40% reflective rate due to the limestone coating on them and could be seen from space. I am sure you would agree that this explanation would capture the imagination of all humanity more than ice lakes, icy volcanoes or deposits of shiny metals. We must also remember that not that long ago the suggestion that the world was round, we will have flying machines, giant lizards walking the earth was laughed at but all eventually proved scientifically and yet so many who laughed at these believed a man could come back from the dead….a leap of faith. So for the next six weeks I will take that leap until you prove otherwise.

    • Marc Rayman says:

      Thank you for your nice message, Gareth. The tortoise and the hare is a good comparison.

      Space exploration is not a competition. I hope for exciting and productive outcomes of all missions and all scientific investigations. Yes, Pluto may overshadow Ceres, but that’s OK. Celebrity is not a measure of value, and I think there is enough romance for all missions. No mission’s success can possibly diminish another’s. Rather, ambitious, curious people like us are rewarded by all successes.

      Even here on the Dawn blog, many people treat Pluto as special because they grew up during that short period in human history when it was called nothing but a planet. They are not so aware that Ceres had a similar history, as I described in December.

      I got a nice chuckle from your pyramid joke. Thank you. For people who visit this site without already appreciating the context of our conducting thoughtful discussions based on the scientific process (or discussions for pure fun!), I wouldn’t want them to think we are serious about such silliness. So for you new readers, I would mention that Dawn is only able to conduct its exceptionally challenging and spectacularly successful cosmic journey because of the unfailing commitment of everyone on the team to rigorous and careful thought. Abandoning critical thinking at nearly the last step of this grand undertaking, when we start to analyze the amazing findings returned from our sophisticated robotic probe across the solar system, would be the ultimate insult to our collective intelligence and would amount to a rejection of the very principles that were required to get us this far. There is a basic principle in logic commonly expressed by Bertrand Russell’s teapot. (Look it up if you’re interested.) I like the way Christopher Hitchens succinctly summarized it: “What can be asserted without evidence can also be dismissed without evidence.”

      I know humor can lose its value when it is scrutinized, so I won’t do that, and I apologize for diverting from your fanciful remark to caution others not to misinterpret it.

      Thank you again for your fun message.


  27. John Calvert says:

    One glaring question – why does the GIF image not actually show a full rotation? The first frame in the GIF movie is the one with the bright spot in the center. The frame prior to that (i.e. last in the GIF) shows no bright spot at all – in fact no relation to the first frame. This is easily seen by loading the GIF into PhotoShop and looking at the layers (each frame is a layer). There are 27 frames in the GIF.

    The next observation I have: When the bright spot is shown in the shadows on the right edge, in frames 4 and 5, it is still very bright, as it was in the first frame. Logically it seems this can mean only one of two things: 1) light is being emitted from the center of the crater (not reflected), or 2) something is standing very high, above the rim of the crater, which is very reflective of sunlight. Either possibility is very interesting. Looking at frames 4 and 5, the faintness of the second bright spot (to the right of the brighter one) supports the idea that light is being emitted from the center of the crater. In this case, the second bright spot is a reflection off the crater wall of the very bright light being emitted from the center of the crater.

    • Marc Rayman says:

      Yes, John, you are quite right that the animation is not complete. As I wrote below, when the science team has time to make a better animation from the RC2 images, we will be happy to release it. This was just a quick version.


  28. Andrew R Brown says:

    Congratulations Marc and to all at the DAWN team for the successgful orbital insertion at 1 Ceres.

    Whilst there is a five week wait till the next data collection including images, there is much to talk about with the RC 2, OpNav 4 and OpNav 5 images.

    The crescent 1 Ceres images are captivating as are the RC 2 images.

    1 Ceres certainly is like a cross breed between the Saturn moons Rhea and Tethys and the Uranus moons Umbriel and Oberon.

    The southern hemisphere grooves are different and interesting, wonder if they are graben (extensional faulting of the crust) or are crater chains?

    Andrew R Brown. Ashford, Kent, United Kingdom,

  29. Romana Starfield says:

    Wow, I was hoping for another blog entry and this one is another well written and witty one. Thank you heaps for keeping us informed, keeping us entertained and all of the wonderful hard work (and dancing) you have put into this mission. Thanks also to the rest of the Dawn team.
    I loved the breakfast with Ceres video. I was just in the supermarket today and realised that yes cereal is derived from Ceres, the Roman god of agriculture and grain. Until that was pointed out, I didn’t make the connection.
    Looking at the animation, I see that sunlight is coming from the left of screen. The two bright spots light up as they are about half way across the face or Ceres. I suspect what we are seeing is sunlight reflecting off of the slopes of a central peak and the side of that crater. Kind of on an angle. So as Ceres rotates, different parts of the peak and slope reflect sunlight towards Dawn. This could explain why they appear to shine as the rest of Ceres gets dark. I expect that as Dawn takes up orbit that we shall see that depending on the angle of the Sun and the position of Ceres, the two shiny spots may appear on the left side of the crater rather than the right side. I have not worded this terribly well, but basically you get the picture.
    Now I know the naming convention on ground features will be based on the gods of agriculture, however it would be rather nice to set one aside as the Nimoy Crater, in honour of one who recently passed away, but who lived long and prospered.
    So, April will be when the next photos are available. You know that’s perfectly timed for some great announcements about the nature of the bright spots on April 1st. On April 10th I shall be preparing for a journey back to Australia from Thailand. Just in time to see the newest pictures of Ceres. I like how you have scheduled these events around my holidays.
    Once again, no reply needed. Just putting down my thoughts.

    • Marc Rayman says:

      I always appreciate your kind comments, Romana, as well as your thoughtful concern for my time!

      Your interesting analysis is based on the bright spots lighting up when they’re halfway across Ceres in the animation at the top of this page. Unfortunately, that’s an artifact of the way the animation was made. If you look carefully, you’ll see that the animation has a jump in it when it repeats. The bright spots show up in the middle of Ceres because that’s where the animation starts, not because that’s where they first reflect light. When the folks who make attractive products for public release have more time, we will have a video that more clearly shows the spots being visible essentially the whole time that crater is in sunlight. Nevertheless, I understand what you are describing, and part of the effort to understand their nature is to quantify how bright they appear to be at different angles.

      Leonard Nimoy’s portrayal of Mr. Spock still means a great deal to many of us, but I don’t believe it is likely there will be an exception to the plan for naming features on Ceres. But I would think you would be happy the convention is based on Piazzi’s decision to name Ceres after a Roman goddess, Romana.


  30. Sean Deany says:

    Good work Marc. Its been a thrilling ride and things are just going to get better when it comes to new discoveries Dawn will be making. There must have been some sigh of relief for the Dawn team once orbital proceedure was made.

    I look forward to possible finds of a teneous atmosphere at Ceres. Will this be possible during the April observations and for finding a moon(s) would be a huge thrill for us all.

    On 6th March as said in previous comments I made it to Ceres – the little town located outside of the Victorian city of Geelong in celebration to the approach made that same day by Dawn to the real Ceres. Looking up into the sky and in the southern hemisphere about 30 degrees ahead of the Sun I beleive I saw an ever so tiny spec glimmering for a moment!

    Ceres now has a moon and its called Dawn.

    • Marc Rayman says:

      Thank you, Sean.

      We are indeed going to search for signs of water vapor above Ceres at the end of April. I wrote a little about this here. As a reminder, however, this is going to be a very challenging measurement. I’ve tried to point out there and in several comments in subsequent months that Dawn’s instruments were designed to probe the surface and subsurface of alien worlds without atmospheres. The detection of water vapor was reported more than six years after Dawn left Earth, so we will do the best with the sensors we have.

      I’m glad your journey to Ceres was successful. There must have been some sigh of relief once you made it there. Ceres now has had a visitor and his name is Sean.


  31. Congratulations! It has been a long wait.

    I noticed you decided on “Cerean” for the adjective instead of “Cererean” or “Cererian.” Since whatever you guys use is apt to become the standard in the future, I don’t blame you for wanting it to be simple, but I’m a little sad to see that the Queen of the Asteroids didn’t get an exotic adjective like her neighbors Mars (Martian) and Jupiter (Jovian) have.

    • Marc Rayman says:

      Thank you, Greg. Yes, 214 years is indeed a long wait ;-)

      You and I discussed the adjectival forms of Vesta and Ceres five years and 1.9 billion miles (3.0 billion kilometers) ago, when those two worlds were still no more than tiny smudges of light and Dawn had four healthy reaction wheels. I liked your reasoned recommendations. In my Dawn Journals through arrival at Vesta, I decided to use “Vestian” based on your linguistic analysis. In 2011, the Dawn principal investigator decided that it should be “Vestan,” so I adopted that word the next month. At the same time, he determined that we would use “Cerean.”

      What these places lack in exotic adjectives, they more than make up for in exotic geology and pure coolness!


      • In that case, I’m just grateful he didn’t decide on “Vestal” and “Cereal.” :-)

        Best of luck with the mission at Ceres. It looks like you have something more interesting than anyone had anticipated.


  32. Fabian P. says:

    What an achievement!

    I loved reading this year’s (humorously written) blog entries and how they shed light on Dawn’s mission.

    Can’t wait to see what secrets Dawn will unveil in the future. This year is going to be exciting.

  33. kurt/PL says:

    Hi, I wake up early in the morning to see new picture of spots but here are still the, when we will see picture of today 6.3.15 with of course better quality and zoom of mistery spots? I think that people waiting for that like never before.

    • Marc Rayman says:

      Hi Kurt,

      In January and February I presented the details of the schedule for photographing Ceres, and I summarized it in this table. As you can see, we will not take photos again until April 10, and that will be of a narrow crescent. By the end of April, we will be returning more detailed pictures of the well-illuminated surface. In the meantime, Dawn is flying high above the night side of Ceres.


  34. Matt Gibbons says:

    A moment of silence for this moment of success.

    AND NOW IT’S TIME FOR A HAPPY DANCE (think of Snoopy from Peanuts cartoons)!!!!

    Congratulations to the entire team, but especially you Marc for your patience and class. Great job! So much more to come. This is gonna be amazing!


  35. Dear Dr. Marc D. Rayman and staff!

    Congratulations on driving more this important spacecraft’s mission Dawn in the first dwarf planet (1) Ceres.

    We are monitoring these fantastic results achieved so far.


    Antônio Campos
    Astronomy Groups
    CEAMIG – REA/Brazil and AWB

  36. Luis says:


    Interesting that many of the impact craters on the surface of Ceres show what look like to be central peaks uplift, even in some of the smaller size ones. How important will this type of complex craters be to understand the subsurface characteristics of the dwarf planet, namely its upper crustal composition?

    • OmCheeto says:

      I concur. I count at least 30 of these central peak objects. My guess is that the asteroids that created the craters, melted the ice, which must be very, very near the surface, and the water froze, before it could flow back. The “two headlights” peaks are possibly the newest, and haven’t had time to accumulate any cover dust. Just a theory, of course. :)

    • Marc Rayman says:

      As you so correctly imply, Luis, the detailed structure and shape of craters of different sizes will provide scientists with very important clues about the strength and hence composition of the crust. For others, I wrote about a slightly different aspect of this here, which may help illustrate how the properties of the crust affect the appearance of the craters.


  37. Jeff K says:

    I would also like to congratulate the Dawn team. I’ve been following this mission ever since Vesta and I love Marc’s blog and its level of detail (and its style!). Thank you, Marc, for putting the effort into writing it- there really are lots of us out in the public who hunger for this info. Can’t wait to see what those bright spots are!


    • Marc Rayman says:

      Thank you so much, Jeff.

      My comments immediately below apply just as well here. Having felt that same hunger myself for information about space missions, I have been very happy to be able to inform others. (I wrote more about this here.) Thank you for confirming that the effort is worthwhile.

      We are all fascinated by the bright spots. And I am confident that even after we explain that captivating mystery, there will be many more fascinating discoveries at Ceres we can’t even anticipate now. We’re going to have a great time here, and I’m glad to know you’re along for the adventure.


  38. Guillaume Vollant-Boulé says:

    The Dawn team ROCKS!!! You should be proud.

    Quick as always Dr. Rayman, although you write them in your spare time, the effort is worthwhile and you are connecting with the public. This is really important in or time of fast communication. I think that makes you the best speaker of the Dawn mission or of any robotic mission at NASA right now and even in the whole world, I should say.

    Thank you again,
    Guillaume Vollant-Boulé

    • Marc Rayman says:

      I greatly appreciate your very generous comment, Guillaume. Did my mom tell you to write that? :-)

      I know from so many of my own experiences as a lifelong space enthusiast how much the outside world wants the inside view. Although I have trouble finding the time for it, all I’m really doing is telling everyone how cool all this is from my standpoint. I am very happy it is well received.

      I could not agree with you more about the Dawn team. I may be a more active spokesperson, but the success of this extraordinary expedition is the result of the combined efforts of a team of dedicated and diligent men and women.

      So both for myself and on their behalf, thank you!


  39. Alan Mintaka says:


    How was the arrival date of March 6 determined? The first video shows the thrusters firing constantly from about the third week in February until April 24/25, when the probe actually enters orbit around Ceres. Was the arrival date determined to be the time the probe “turned around” to start approaching Ceres prior to actually orbiting it?

    If those thrusters fail at any time between now, March 6, and April 24/25, will the probe still “remain in residence at the alien world”?

    Thanks for your time,
    Alan Mintaka

    • Marc Rayman says:

      Hi Alan,

      Arrival is defined to be when Dawn enters orbit, and that was this morning (March 6). The ion engine is continuing to fire because we are reshaping the orbit. The video shows the engine going off on April 23 when we have achieved the shape we want for our observations. After a bit more than two weeks in that orbit, we will reshape it some more, spiraling down to the next observation orbit. I explained that maneuvering here.

      Dawn is in orbit in every sense, so, yes, as I wrote in the journal above, if it stopped thrusting, it would indeed remain at Ceres.


      • Alan Mintaka says:

        Thanks Marc. Obviously I’m a little out of my depth when it comes to celestial mechanics. I never fail to be amazed by how accurately these probes can be aimed over such long distances, and with so many forces involved.

        And in a few months New Horizons will be arriving at Pluto. Pluto! I never imagined that I’d see that in my lifetime.

        The first book I ever checked out of a library was The Golden Book of Astronomy, by Rose Wyler and Gerald Ames (introduction by Bart J. Bok), Simon & Schuster, New York, 1955. For me it was circa 1957, when I had just learned to read. Once I got into rare book collecting in my old age, I hunted down the same edition and bought it.

        What a thrilling ride it’s been. Thanks, Marc, for adding a very important event to it. Now, just what are those bright lights in that crater??? My guess is an active outflow of water vapor, with ice around the edges.

        Alan Mintaka

  40. David Brinza says:

    Congrats to you, the Dawn team and the awesome ion propulsion system that made the amazing journey possible!

    My wife (Dawn) and I have followed the mission closely since it launched on her “39th” birthday in 2007.

    Have a great tour at Ceres and send us a bunch of pictures!

    • Marc Rayman says:

      Thank you very much, David!

      I still have many fond memories of our work together on Deep Space 1 and its ion propulsion system. I’m glad you and your wife are following as Dawn builds upon that’s success. (I’m also glad she shares a name with this mission and not with the one we worked on together.)


  41. Charles A. Gardner says:

    The “lights” only stay “on” as long as the sun shines on them. In the last frame that they are still visible, the night side of the crater rim is also still lit by sunlight. In the next frame, the crater should still be in-frame on the dark side, but there are no lights. So, clearly, there are two somethings in that crater that are tall and highly reflective. But no artificial lights. My sources tell me that the whale-like creatures who inhabit Ceres’ ocean expel their garbage through the volcanic vent in the center of the crater… through an airlock on the roof of their world. They have no idea of the outside world of course. The trash freezes immediately in the cold of space, encased in a thin frozen shell of water that came with it. In Ceres’ light gravity, these ice-garbage balls soar up in a predictable arc and land several kilometers spinward (hence the second “light” which is actually sunlight reflecting off a huge pile of refuse (broken furniture and tools, inedible bits of Cerean prey animals, and out-dated used clothing). Apparently, these aliens may be more fastidious than we are. They keep their ocean clean.

    • Robin Miller says:

      The reflections are not from an alien city; they’re the lights of Ceres Central (L. Neil Smith’s “The Probability Broach” and “The Venus Belt”)!

  42. Chris Haines says:

    Thanks very much Marc for your always interesting blog. You have a knack for going deep enough to uncover the beauty of this space adventure the world is sharing and describing it in a way that can be appreciated by a wide audience from laymen to pros.

    One of the most captivating things for me has been watching the visuals of Dawn’s trajectory and the incredible route is has taken from launch through all the gravitational assists, Vesta entry/departure, cruise to Ceres and the current arrival. The Ceres capture is interesting in how the approach reminds me of a modern catapult roller coaster that shoots up the first hill and makes it to the hairpin turn at the top with just enough speed to hook over and head vertically down again. Another cool thing is how Dawn transitions from what looks like an equatorial orbit on approach to a polar orbit after capture.

    Regarding ion propulsion, what are some of the practical limitations of current technology? Ceres and Vesta have weak gravitational fields compared to many of the solar system’s larger moons. Are thrust to mass ratios of current ion technology suitable to support missions to larger moons in a practical time frame? In other words could missions to larger bodies be completed in 10 to 15 years or so from launch through arrival and science collection or would these missions require many decades to carry out? Obviously money, priorities and available launch vehicles have a lot to do with this but I’m thinking that we’re getting to the point where launch vehicles will be able to heft a massive amount of weight out of earth orbit.

    Thanks again for the great blog…

    Chris Haines

    • Marc Rayman says:

      Thank you for your nice comment, Chris. I really appreciate it.

      You are quite right that Dawn transitions from a near equatorial orbit to polar. I wrote about that here, but you can really see it in the video above. We take great advantage of the maneuverability provided by ion propulsion to optimize our orbits to get the best science we can.

      I am not specifically an ion propulsion advocate but rather an advocate of learning about the cosmos. The limitations and applications of ion propulsion are too involved to get into here, but I’ll offer a brief observation. I think of ion propulsion as a tool in the toolbox of mission designers. For some missions, it is essential. For others, it is not worth the cost or complexity. But certainly missions could go to larger bodies. We go to Vesta and Ceres because they are so interesting and, until Dawn, completely unexplored. But there have been studies of using ion propulsion to orbit the moons of Jupiter and many other destinations. One of the big challenges, however, is providing enough power. I wrote more about that here and in the comment that it links to.

      Launch vehicles will remain a significant consideration for a long time. They represent a large fraction of the cost of a mission. I’ve written that a mission to Vesta and Ceres would be truly impossible without ion propulsion. But even a mission using conventional propulsion to orbit only Vesta (the easier of the two to reach) would have been unaffordable within NASA’s Discovery Program of low cost/high return planetary missions. Part of the reason is that it would have required a much larger (i.e., more expensive) rocket. Dawn used a lower cost rocket and gets two worlds for the price of one mission.

      Thank you again!


  43. Larry says:

    So I see from the gif image, the “lights” still shine even when the crater is in shadow. How does that happen?

    • John Turner says:

      Maybe the spot is intensely retroreflective, like the material Caltrans makes road signs out of, and it is picking up and shining back at Dawn the light of its own ion engine.

    • Marc Rayman says:

      It may look like that, Larry, but that’s not actually what happens. You won’t be surprised to know that the pictures have been studied in detail, and the bright spots especially so. They really do disappear when they are no longer illuminated by the sun. I think what you see is just an artifact of the way the images are processed and strung together to make the animation.

  44. Congratulations on this outstanding achievement! We can’t wait to see what Dawn discovers.

  45. Nat says:

    Congratulations! It’s been exciting following your progress.

    “…its orbital acrobatics first will take it up to an altitude…”

    I contend that this should say “astrobatics” :-)

  46. keith says:

    Dawn has grasped the delicate bonds of ceres,
    And will dance the skies on laughter-siliconed wings; …

    John Gillespie Magee, Jr. I ain’t :)

    • Marc Rayman says:

      Thank you, Keith.

      And that’s OK. Keith John Gillespie Magee, Jr. ain’t! (Normally I explain references for others, but I’ll leave it for interested readers to do their own research here.)


      P.S. Dawn’s solar cells are not silicon. They are indium gallium phosphide, indium gallium arsenide and germanium. Try squeezing that in!

  47. Lewis Mammel says:

    “While there are countless questions about Ceres …”

    Foremost among them in my mind as an avid follower of the DAWN mission is, “What is the mass of Ceres?” Weren’t you going to tell us?

    The reason I’m interested is that I have been calculating DAWN’s orbital energy from data on the Where is DAWN now? graphic ( just to follow along,) and the mass of Ceres is the source of the greatest uncertainty, along with the +/- 1 mph velocity spec.

    Also, there is a value of 895.8E18 kg featured by featured by Google Search, which seems to be old, and I can’t imagine how such precision could have been obtained previously to DAWN’s arrival. In fact the Wikipedia value of (9.43±0.07)×10^20 kg is in better accord with today’s “arrival” milestone which is indicated by attainment of ZERO orbital energy, in first approximation of course.

    THANK YOU !!!

    • Marc Rayman says:

      Hi Lewis,

      I’m sure everyone has their own questions.

      I’ll give you a little insight into my harried writing: Shortly before I posted it, I deleted this from the end of my second paragraph. “(In May, we will provide an update to the exact time of orbit entry based on revised measurements of Ceres’ mass.)” I took it out only because I didn’t think most readers would care that much, especially that early in the article. I didn’t know you were reading! And now I can expect that you will be reading again in May :-)

      Your question is a little technical for me to delve into here without some lengthy explanations for others. In brief, however, you are right that not enough was known about Ceres to specify the mass as accurately as the number you found with Google.

      Thank you for your detailed interest!


  48. Luis says: