Marc Rayman
Marc Rayman
Chief Engineer/ Mission Director, JPL
Dawn Journal | March 31

by Marc Rayman


Dear Dawnticipating Explorers,

Now orbiting high over the night side of a dwarf planet far from Earth, Dawn arrived at its new permanent residence on March 6. Ceres welcomed the newcomer from Earth with a gentle but firm gravitational embrace. The goddess of agriculture will never release her companion. Indeed, Dawn will only get closer from now on. With the ace flying skills it has demonstrated many times on this ambitious deep-space trek, the interplanetary spaceship is using its ion propulsion system to maneuver into a circular orbit 8,400 miles (13,500 kilometers) above the cratered landscape of ice and rock. Once there, it will commence its first set of intensive observations of the alien world it has traveled for so long and so far to reach.

For now, however, Dawn is not taking pictures. Even after it entered orbit, its momentum carried it to a higher altitude, from which it is now descending. From March 2 to April 9, so much of the ground beneath it is cloaked in darkness that the spacecraft is not even peering at it. Instead, it is steadfastly looking ahead to the rewards of the view it will have when its long, leisurely, elliptical orbit loops far enough around to glimpse the sunlit surface again.

OP NAV 5 image

Dawn took this picture of Ceres on Feb. 19 at a distance of 28,000 miles (46,000 kilometers). Despite extensive speculation (see, for example, here), the nature of the bright spots is not yet known, but we can look forward to more detailed pictures and other data that will elucidate this mystery. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

Among the many sights we eagerly anticipate are those captivating bright spots. Hinted at more than a decade ago by Hubble Space Telescope, Dawn started to bring them into sharper focus after an extraordinary journey of more than seven years and three billion miles (nearly five billion kilometers). Although the spots are reflections of sunlight, they seem almost to radiate from Ceres as cosmic beacons, drawing us forth, spellbound. Like interplanetary lighthouses, their brilliant glow illuminates the way for a bold ship from Earth sailing on the celestial seas to a mysterious, uncharted port. The entrancing lights fire our imagination and remind us of the irresistible lure of exploration and the powerful anticipation of an adventure into the unknown.

As we describe below, Dawn’s extensive photographic coverage of the sunlit terrain in early May will include these bright spots. They will not be in view, however, when Dawn spies the thin crescent of Ceres in its next optical navigation session, scheduled for April 10 (as always, all dates here are in the Pacific time zone).

As the table here shows, on April 14 (and extending into April 15), Dawn will obtain its last navigational fix before it finishes maneuvering. Should we look forward to catching sight of the bright spots then? In truth, we do not yet know. The spots surely will be there, but the uncertainty is exactly where “there” is. We still have much to learn about a dwarf planet that, until recently, was little more than a fuzzy patch of light among the glowing jewels of the night sky. (For example, only last month did we determine where Ceres’ north and south poles point.) Astronomers had clocked the length of its day, the time it takes to turn once on its axis, at a few minutes more than nine hours. But the last time the spots were in view of Dawn’s camera was on Feb. 19. From then until April 14, while Earth rotates more than 54 times (at 24 hours per turn), Ceres will rotate more than 140 times, which provides plenty of time for a small discrepancy in the exact rate to build up. To illustrate this, if our knowledge of the length of a Cerean day were off by one minute (or less than 0.2 percent), that would translate into more than a quarter of a turn during this period, drastically shifting the location of the spots from Dawn’s point of view. So we are not certain exactly what range of longitudes will be within view in the scheduled OpNav 7 window. Regardless, the pictures will serve their intended purpose of helping navigators establish the probe’s location in relation to its gravitational captor.

Dawn’s gradual, graceful arc down to its first mapping orbit will take the craft from the night side to the day side over the north pole, and then it will travel south. It will conclude its powered flight over the sunlit terrain at about 60 degrees south latitude. The spacecraft will finish reshaping its orbit on April 23, and when it stops its ion engine on that date, it will be in its new circular orbit, designated RC3. (We will return to the confusing names of the different orbits at Ceres below.) Then it will coast, just as the moon coasts in orbit around Earth and Earth coasts around the sun. It will take Dawn just over 15 days to complete one revolution around Ceres at this height. We had a preview of RC3 last year, and now we can take an updated look at the plans.

Dawn's final swoop down to to RC3 orbit.

Dawn’s final swoop down to RC3 orbit. The sun is off the figure far to the left, and Ceres’ north pole points up. The farther Dawn is to the right side of Ceres here, the smaller a crescent it sees, because the illumination is from the left. The white circles are at one-day intervals. The trajectory is solid where Dawn is thrusting with its ion engine, which is most of the time. The labels show four optical navigation sessions, where it pauses to turn, point at Ceres, conduct the indicated observation, turn to point its main antenna to Earth, transmit its findings, turn back to the orientation needed for thrusting, and then restart the ion engine. Dawn was captured into orbit on March 6. Note the periods on the right side of the figure between OpNav 5 (on March 1) and OpNav 6 (on April 10) when Dawn pauses thrusting for telecommunications and radio navigation but does not take pictures because it would have to point its instruments too close to the sun. Apodemeter is the Dawn team’s word for the highest altitude in orbit, in analogy with the more common term apogee, which applies for Earth orbits. (Demeter is the Greek counterpart of the Roman goddess Ceres.) Dawn was at its apodemeter of 46,800 miles (75,400 kilometers) on March 18. For more on Dawn’s approach trajectory, see the overall description and figures from other perspectives in November (including the motion into and out of this flat depiction), further details (including the OpNavs) in February and an animation in March. Credit: NASA/JPL

The dwarf planet is around 590 miles (950 kilometers) in diameter (like Earth and other planets, however, it is slightly wider at the equator than from pole to pole). At the spacecraft’s orbital altitude, it will appear to be the same size as a soccer ball seen from 10 feet (3 meters) away. Part of the basis upon which mission planners chose this distance for the first mapping campaign is that the visible disc of Ceres will just fit in the camera’s field of view. All the pictures taken at lower altitudes will cover a smaller area (but will be correspondingly more detailed). The photos from RC3 will be 3.4 times sharper than those in RC2.

There will be work to do before photography begins however. The first order of business after concluding ion thrusting will be for the flight team to perform a quick navigational update (this time, using only the radio signal) and transmit any refinements (if necessary) in Dawn’s orbital parameters, so it always has an accurate knowledge of where it is. (These will not be adjustments to the orbit but rather a precise mathematical description of the orbit it achieved.) Controllers will also reconfigure the spacecraft for its intensive observations, which will commence on April 24 as it passes over the south pole and to the night side again.

As at Vesta, even though half of each circular orbit will be over the night side of Ceres, the spacecraft itself will never enter the shadows. The operations team has carefully designed the orbits so that at Dawn’s altitude, it remains illuminated by the sun, even when the land below is not.

It may seem surprising (or even be surprising) that Dawn will conduct measurements when the ground directly beneath it is hidden in the deep darkness of night. To add to the surprise, these observations were not even envisioned when Dawn’s mission was designed, and it did not perform comparable measurements during its extensive exploration of Vesta in 2011-2012.

This artist's concept shows NASA's Dawn spacecraft arriving at the dwarf planet Ceres (lower right). Dawn travels through space using a technology called ion propulsion, in which ions are accelerated out of an engine, giving the spacecraft thrust. The xenon ions glow with blue light.

This artist’s concept shows Dawn thrusting with its center ion engine high above the night side of Ceres, which displays only a narrow crescent below the spacecraft. The gentle but efficient thrust allows Dawn to change the shape of its orbit. It will complete this first phase of orbital maneuvering on April 23 when it achieves RC3 orbit. Credit: NASA/JPL

The measurements on the night side will serve several purposes. One of the many sophisticated techniques scientists use to elucidate the nature of planetary surfaces is to measure how much light they reflect at different angles. Over the course of the next year, Dawn will acquire tens of thousands of pictures from the day side of Ceres, when, in essence, the sun is behind the camera. When it is over the night side in RC3, carefully designed observations of the lit terrain (with the sun somewhat in front of the camera, although still at a safe angle) will significantly extend the range of angles.

In December, we described the fascinating discovery of an extremely diffuse veil of water vapor around Ceres. How the water makes its way from the dwarf planet high into space is not known. The Dawn team has devised a plan to investigate this further, even though the tiny amount of vapor was sighted long after the explorer left Earth equipped with sensors designed to study worlds without atmospheres.

It is worth emphasizing that the water vapor is exceedingly tenuous. Indeed, it is much less dense than Earth’s atmosphere at altitudes above the International Space Station, which orbits in what most people consider to be the vacuum of space. Our hero will not need to deploy its umbrella. Even comets, which are miniscule in comparison with Ceres, liberate significantly more water.

There may not even be any water vapor at all now because Ceres is farther from the sun than when the Herschel Space Observatory saw it, but if there is, detecting it will be very challenging. The best method to glimpse it is to look for its subtle effects on light passing through it. Although Dawn cannot gaze directly at the sun, it can look above the lit horizon from the night side, searching intently for faint signs of sunlight scattered by sparse water molecules (or perhaps dust lofted into space with them).

For three days in RC3 after passing over the south pole, the probe will take many pictures and visible and infrared spectra as it watches the slowly shrinking illuminated crescent and the space over it. When the spacecraft has flown to about 29 degrees south latitude over the night side, it will no longer be safe to aim its sensitive instruments in that direction, because they would be too close to the sun. With its memory full of data, Dawn will turn to point its main antenna toward distant Earth. It will take almost two days to radio its findings to NASA’s Deep Space Network. Meanwhile, the spacecraft will continue northward, gliding silently high over the dark surface.

On April 28, it will rotate again to aim its sensors at Ceres and the space above it, resuming measurements when it is about 21 degrees north of the equator and continuing almost to the north pole on May 1. By the time it turns once again to beam its data to Earth, it will have completed a wealth of measurements not even considered when the mission was being designed.

Loyal readers will recall that Dawn has lost two of its four reaction wheels, gyroscope-like devices it uses to turn and to stabilize itself. Although such a loss could be grave for some missions, the operations team overcame this very serious challenge. They now have detailed plans to accomplish all of the original Ceres objectives regardless of the condition of the reaction wheels, even the two that have not failed (yet). It is quite a testament to their creativity and resourcefulness that despite the tight constraints of flying the spacecraft differently, the team has been able to add bonus objectives to the mission.

Some might see a pancake, and others a sand dollar, in this new image from NASA's Dawn mission. Astronomers are puzzling over a mysterious large circular feature located south of the equator and slightly to the right of center in this view.

Dawn had this view of Ceres on Feb. 19 at a distance of 28,000 miles (46,000 kilometers). Among the puzzling features is the large structure below and to the right of center. Pictures in RC3 will be more than three times sharper. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

Dawn will finish transmitting its data after its orbit takes it over the north pole and to the day side of Ceres again. For three periods during its gradual flight of more than a week over the illuminated landscape, it will take pictures (in visible and near-infrared wavelengths) and spectra. Each time, it will look down from space for a full Cerean day, watching for more than nine hours as the dwarf planet pirouettes, as if showing off to her new admirer. As the exotic features parade by, Dawn will faithfully record the sites.

It is important to set the camera exposures carefully. Most of the surface reflects nine percent of the sunlight. (For comparison, the moon reflects 12 percent on average, although as many Earthlings have noticed, there is some variation from place to place. Mars reflects 17 percent, and Vesta reflects 42 percent. Many photos seem to show that your correspondent’s forehead reflects about 100 percent.) But there are some small areas that are significantly more reflective, including the two most famous bright spots. Each spot occupies only one pixel (2.7 miles, or 4.3 kilometers across) in the best pictures so far. If each bright area on the ground is the size of a pixel, then they reflect around 40 percent of the light, providing the stark contrast with the much darker surroundings. When Dawn’s pictures show more detail, it could be that they will turn out to be even smaller and even more reflective than they have appeared so far. In RC3, each pixel will cover 0.8 miles (1.3 kilometers). To ensure the best photographic results, controllers are modifying the elaborate instructions for the camera to take pictures of the entire surface with a wider range of exposures than previously planned, providing high confidence that all dark and all bright areas will be revealed clearly.

Dawn will observe Ceres as it flies from 45 degrees to 35 degrees north latitude on May 3-4. Of course, the camera’s view will extend well north and south of the point immediately below it. (Imagine looking at a globe. Even though you are directly over one point, you can see a larger area.) The territory it will inspect will include those intriguing bright spots. The explorer will report back to Earth on May 4-5. It will perform the same observations between 5 degrees north and 5 degrees south on May 5-6 and transmit those findings on May 6-7. To complete its first global map, it will make another full set of measurements for a Cerean day as it glides between 35 degrees and 45 degrees south on May 7.

By the time it has transmitted its final measurements on May 8, the bounty from RC3 may be more than 2,500 pictures and two million spectra. Mission controllers recognize that glitches are always possible, especially in such complex activities, and they take that into account in their plans. Even if some of the scheduled pictures or spectra are not acquired, RC3 should provide an excellent new perspective on the alien world, displaying details three times smaller than what we have discerned so far.

Dawn activated its gamma ray spectrometer and neutron spectrometer on March 12, but it will not detect radiation from Ceres at this high altitude. For now, it is measuring space radiation to provide context for later measurements. Perhaps it will sense some neutrons in the third mapping orbit this summer, but its primary work to determine the atomic constituents of the material within about a yard (meter) of the surface will be in the lowest altitude orbit at the end of the year.


Dawn’s four mapping orbits, shown to scale in altitude with the size of Ceres, which is about 590 miles (950 kilometers) in diameter. (Note: colors of the orbits here are only approximate.) The table below includes links to descriptions of the activities in each orbit. Credit: NASA/JPL

Dawn will conduct its studies from three lower orbital altitudes after RC3, taking advantage of the tremendous maneuverability provided by ion propulsion to spiral from one to another. We presented previews last year of each phase, and as each approaches, we will give still more up-to-date details, but now that Dawn is in orbit, let’s summarize them here. Of course, with complicated operations in the forbidding depths of space, there are always possibilities for changes, especially in the schedule. The team has developed an intricate but robust and flexible plan to extract as many secrets from Ceres as possible, and they will take any changes in stride.

Each orbit is designed to provide a better view than the one before, and Dawn will map the orb thoroughly while at each altitude. The names for the orbits – rotation characterization 3 (RC3); survey; high altitude mapping orbit (HAMO); and low altitude mapping orbit (LAMO) – are based on ancient ideas, and the origins are (or should be) lost in the mists of time. Readers should avoid trying to infer anything at all meaningful in the designations. After some careful consideration, your correspondent chose to use the same names the Dawn team uses rather than create more helpful descriptors for the purposes of these blogs. That ensures consistency with other Dawn project communications. After all, what is important is not what the different orbits are called but rather what amazing new discoveries each one enables.

The robotic explorer will make many kinds of measurements with its suite of powerful instruments. As one indication of the improving view, this table includes the resolution of the photos, and the ever finer detail may be compared with the pictures during the approach phase. For another perspective, we extend the soccer ball analogy above to illustrate how large Ceres will appear to be from the spacecraft’s orbital vantage point.

Dawn code
Tentative dates (changes are guaranteed) Altitude
in miles
Resolution in
feet (meters)
per pixel
Resolution compared to Hubble Orbit
distance of
a soccer ball
1 RC3 April 23 –
May 9
24 15
10 feet
(3.0 meters)
Survey June 6-30 2,700
72 3.1
3.3 feet
(1.0 meters)
HAMO Aug 4 –
Oct 15
215 19
13 inches
(33 cm)
LAMO Dec 8 –
end of mission
850 5.5
3.3 inches
(8.5 cm)

As Dawn orbits Ceres, together they orbit the sun. Closer to the master of the solar system, Earth (with its own retinue, including the moon and many artificial satellites) travels faster in its heliocentric orbit because of the sun’s stronger gravitational pull at its location. In December, Earth was on the opposite side of the sun from Dawn, and now the planet’s higher speed is causing their separation to shrink. Earth will get closer and closer until July 22, when it will pass on the inside track, and the distance will increase again.

In the meantime, on April 12, Dawn will be equidistant from the sun and Earth. The spacecraft will be 2.89 AU or 269 million miles (433 million kilometers) from both. At the same time, Earth will be 1.00 AU or 93.2 million miles (150 million kilometers) from the sun.


Illustration of the relative locations (but not sizes) of Earth, the sun, Dawn and Ceres on April 12, 2015. (Earth and the sun are at that location every April 12.) The distance from Earth to Dawn is the same as the distance from the sun to Dawn. The images are superimposed on the trajectory for the entire mission, showing the positions of Earth, Mars, Vesta, and Ceres at milestones during Dawn’s voyage. Compare this to the arrangement in December, when Earth and Dawn were on opposite sides of the sun. Credit: NASA/JPL

It will be as if Dawn is at the tip of a giant celestial arrowhead, pointing the way to a remarkable solar system spectacle. The cosmos should take note! Right there, a sophisticated spaceship from Earth is gracefully descending on a blue-green beam of xenon ions. Finally, the dwarf planet beneath it, a remote remnant from the dawn of the solar system, is lonely no more. Almost 4.6 billion years after it formed, and 214 years after inquisitive creatures on a distant planet first caught sight of it, a mysterious world is still welcoming the new arrival. And as Dawn prepares to settle into its first close orbit, ready to discover secrets Ceres has kept for so long, everyone who shares in the thrill of this grand and noble adventure eagerly awaits its findings. Together, we look forward to the excitement of new knowledge, new insight and new fuel for our passionate drive to explore the universe.

Dawn is 35,000 miles (57,000 kilometers) from Ceres, or 15 percent of the average distance between Earth and the moon. It is also 3.04 AU (282 million miles, or 454 million kilometers) from Earth, or 1,120 times as far as the moon and 3.04 times as far as the sun today. Radio signals, traveling at the universal limit of the speed of light, take 51 minutes to make the round trip.

Dr. Marc D. Rayman
6:00 p.m. PDT March 31, 2015

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62 Responses to “Dawn Journal | March 31”

  1. Andrew R Brown. says:

    Hi Dr Marc and everyone,

    I have been away and also rather busy lately, so not had much opportunity to post.

    Love the crescent 1 Ceres RC3 images, I believe centred near enough on the south pole of the protoplanet. I suspect the images released so far are from near the beginning of RC3? The Where is DAWN shows 1 Ceres to be nearly full phase, at least a fat gibbous.

    I know most people are wondering about the exposed ice outcrops, the bright spots, but to me the biggest allures are the Pancake Crater and the south polar ‘graben’ or grooves.

    The images released so far show the grooves to not go all the way around, with the most seen on RC3 image 4. What is obvious on all as well as the rather nice OpNav 7 and RC2 images earlier on is that 1 Ceres landscape, generally reminds me of Mercury, with large craters, punctuated with smoother plains with smaller craters, much like the ‘Intercrater Plains’ discovered by Mariner 10 in 1974 and seen in great detail by the recently ended, enormously successful MESSENGER spacecraft. Also there appears to still be a lot of the Saturn moon Tethys and Uranus moons Umbriel and Oberon about 1 Ceres.

    Looking forward to seeing more also more later on during RC3.

    Andrew R Brown. Ashford, Kent, United Kingdom.

  2. Raúl says:

    Hello, Dr. Rayman.

    I’m enjoying so much this adventure, along all this years. Dawn, Rosetta, New Horizons, Juno, Curiosity, those wonderful machines are in the clímax of those epic quests in which you have invited all of us as spectators, with the amazing work of people like you and your team. As i talk with most of my friends, not very interested in space exploration until recent, i think that there’s a feeling of real discovery and exploration as i never have seen since the times of the Voyagers and Carl Sagan’s Cosmos. Brilliant engineering, brilliant science, brilliant effort, the brilliant blue glowing of the ion propulsion, feeding our thirst for knowledge, opening our minds and the “dawn”waking our imagination. That’s what the bright spots of Ceres are for me, at the moment.

    Congratulations and thank you.
    Brilliant blog.


  3. Mark says:

    Dr. Rayman,

    Does your team give consideration to the historical preservation of the spacecraft? I mean that before the mission is completed the last act would be to make sure the spacecraft is safe for perhaps hundreds of years. Does NASA have such a program? I can imagine that some of these orbiters would have historic and nostalgic value to future generations. And, if so, how is that balanced against the extraction of every bit of information gathering possible?


    • Marc Rayman says:

      Hi Mark,

      This is an interesting question. I agree that our interplanetary probes are (or will become) important historical artifacts, representing our species’ valiant attempts to reach out from the confines of our humble home to learn more about the cosmos. Actually, long before the mission is completed, we make sure the spacecraft will be safe after operations conclude. As I explained in August, we studied the final orbit quite extensively to ensure the spacecraft will not impact for many decades. The motivation was not preservation for historical purposes (as I described there, with some additional details in December), but the consequence is the same. So we will gather every bit of information we can, and I hope some future generations do appreciate that we have left a monument to humankind’s curiosity and ingenuity in orbit around the first dwarf planet discovered.


  4. Gareth says:

    Marc, I know you must be in your busiest time with the main science mission taking place right now at the RC3 orbit and with the slight communications breakdown which must have caused a few heart palpitations.
    The crater the spots are in seems to have a large round smooth jet black dome like structure on the edge of the crater closest the camera Is this just a trick of the light and angle the photograph was being taken from on the 14th of April?

    I guess you are now getting clearer pictures of everything so will everyone’s questions be answered by the 15th of May or will Dawn need to get to the Survey orbit height to confirm your suspicions??

    cheers Gareth

    • Marc Rayman says:

      Hi Gareth,

      I don’t see what you do in the pictures, but interpreting the structure of features only a pixel or a few pixels across is notoriously difficult (or impossible). Our visual system (mostly our brains, which process the images extensively, but also our eyes) are wired in ways that happened to provide survival advantages for our distant ancestors. They are not very good at analyzing views like this, in which we are seeing an alien world from an unusual perspective. In addition, a single pixel contains very little information.

      You can read the schedule in my text above for when pictures are taken and transmitted to Earth in RC3. The RC3 pictures will not confirm my suspicions. The reason is simple: I have no suspicions :-) That is, I have recognized all along that we cannot draw reliable conclusions about the shape, composition or structure of such small features from so few pixels. As I have been offering in comments for months, we await higher resolution images and other data. The RC3 pictures will tell us more, but I don’t know what they will tell us. The resolution will be about 1.65 times as good as the best we have so far. As my above table shows, survey will be better, HAMO better than that, and LAMO better than that. What is only one pixel across now will be nearly 60 pixels across by LAMO, and we will have neutron, gamma ray, visible and infrared spectra by then too. I have no doubt we will have many answers then. That, of course, is the reason for conducting this exciting mission! But I am much too ignorant to predict either what the answers will be or which data will answer specific questions.

      We’ll all find out as this adventure proceeds! I’m glad you remain so engaged.


  5. keith says:

    Congratulations on entering polar orbit! … hopefully JPL has a designated driver for Dawn … “Dawn Commences its Science Oribt” :)

  6. Marc, thanks for this awesome blog and the massive amount of information and knowledge in this post! It’s fantastic to make this available to everyone in the world. You could say it’s worthwhile because we as taxpayers are supporting it, but it’s also an effective and inspirational way to engage with people who can be our interplanetary explorers of tomorrow.
    I’d also like you to know I promoted your blog and borrowed a couple of your pictures (with full credit) on my blog, How To Be a Rocket Scientist. Here’s the direct link:
    Thanks even more for leading the historic Dawn mission with others at JPL and NASA!

    • Marc Rayman says:

      Thank you very much for your extremely kind comment and your interest, Brett! I also appreciate your own efforts to share such exciting work with others.


  7. Gareth says:

    Hi Marc,

    from the latest media releases it shows in infrared light that the two bright spots do not show up and yet other less bright areas thought to be ice as well, do show up. How is this possible? Frederica Tosi said you may not have enough resolution to see it in the proper way. What does that mean? Why would the resolution be okay for the other less bright spots but not be correct for the brighter ones??
    The intrigue of it all just keeps growing??
    Have they shown up in your April 14th navigational fix??

    • Marc Rayman says:

      Hi Gareth,

      For others, the media release Gareth refers to is here.

      The answers are not changed, but I will remind you. The pictures and other data Dawn has acquired so far are for a bonus, preliminary characterization of Ceres. The intent has been to gather enough information to prepare for RC3 observations, the first of the four intensive mapping campaigns. It should not be surprising that at this early stage, we do not have enough detail to reveal the answers. The composition of the bright spots is not known yet, and it certainly is too soon to say that any are ice (although some may turn out to have ice). In addition, the structure of the bright spots is not known yet. Therefore, we cannot say why they have the temperatures they do. But with regard to your question about how it can be possible, for a change our common experience here is quite applicable: different materials in our everyday experience have very different thermal properties (and may even be at very different temperatures under the same illumination conditions). There are myriad examples, including the difference between the temperature of sand and water on a beach or even a light car and a dark car after being in the sunlight. So, different regions on Ceres display different temperatures. As Dawn gets closer, we will learn more about the diverse nature of Ceres’ surface.

      Federico’s comment is related to the same one I have made here often. The spots are too small to show up clearly in our images and spectra (which is how we measure temperature). Let me offer a simple illustration. Imagine you use your camera to take a picture of Ceres. For that matter, it could also be the Statue of Liberty (unless you’re pretty nearby), Jupiter, Regulus (either the star or my cat, given that you aren’t very close to him), or any other object that presents a small angular size. No matter how much you enlarge the picture on your computer or smartphone, it will not show up as more than a single pixel. You can analyze it extensively, but there simply is not enough information there to learn about the actual shape or appearance. The bright spots are the same way. They are too small for Dawn’s camera or its spectrometers to see them as any more than one pixel at this distance. We need better resolution to understand all the bright spots, and that means we need to get closer. The finer the resolution, the more detail we can see, and that is why I have presented that important metric in the table above for the mapping orbits as well as the table in February for the earlier observations.

      The April 14 OpNav 7 has not taken place yet. The dates for the optical navigation sessions are for the beginning of the activity in the Pacific time zone. The spacecraft will not even begin its observations until about 11:52 PM PDT. Release of information will follow the usual process, which I mentioned most recently here. The release is through the JPL/NASA media relations office, not my blog comments. Pictures and other graphics will, as always, be posted here.

      Thank you for your continuing interest!


  8. Finiderire says:

    Dear Space Explorators,

    We are April 11th and still now update !?

    I have been patiently waiting for more than a month to have a glimpse at Ceres from never before distance !

    Wish you all the best. Hope to see them (very) soon.

    Best Regards,


    • Marc Rayman says:

      Thank you for your interest, Finiderire.

      I appreciate both your anticipation and your patience! As I have mentioned, the Dawn team is eager to share pictures promptly with the public. The science team has the responsibility of analyzing and interpreting the images for scientific publication. The need for accuracy and scientific review of the data slows the interpretation and release of the pictures.

      OpNav 6 executed flawlessly, and you won’t have to wait much longer.


  9. Guillaume Vollant-Boulé says:

    Hi Dr. Rayman,
    when I go to the data that as been uploaded to the site, I fing the fully calibrated images of Vesta at LAMO in .IMG files. I wonder how to open them? Because I tried to use Deamon Tools or burning a disk, but I seem unable to open them

    Thank you,
    Guillaume Vollant-Boulé

    • Marc Rayman says:

      Hi Guillaume,

      IMG is an image format, and there are free programs you can use to open such files (including NASAView). (It is also easily confused with the IMG format used for disk images, and many people see these when they install software.) As an alternative, all of the Vesta pictures are archived in JPEG (and other formats) here. (And, in case anyone is interested, the gravity measurements and the visible, infrared, gamma ray and neutron spectra are there as well.)


  10. Adam says:

    Hi Marc
    Thanks for this excellent journal – I’ve been a sporadic reader since launch day. When will the mass & physical dimensions of Ceres be updated by the latest data from DAWN?

    • Marc Rayman says:

      Hi Adam,

      I’ve been a sporadic writer since launch (and actually for more than a year prior to that). I’m glad you’ve been following the mission for so long.

      In my May Dawn Journal, I will give the mass and size of Ceres based on our RC3 measurements. We will continue to refine the values throughout the mission, however, as we gather more and more accurate data from lower altitudes.


  11. Rob says:

    Hi Marc, great blog, it just keeps getting better and better!

    I’m wondering whether the observation plans include getting a better handle on those orbit colors? Maybe point the spectro-doohickey on them for a full breakdown on what makes the blue one so different from the red?

    And I’ve done some extensive research online and still can’t find any references to names like “high altitude mapping orbit” in classical literature, but I haven’t given up yet! (I do like a challenge ;-) )

    Good luck with the mission,

    Cheers, Rob
    Bad Tölz,

    • Marc Rayman says:

      Thank you very much, Rob.

      I got a nice chuckle out of your message. (For others, lest you not recognize it, he is kidding.)


    • Romana Starfield says:

      Hey Rob, I think if you use the acronym instead of high altitude mapping orbit you will find lots of references in classical literature to HAMO. I refer you to the classics such as Shakespeare’s Hamolet and Dr Seuss’s Green eggs and Hamo. You need to diversify your reading sources my friend. ;)

      Sorry, I’ll go back to my box now.

  12. Gareth says:


    when looking again at the Feb 19 picture of the bright spots it would appear that there is two smaller brights spots in the smaller of the two spots and possibly three in the larger one.
    Have you been able to determine from closer examination of those Feb pictures if the two spots are made up of smaller bright spots.

    Also do you think that the April 14 navigational fix will show in more detail the bright spots if they are actually seen from the angle Dawn will be at, at that time.

    cheers……crazy pyramid man

    • Marc Rayman says:

      Hi Gareth,

      The pictures you are studying were processed to try to highlight details. That causes the bright spots to appear to be several pixels, but in reality, each is no more than one pixel. No meaningful conclusions can be drawn about the structure of the spots finer than a pixel. Therefore, we need pixels that cover a smaller area, and that is what we will get soon. We await the higher resolution pictures when Dawn is closer to reveal the nature of these intriguing features.

      As I wrote in my Dawn Journal above, we are not certain whether these bright spots will be in the illuminated region Dawn sees in its next navigation imaging window. We will find out when we look at the pictures! As I also described, however, we are going to obtain significantly better views early in May.

      Thank you for your continuing interest!


  13. Bill Clawson says:

    Is part of the reason for avoiding taking pictures of the dark side due to the possibility of catching a glimpse of the sun and burning out Dawn’s CCD? I’m only asking because of the extremely faint possiblity that their might be light sources on the surface of Ceres, or that any edge-wise volcanic eruptions might be visible, such as what was seen when Voyager passed Jupiter’s moon Io.

    • Marc Rayman says:

      Hi Bill,

      There are several reasons for not taking pictures on the dark side, as I explained in January: as you noted, we cannot safely point the camera that close to the sun, and we are conserving precious hydrazine for the many, many planned observations that are of higher scientific value. As you acknowledge, the possibility of seeing a source of light is exceedingly faint. There is no compelling reason to expect there to be one on Ceres, and we have a well-considered, scientifically sound program of exploration that makes the best use of hydrazine. Besides, as I described in this Dawn Journal above, we will get many observations of the limb in RC3, and because of the field of view of the camera, they will include the dark surface as well. So taking extra pictures on the dark side now would not be wise. In the end, we’ll obtain all those data without expending extra hydrazine now.

      I hope this brief reply answers your question.


  14. Chris Simundson says:

    Thanks again for taking the time to write these! I’m giving a quick presentation on Dawn in a few weeks to my class, so your posts are invaluable references.

    When do you anticipate switching on the reaction wheels?

    • Marc Rayman says:

      Hi Chris,

      I’m glad you find these to be useful. The answer to your question is here. In brief, we will switch on the reaction wheels when Dawn arrives in its final mapping orbit, which, as you can see from the table above, will be December.


      • Chris Simundson says:

        Ah, thank you.. I read that post and should have remembered it.
        Hope everyone on the Dawn team is enjoying the exploration!

  15. Chris Lea says:

    Thank you Doctor Mark,
    For all your brilliant journal updates over the past (very nearly 9 years now),

    Looking ahead, there’s a subject that’s popped up from time to time – mining the asteroids for their goodies.
    Is there going to be any likelihood that Vesta and Ceres have been ruled out of such ventures?
    Or does the protocol regarding planets prevent these two ‘giants’ of the asteroids from being exploited? I’d guess that any explorers (or exploiters) will start with something smaller to work on….or might they prefer to start on the biggest?

    Any thoughts on the subject – if you have time in between all your other myriad other works.

    Kind regards,


    • Marc Rayman says:

      Hi Chris,

      I’m delighted to know you’ve been following the mission for so long. It’s always a pleasure to meet someone who’s been onboard since this deep-space adventure began.

      I’m very interested in using extraterrestrial resources! Nevertheless, I will be brief here. The protocols (which we call “planetary protection“) are not as stringent at Vesta as they are at Ceres. It isn’t a matter of their being giants but rather other considerations related to their astrobiological interest. (After all, even Mercury doesn’t have strong protection requirements, and it’s still larger.) How the protocols might change for Ceres will depend on what we learn from Dawn’s exploration. Stay tuned!

      But there is a more important issue for answering your question. Vesta and Ceres are too difficult to get to for them to be attractive targets for mining for the foreseeable future. They are well beyond Mars (note their orbits in the last figure in my Dawn Journal above). And the tilt of their orbits (the “inclination”) is significantly greater, as I explained here, making them even more difficult to reach than you might conclude from that two-dimensional diagram. So although they likely contain resources that will be of great value to future explorers, it will be a very long time before Vesta or Ceres can be profitably exploited. Nearer term commercial exploitation will rely on objects much, much closer to Earth and significantly easier to get to.

      Thank you again for your interest.


  16. 1) Am enjoying your blog, Marc, and am looking forward to stereo pairs (or anaglyphs?) of Cere’s surface from the imaging we’ll get to see in May.

    2) Were the screen captures I took from your animated GIF (re:


    –the highest resolution, or can I download better images from that sequence?



    • Marc Rayman says:

      Thank you, Craig.

      Yes, the screen captures you have are the highest resolution we have released. I’m sure you’ll have fun with the images from May, and as I have described, Dawn will take many stereo images in its third mapping orbit.


  17. Matt Gibbons says:


    I’ll keep this short as I don’t want to add to your workload any more than necessary.

    Based on what you know regarding the bright spots, do you feel that meaningful imaging of them will take place during HAMO or LAMO? I’m assuming that RC3 and Survey are still too distant to resolve the bright spot features, whatever they are.

    Thanks for everything. I am now waiting patiently, and for the most part, quietly ;)


    • Marc Rayman says:

      I will be very brief, Matt. There is no doubt meaningful imaging will occur in every altitude. Dawn will fully map Ceres at every altitude. Even RC3 images will tell us more more about how small the bright areas are, and we will get more and more detail as we go lower.


  18. Giorgio La Rocca says:

    Hello Dr. Rayman
    and thank you so much for the intriguing updates.
    since my two little twin nieces’ names are on board of Dawn, I was worried they could have managed to change the flight path in some way! I’m kidding, it’s obvious.
    what I’m not kidding about, it’s the sense of hope I get everytime I read this blog. hope of a better future for all of us, bounded to this planet where so many evil things happen every day.
    please extend my deepest congratulations to all your team and in particular to all my fellow italian countrywomen and contrymen joining the project.

  19. tom says:

    dear marc,
    thanks for all the work you’ve put in this mission. i’ve been a fan since you did that shatner doc [here].
    In your work on ion drive & as the interplanetary flight engineer for dawn.

  20. Marc Rayman says:

    Fellow Dawnophiles,

    You will note I have scaled back my responses to blog comments in recent days, and I will be even less responsive for at least the next week. Nevertheless, I encourage all of you to continue posting comments and responding to each other. In fact, some questions come up so often, I’m sure many of you are just as capable of responding to them as I am :-) Meanwhile, rest assured that Dawn will be continuing to maneuver into its RC3 orbit, the talented and diligent members of the flight team will be working hard to ensure productive and rewarding operations, the experts on the science team will be continuing to study the data acquired so far, and the solar system will be continuing to perform its grand choreography. (And if there are any changes in any of those areas, JPL and NASA will let you know.)

    And if you hunger for more on this extraordinary extraterrestrial expedition, there is a wealth of information in the comments posted in recent months and, if you don’t mind my suggesting it, in previous Dawn Journals too!

    Thank you for your continuing interest.


  21. Frank Davis says:

    Reading through your blogs I was intrigued by the Feb 19 animation and the bright spots. As they rotated into the shadowed side of Ceres the bright spots stay very prominent even though the crater floor is in total darkness indicating that the spots may be quite tall, even more so than the crater walls. Has there been any thoughts on this? -Frank

    • Marc Rayman says:

      Hi Frank,

      The science team is analyzing all of the images to extract as much information as possible. They will release their findings when the appropriate scientific review is complete. Of course, what we really need are the higher resolution images. RC3 will help a great deal. And as I explained in my preview of the third mapping orbit (HAMO), we will acquire a great many stereo pictures to develop a topographical map (just as we did at Vesta). So we will not only have much higher resolution but we will really understand what the relative heights are.


  22. Johan Prins says:

    Thank you very much for the comprehensive blog reports, that are not only understandable for the layman (which over time I am not any more), but also the reports have a literary quality of style about them that is rare in the field of science reports.

    I am of course as curious as everyone to see more close-up pictures, and as a technician I cross all my fingers for the crew who runs this marvel for as long as it will work.

    It is sad that momentum wheeels are still a weak point in many a spacecraft. I thought that magnetical bearings had made their way into that field since I saw the prototype of a magnetic-bearing momentum wheel for an Amsat-satellite presented in 1996.

    My congratulations and encouragements go to those who built the probe and those who run it now.

    • Marc Rayman says:

      Thank you for your nice message, Johan!

      I have addressed related comments about momentum wheels (also known as reaction wheels) in recent months. You might be interested in this comment (and the link in it to previous comments).

      Regardless of the wheels, we have an exciting adventure to look forward to together!


  23. Daniel says:

    I have a question not directly relating to this blog post, hopefully you don’t mind.
    Is there any chance that Dawn will be put into “hibernation”, so to speak, in order to ensure some observations of Ceres close to perihelion? This is in case the Herschel water observations is a seasonal effect. I’m not entirely sure if it’s correct, but from my understanding Ceres is just about 3 years away from its next perihelion, so that would be April 2018. If the hydrazine ends up being pretty much used up by the end of the nominal mission in 2016, well, then Ceres is still quite far away.
    Maybe it’s a bit early to speculate about anything like that either way, you haven’t even really gotten to start with the observations yet. I could just hope that you will end up having enough hydrazine to last you all the way through to 2018 without any special arrangements and wish you luck!

    • John Blazy says:

      I was hoping there would be enough Hydrazine left after LAMO in December to help Dawn escape the gravitational pull from sending Dawn within 50 (?) miles of the bright spots for ultra close pics of those tantalizing crystals of wonder. I’m sure Marc will let us know how impossible/possible or improbable that will be.

      • Marc Rayman says:

        Hi John,

        LAMO starts in December, but it does not end then. However, we have good reasons not to let Dawn get any closer to Ceres, as I explained here. I am confident that the pictures and other data we plan to acquire on the bright spots will be terrific.


    • Marc Rayman says:

      Hi Daniel,

      Your idea sounds fun, but it is impossible. There are a great many technical obstacles to placing Dawn in hibernation for so long, but I cannot explain them here. The spacecraft was not designed for that, and it would not work. It also would not be a good use of this valuable explorer. As I’ve explained, it is not designed to study water vapor directly anyway. The best use of it is to squeeze as much out of the mission as we can now. Among the scientific investigations will be extensive searches for evidence on the surface of processes related to the sublimation of ice, cryovolcanism and interactions between the surface and subsurface water.


      • Daniel says:

        Thank you for your answer.

        Yeah, I was aware that Dawn isn’t really built to detect water vapour and if it can’t be put into hibernation, well, so be it. It’s a wonderful mission regardless. As I mostly read the blog rather than comment, I will add a thanks for the blog as well, it’s a pleasure to read it. Thank you!

  24. ran says:

    Thank you for the faciniting info !

  25. Barry Curtis says:

    What an exciting time it is. Mars, New Horizons, Dawn… What is going on at NASA is so exciting. Excellent update. Thank you. I’m so looking forward to the future discoveries of Dawn.

  26. Graham King says:

    Thanks for taking the time to blog these updates. I eagerly await the closer views, but meanwhile you have provided a very clear idea of just what is happening, when and why, and the prospects ahead. Graphics are exemplary! Great credit for shared work and Best wishes to all the Dawn team.

  27. Lawrence says:

    I cant wait for the lmao orbit

  28. Robert says:

    Has a prime meridian been set for Ceres? If not, how is it decided upon?

    • Marc Rayman says:

      Hi Robert,

      A prime meridian (that is, a choice of where 0 degrees longitude is) has been in use for telescopic observations of Ceres. The International Astronomical Union is the governing body, and they will decide upon updates based on Dawn’s mapping.


  29. Bill Kinsel says:

    Thank you, Dr. Rayman, for such an excellent and detailed explanation of what has been happening, and what will be happening in the upcoming weeks. Somewhat like the first commentator, I was puzzled by the lengthy silence about what was happening. I think that your diagram showing the orbital capture of Dawn, and how that prevents pictures from being taken for an extended period, helped answer that question.

    I am sure that we are all puzzled and intrigued by the “bright spots.” I wonder if the water vapor detected around Ceres is a product of geysers located at those bright spots, like at Enceladus.

    Bill Kinsel

  30. Gil Polanco says:

    Every time there’s a historical landing, orbit, contact, etc., we are inundated with photos, video, interviews, and news stories. Ever since the bright spots of Ceres made the news, there’s been silence from NASA. Dawn’s arrival was met with very little fanfare from the media. I Google Ceres in the news and look for recent close ups and there’s nothing. What’s going on? The mission to Eros got a heck of a lot more coverage.


    Gil Polanco

  31. Alan quayle says:

    Great blog, very informative. Ceres still seems to be active, wonder what the energy source is, possibly a higher portion of radioactive elements incorporated into its original formation, no tidal heating there, as for enceladus and europa

    • Marc Rayman says:

      Thank you, Alan.

      Whether Ceres is still active remains to be seen, but I’ll briefly mention one other energy source: solar heating. It obviously doesn’t extend deep, but it should not be ignored near the surface, especially at lower latitudes.


      • Alan quayle says:

        Yes solar heating must surely be at work here, the bright spots seem linked to the sun’s cycle, but there must be some mechanism for replenishing the ice, or whatever substance is causing the reflections, anyone got any ideas on this?

  32. Tim Hamblin says:

    Thank you Mark, for all your journal updates. It has been a very exciting journey so far and promises to be very remarkable in the coming months . I have been following Dawn’s approach and capture with Ceres very closely and appreciate all the excellent technical information you have been imparting. I have started to get my colleagues at work interested in Dawn’s progress. Again a big round of applause to your whole team . Best Reguards Tim.

  33. Guillaume Vollant-Boulé says:

    Haaaa Yisssssssssss!!!

    Hello Dr. Rayman,
    the soccer ball image is very good I must say, it gives a good sense of perspective. Thank you again for taking the time to right this blog. I might be a bit emmotionnal, but it gives me hope for space exploration when somebody care like you do. I must now continue waiting for the next pictures like you do, I’m sure.

    Until next time,
    Guillaume Vollant-Boulé