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Marc Rayman

Dawn Journal: Success at Ceres

Posted by Marc Rayman

01-03-2016 7:04 CST

Topics: mission status, asteroids, asteroid 1 Ceres

Dear Indawnbitably Successful Readers,

A story of intense curiosity about the cosmos, passionate perseverance and bold ingenuity, a story more than two centuries in the making, has reached an extraordinary point. It begins with the discovery of dwarf planet Ceres in 1801 (129 years before its sibling Pluto; each was designated a planet for a time). Protoplanet Vesta was discovered in 1807. Following 200 years of telescopic observations, Dawn’s daring mission was to explore these two uncharted worlds, the largest, most massive residents of the main asteroid belt between Mars and Jupiter. And now, as of February 2016, the spacecraft has accomplished all of the objectives that NASA defined for it in 2004, even before construction began (and before the very first Dawn Journal, nearly a decade ago).

More than eight years after leaving its erstwhile planetary home behind for an ambitious deep space adventure, Dawn has now collected all of the data originally planned. Indeed, even prior to this third intercalary day of its expedition, the probe had already actually sent back a great deal more data for all investigations, significantly exceeding not only the original goals but also new ones added after the ship had set sail on the interplanetary seas. While scientists have a great deal of work still ahead to translate the bounty of data into knowledge, which is the greatest joy of science, the spacecraft can continue its work with the satisfaction that it has fulfilled its purpose and achieved an outstandingly successful mission.

Rim of Datan crater

NASA / JPL-Caltech / UCLA / MPS / DLR / IDA

Rim of Datan crater
Dawn took this picture of the rim of Datan crater on Jan. 7 in its fourth mapping orbit at 240 miles (385 kilometers). It flew over the same location on Oct. 2, 2015, in its third mapping orbit at 915 miles (1,470 kilometers). To see the improvement in detail, compare this with the earlier image (presented in November but reproduced below to make comparison easier). The bright material to the right of the crater rim here may help you locate this area within the wider image. Full image and caption.
Geshtin and Datan

NASA / JPL-Caltech / UCLA / MPS / DLR / IDA

Geshtin and Datan
Dawn took this picture in its third mapping orbit at an altitude of 915 miles (1,470 kilometers) in mapping cycle #5 of its third mapping orbit. The prominent triplet of overlapping craters nicely displays relative ages, which are apparent by which ones affect others and hence which ones formed later. The largest crater, Geshtin, is 48 miles (77 kilometers) across and is the oldest. (Geshtin is a Sumerian and Assyro-Babylonian goddess of the vine.) A subsequent impact that excavated Datan crater, which is 37 miles (60 kilometers) in diameter, obliterated a large section of Geshtin’s rim and made its own crater wall in Geshtin’s interior. (Datan is one of the Polish gods who protect the fields but apparently not this crater.) Still later, Datan itself was the victim of a sizable impact on its rim (although not large enough to have merited an approved name this early in the geological studies of Ceres). Full image and caption.

Dawn is the only spacecraft ever to orbit two extraterrestrial destinations, which would have been impossible without its advanced ion propulsion system. It is the only spacecraft ever to orbit an object in the main asteroid belt. It is also the only spacecraft ever to orbit massive bodies (apart from the sun and Earth) that had not been visited first by a flyby spacecraft to characterize the gravity and other properties. (By the way, Ceres is one of eight solar system bodies that operating spacecraft are orbiting now. The others are the sun, Venus, Earth, the moon, comet Churyumov-Gerasimenko, Mars and Saturn.)

Now in its fourth and final mapping orbit at Ceres, at an altitude of 240 miles (385 kilometers), Dawn is closer to the exotic terrain than the International Space Station is to Earth. The benefit of being in orbit is that the probe can linger rather than take only a brief look during a fast flyby. Even though Dawn has met its full list of objectives at Ceres, it continues to return new, valuable pictures and other measurements to provide even greater insight into this relict from the dawn of the solar system. For example, it is acquiring more nuclear spectra with its gamma ray and neutron detector, sharpening its picture of some atomic elements on Ceres. In addition, taking advantage of its unique vantage point, Dawn is collecting more infrared spectra of locations that are of special interest and soon will also take color photos and stereo photos (as it did in the third mapping orbit) of selected areas.

Dawn has completed more than 600 revolutions since taking up residence one year ago. The first few orbits took several weeks each, but as the spacecraft descended and Ceres’ gravitational embrace grew more firm, its orbital velocity increased and the orbital period decreased. Now circling in less than five and a half hours, Dawn has made 370 orbits since reaching this altitude on Dec. 7.

Ceres' southern high latitudes

NASA / JPL-Caltech / UCLA / MPS / DLR / IDA

Ceres' southern high latitudes
On Jan. 1, Dawn observed this scene at 78 degrees south latitude. This deep in the southern hemisphere, the sun is low on the horizon (it is three degrees north of the equator). The long shadows emphasize the topography in this densely cratered (and therefore old) region. Landslides are evident in the large crater wall on the left. Full image and caption.

The pace of observations here is higher than in the previous mapping orbits, where the orbital periods were longer. The spacecraft flies over the landscape faster now, and being closer to the ground, its instruments discern much more detail but capture a smaller area. Mission controllers have developed intricate plans for observing Ceres, but those plans depend on the spacecraft being at the right place at the right time. As we will see below, however, sometimes it may not be.

Suppose, for example, the intent is to observe a particular feature, perhaps the bright center of Occator crater, the lonely, towering mountain Ahuna Mons, the fractures in Dantu crater or artificial structures that definitively prove the existence of extraterrestrial intelligence, utterly transforming our understanding of the cosmos and shattering our naive perspectives on life in the universe. Trajectory analysis indicates when Dawn will fly over the designated location, and engineers will program it to take pictures or infrared spectra at that time. They will also include some margin, so they may program it to start 10 minutes before and end 10 minutes after. But they can’t afford to put in too much margin. Data storage on the spacecraft is limited, so other geological features could not be observed. Also, transmitting data to Earth requires pointing the main antenna at that distant planet instead of pointing sensors at Ceres, so it would be unwise to collect much more than is necessary.

Even if devoting additional time (and data) to trying to observe the desired place were feasible, it wouldn’t necessarily solve the problem. Dawn travels in a polar orbit, which is the only way to ensure that it passes over all latitudes. While Dawn soars from north to south over the sunlit hemisphere making its observations, the dwarf planet itself rotates on its axis, so the ground moves from east to west. If the spacecraft arrives at the planned orbital location a little early or a little late, the feature of interest may not even be beneath it but rather could be too far east or west, out of view of the instruments. In that case, increasing the duration of the observation period doesn’t help.

All of that is why, as we saw last month, it requires more pictures to fully map Ceres than you might expect. Many pictures may have to be taken in order to fill in gaps, and quite a few of the pictures overlap with others. Nevertheless, Dawn has done an excellent job. The spacecraft has photographed 99.6 percent of the dwarf planet from this low altitude. (If you aren’t regularly visiting the image gallery, you are missing out on some truly out-of-this-world scenes.)

Fluusa crater

NASA / JPL-Caltech / UCLA / MPS / DLR / IDA

Fluusa crater
Dawn photographed this scene on Jan. 4 as it was looking toward the horizon (as explained last month). Fluusa, the large crater from the center to the upper left is 37 miles (60 kilometers) in diameter. (Fluusa was a goddess of flowers for the Oscans of southern Italy who honored her to make plants bloom and bear fruit.) Its degraded features and dense cratering show it is old. Full image and caption.

The flight team devises very detailed plans that tell the spacecraft what to do every second, including where to point and what data to collect with each sensor. When the observation plans are developed, they are checked and double-checked. Then they are translated into the appropriate software that the robotic ship will understand, and these instructions are checked and double-checked. That is integrated with all the other software that will be beamed to the spacecraft covering the same period of time, any conflicts are resolved and then the final version is checked and, well, you know.

This process is very involved, and it is usually well over a month between the formulation and the execution of the plan. During that time, Dawn’s orbit can deviate slightly from the expert navigators’ mathematical predictions, preventing the spacecraft from flying over the desired targets. There are several reasons the actual orbit may differ from the orbit used for developing the plan. (We have seen related examples of this, including as Dawn approached Mars, when it orbited Vesta and when it spiraled from one mapping orbit to another.) Let’s briefly consider two.

One reason is that we do not have perfect knowledge of the variations in the strength of Ceres’ gravitational pull from one location to another. We have discussed before that measuring these tiny irregularities in the gravity field provides insight into the distribution of mass within the dwarf planet that gives rise to them. The team has mapped the hills and valleys of the field quite well and even better than expected. Still, the remaining small uncertainty can lead to slight differences between what navigators calculate Dawn’s motion will be and what its actual motion will be as it is buffeted by the gravitational currents.

A second source of discrepancy is that Dawn’s own activities distort its orbit. Every time the reaction control system expels a tiny burst of hydrazine to control the spacecraft’s orientation, keeping it pointed at its target, the force not only affects the orientation but also nudges the probe in its orbit, slowing it down or speeding it up very slightly. It’s up to the spacecraft to decide exactly when to make these small adjustments, and it is not possible for controllers to predict their timing. (In a similar way, when you are driving, you occasionally move the steering wheel to keep going the direction you want, even if is straight ahead. It would be impossible to forecast each tiny movement, because they all depend on what has already happened plus the exact conditions at the moment.) The details of the reaction control system activity also depend on the use of the novel hybrid control scheme, which the joint Orbital/JPL team developed because of the failure of two of the spacecraft’s four reaction wheels. The effect of each small firing of hydrazine is very small, but they can add up.

Unnamed craters on Ceres

NASA / JPL-Caltech / UCLA / MPS / DLR / IDA

Unnamed craters on Ceres
Dawn had this view of two unnamed craters on Jan. 1. The craters are about 10 miles (16 kilometers) and 3 miles (5 kilometers) in diameter. The distinct features show these are relatively young craters, not yet degraded by subsequent impacts or geological processes intrinsic to Ceres. The lighting in the craters shows that the sun is to the right, illuminating the left side of the depressions and missing the right side. Click on the image (or follow the link to the full image) and look carefully inside and around the larger crater. There are many small features that are light on the right and dark on the left. Therefore, they aren’t depressions like these two craters. Rather, they rise up, catching the light as it comes in from the right, and their left sides are in shadow. These are large blocks from the impact that excavated the crater. Each pixel in this picture is 120 feet (35 meters). Full image and caption.

It took about a month in this mapping orbit to discover many of the subtleties of the gravity field and gain experience with how hybrid control affects the orbit. But even before descending to this altitude, the operations team understood the nature of these effects and was well prepared to deal with them.

They devised several strategies, all of which are being used to good effect. One of the ways to account for Dawn’s actual orbit differing from its planned orbit is simply to change the orbit. Simply? Well, not really. It turns out to that to analyze the orbit and then maneuver to correct it in a timely way is a surprisingly complicated process, but, come to think of it, what isn’t complicated when flying a spaceship around a distant, alien world? Nevertheless, every three weeks, the flight team makes a careful assessment of the orbit and determines whether a small refinement with the ion propulsion system is in order. For technical reasons, if maneuvers are needed, they will be executed in pairs, so mission planners have scheduled two windows (each 12 hours long and separated by eight days) about every 22 days.

Adjustments to resynchronize the actual orbit with the predicted orbit that formed the basis of the exploration plan are known as “orbit maintenance maneuvers.” Succumbing to instincts developed during their long evolutionary history, engineers refer to them by an acronym: OMM. (As the common thread among team members is their technical training and passion for the exploration of the cosmos, and not Buddhism, the term is spoken by naming the letters, not pronouncing it as if it were a means of achieving inner peace. Instead, it may be thought of as a means of achieving orbital tranquility and harmony.)

For both Vesta and Ceres, trajectory analyses long in advance determined that OMMs would not be needed in the higher orbits, so no windows were included in those schedules. There have been three OMM opportunities since arriving at the lowest altitude above Ceres, but only the first was needed. Dawn performed the pair on Dec. 31-Jan. 1 and on Jan. 8 with its famously efficient ion engine. The orbit was good enough the next two times that OMMs were deemed unnecessary. It is certain that some future OMMs will be required. Your faithful correspondent provides frequent (and uncharacteristically concise) reports on Dawn’s day-to-day activities, including OMMs.

By the end of the Jan. 8 OMM, Dawn’s ion propulsion system had accumulated 2,019 days of operation in space, more than 5.5 years. During that time, the effective change in speed was 24,600 mph (39,600 kilometers per hour). (We have discussed in detail that this is not Dawn’s current speed but rather the amount by which the ion engines have changed it.) This is uniquely high for a spacecraft to accomplish with its own propulsion system and validates our description of ion propulsion as delivering acceleration with patience. (The previous record holder, Deep Space 1, achieved 9,600 mph, or 15,000 kilometers per hour.)

The effect of Dawn’s gentle ion thrusting during its mission has been nearly the same as that of the entire Delta II 7925H-9.5 rocket, with its nine external rocket engines, first stage, second stage and third stage. To get started on its interplanetary adventure, Dawn’s rocket boosted it from Cape Canaveral to out of Earth orbit with only four percent higher velocity than Dawn subsequently added on its own with its ion engines.

As Dawn and Earth follow their own independent orbits around the sun (Dawn’s now tied permanently to its gravitational master, Ceres), next month they will reach their greatest separation of the entire mission. On March 4 (about one Earth year after Ceres took hold of Dawn), on opposite sides of the solar system, they will be 3.95278 AU (367.434 million miles, or 591.328 million kilometers) from each other. (For those of you with full schedules, note that the maximum separation will be 5:40 a.m. PST.) They won’t be this far apart again until Feb. 6, 2025, long after Dawn has ceased operating (as discussed below). The figure below depicts the arrangement next month.

Dawn’s trajectory

NASA / JPL-Caltech

Dawn’s trajectory
Earth’s and Ceres’ orbits will bring them to their maximum separation on March 4. Earth’s orbit is shown in green and Ceres’ is in purple. Dawn’s interplanetary trajectory is in blue. Compare this figure with the ones depicting Dawn and Earth on opposite sides of the sun in December 2014, Dawn equidistant from Earth and the sun in April 2015, and Dawn and Earth at their minimum separation in July 2015. Also note that Earth has completed one full loop around the sun in the year since March 2015, when Dawn arrived at Ceres. During the same period, Ceres, traveling in a higher heliocentric orbit, has completed only about a fifth of a revolution.

Dawn has faced many challenges in its unique voyage in the forbidding depths of space, but it has surmounted all of them. It has even overcome the dire threat posed by the loss of two reaction wheels (the second failure occurring in orbit around Vesta 3.5 years and 1.3 billion miles, or 2.0 billion kilometers, ago). With only two operable reaction wheels (and those no longer trustworthy), the ship’s remaining lifetime is very limited.

A year ago, the team couldn’t count on Dawn even having enough hydrazine to last beyond next month. But the creative methods of conserving that precious resource have proved to be quite efficacious, and the reliable explorer still has enough hydrazine to continue to return bonus data for a while longer. Now it seems highly likely that the spacecraft will keep functioning through the scheduled end of its primary mission on June 30, 2016.

NASA may choose to continue the mission even after that. Such decisions are difficult, as there is literally an entire universe full of interesting subjects to study, but resources are more limited. In any case, even if NASA extended the mission, and even if the two wheels operated without faltering, and even if the intensive campaign of investigating Ceres executed flawlessly, losing not an ounce (or even a gram) of hydrazine to the kinds of glitches that can occur in such a complex undertaking, the hydrazine would be exhausted early in 2017. Clearly an earlier termination remains quite possible.

Regardless of when Dawn’s end comes, it will not be a time for regret. The mission has realized its raison d’être and is reaping rewards even beyond those envisioned when it was conceived. It has taken us all on a marvelous interplanetary journey and allowed us to behold previously unseen sights of distant lands. The conclusion of the mission will be a time for gratitude that it was so successful. And until then, every new picture or other measurement adds to the richly detailed portrait of a faraway, exotic world. There is plenty more still to do before this remarkable story draws to a close.

Dawn is 240 miles (385 kilometers) from Ceres. It is also 3.95 AU (367 million miles, or 591 million kilometers) from Earth, or 1,475 times as far as the moon and 3.99 times as far as the sun today. Radio signals, traveling at the universal limit of the speed of light, take one hour and six minutes to make the round trip.

Dr. Marc D. Rayman
5:00 p.m. PST February 29, 2016

See other posts from March 2016


Or read more blog entries about: mission status, asteroids, asteroid 1 Ceres


dougforworldsexplr: 03/01/2016 09:41 CST

Dear Marc; Thanks again for quite an interesting and informative article about the Dawn mission at Ceres. Although I am not generally too interested in the asteroids, I think especially Ceres is more interesting as by far the largest one, that it is circular and perhaps has some continuing internal activity such as possibly the hazes in Occator crater. My main interest of course is still about gathering some data about the chemical composition of Ceres. You mentioned in this article that Dawn is still gathering nuclear spectra data (both gamma ray and neutron radiation) and mentioned earlier that it has already gathered quite a lot of this data especially from its current lowest orbit. You mentioned it is quite difficult to gather data about organic chemicals when I mentioned that scientist knew before that Ceres is mostly a carbonaceous chondrite asteroid. Now has Ceres gathered any more nuclear spectra that allow you or any of the other Dawn scientists to better determine what organic chemicals are present or common on the surface of Ceres and any prominent isotopes including that could possibly be used to match any meteorites on Earth to Ceres as coming from there? Also has any of the nuclear spectra allowed you or any other of the Dawn scientists to determine the composition of the bright spots in Occator crater or other locations on Ceres beyond the determination of their chemical composition from only the brightness or other characteristics of the visual images? If these things haven't been determined how much possibility they can still be determined while Dawn is still operating or that they could be in the nuclear spectra data already collected by not sufficiently analyzed that would likely be analyzed later as it seems to me with NASA's limited budget and competing priorities for exploring other celestial bodies it could be a long time until NASA or any other space agency even gets another robotic probe to the vicinity of Ceres to study it further.

ChrisMan: 03/01/2016 10:32 CST

Why have we not seen any new images of the Occator crater since Dawn has reached it's final orbit?

spekny: 03/01/2016 12:44 CST

I just have to ask: Have you watched The Expanse on SyFy, and if so, what do you make of Ceres Station?

franklin: 03/01/2016 12:45 CST

Why is it that we have not seen pictures of the crater Ocator from a closer distant than thousands of miles? I would like to see it from the distance the Dawn satelite is actually now. PLEASE TELL US

Rockstar: 03/01/2016 03:17 CST

Obviously there is a conspiracy to cover up the true nature of Occator Crater. There is no logical reason to withhold the images. You know it Marc, and everyone else knows it. By your silence you have confirmed the cover up.

Marc Rayman: 03/01/2016 03:27 CST

Doug: I'm glad you found this interesting. Thank you. You may not be too interested in asteroids, but there is no particularly meaningful geophysical sense in which Ceres is an asteroid. That term is applied because of its location, not its properties. At any rate, I have addressed most of your questions in comments in previous months, but I'll offer some brief summaries here. The nuclear spectra reveal atoms but cannot identify organic chemicals. How the atoms combine to form molecules really is a different problem. Even with the other spectrometers that are sensitive to signals from molecules, organics are very difficult to identify. GRaND does not see features as small as Occator; its "pictures" are not that sharp. The best indicator of Occator composition will be from the infrared spectra (aided by the context of the visible + IR images), and when those results have gone through the normal scientific process and are ready for public release, we will release them. As with other NASA missions, all of Dawn's data will be released before the project concludes, so further analysis can be conducted by anyone, independent of any particular funding. I'm confident the Vesta and Ceres data will continue to be analyzed for a long time, and important new findings will come out of that regardless of whether the spacecraft is still operating.

Marc Rayman: 03/01/2016 03:43 CST

ChrisMan and Franklin: I appreciate your interest in Occator, and I understand your eagerness. We have released several images of it from our third mapping orbit at 915 miles. I mentioned in my Feb. 5 mission status report on the Dawn website that we were not even going to acquire our first picture of it in this fourth mapping orbit until late February. As I also explained there, we will release the pictures after following our normal process. Spekny: With my lifelong interest in space and a long interest in science fiction, I am eager to watch The Expanse. Dawn takes so much of my time, I just haven't gotten to it yet. I look forward to it! As with the mission itself (including pictures of Occator), not to mention life in general, I accept that I have to wait for some good things.

Mewo: 03/01/2016 03:50 CST

Congratulations on the official success of the mission. It must be exhilerating to know the mission has met its goals, and that everything from here is a bonus.

Marc Rayman: 03/01/2016 05:48 CST

Thank you very much, Mewo! You're exactly right. Orbiting and exploring both Vesta and Ceres has made for a long, complex, ambitious mission, and it is very gratifying indeed that it has worked out so well.

Chris Landau: 03/01/2016 06:22 CST

Hi Mark I do not understand why the northern part of Datan crater arc has left the older Geshtin crater rim intact. Also it is oval, not the usual shape for an impact feature or a caldera. Your thoughts? Chris Landau March 1, 2016

Atom: 03/01/2016 06:27 CST

Congratulations to the entire Dawn team for all the cumulative successes of this remarkable mission. Thank you Dr. Marc for all your timely updates. Since I began following this mission before launch including a mission cancellation, your achievements are even more impressive! Would you please comment on the gravity subtleties you mentioned. Are there any mascons or are the subtleties mostly the result of the extreme topography?

Chris Landau: 03/01/2016 06:52 CST

Hi Marc Sorry about that last spelling mistake. What is going on in the photo of Cers' southern high latitudes of s folds and polygonal structures. Perhaps your geological team would like to comment. Slumping on the crater wall does not do justice for an explanation. Thanks Chris Landau March 1, 2016

Pasander: 03/01/2016 07:00 CST

So, if all of the science objectives have been achieved, why not take it even lower? I am thinking about getting even higher resolution images of the most interesting features (like Occator).

Mark H: 03/02/2016 01:41 CST

Hi Marc: I found your article to be a lot more than "quite" interesting - your writing style is addictive for us readers and full of the detail which we space loons soak up like sponges. Thanks so much. However , ... "or artificial structures that definitively prove the existence of extraterrestrial intelligence, utterly transforming our understanding of the cosmos and shattering our naive perspectives on life in the universe." ... this paragraph is going to land us in trouble! Next minute, the red-top media will be saying that a NASA official has confirmed it is looking for artificial intelligence on Ceres! You know what the trollers are like. I loved it though; so tongue-in-cheek and so casually tossed into the article. Marvellous! Thanks so much. Keep up the good work for us.

Marc Rayman: 03/02/2016 09:02 CST

Sorry to be slow in responding… Chris: After discussion within the team, geological conclusions are reported in scientific papers and conferences as well as in formal JPL/NASA news releases, but the team doesn't release specific scientific results in blog comments. I have my own thoughts, but I would leave it to you and others to provide and discuss your ideas. Atom: Thank you for your nice comment. I'm glad you've been following the mission for so long! There may well be mascons, but Dawn's gravity investigation does not have the spatial resolution to detect such small features. But the subtleties are not exclusively the result of topography. Rather, they are the result of the interior structure, and that's what will allow fascinating insights into the nature of this dwarf planet. Pasander: Our assessment is that going a little closer doesn't provide a benefit that's worth the tremendous cost in hydrazine (the consumption of which goes up very quickly at lower altitudes), significant operational complexities, increased image smear from the higher orbital velocity, and other technical complications. I mentioned in my Aug. 2014 Dawn Journal (search for Omnipodawnt) our constraints on planetary protection that preclude us from getting too close, where subsequent contact might become a risk. Mark H: I greatly appreciate your very kind remarks. Thank you. The "trollers" won't be as fond of what you wrote, but they make up their own minds without the constraints of rational thought anyway. Sigh. At least they can serve as a source of humor.

bertrout: 03/03/2016 05:31 CST

I've read a number of your blogs over the last few months Marc. They are by far the most informative articles on the Ceres Dawn mission. Thank you for sharing your thoughts and expertise. I have come to expect a thorough approach and a lot of details from your blog which is why I'm so frustrated by your apparent gag order on the only details anyone really wants to see, namely the Occator crater and the large pyramid-shaped mountain feature. It would be one thing to say "we're studying the pictures" or "we don't know what the features are" but to go silent like when Dawn went into safe mode is not lending credibility to your science. I've heard the twitter handle for Dawn suggest that pictures would be "processed in a month" as though somehow though 2 distant features were the only 2 areas that would take so long to return data. I feel like I'm watching Showgirls on TBS: all the best parts are being blocked out. At this point you're only catering to conspiracy theorists. No matter what deductions you make they will be questioned forever due to your gaffs and preposterous guesses as to the nature of those features. It flies in the face of your excellent and provably scientific mission. It makes your whole team look silly. It's time to start talking. It's time to admit your theories of salt deposits, ice and (trying not to snort laugh) sunlight reflection were erroneous. Please explain yourself.

Marc Rayman: 03/04/2016 12:47 CST

bertrout: Thank you for your feedback. Think what you will. I actually have no obligation to present any information on Dawn nor to explain why or how I choose what to write about. My responsibility is to run the Dawn mission. As I described in a blog on the Dawn website in May 2014, I write these Dawn Journals in my limited spare time. It is purely voluntary, and so I do it the way I like doing it. If readers don't find what they want, that's OK. At any rate, I described our best understanding to date of Occator crater in my December Dawn Journal (search for "Transcendawnts"), and I have often mentioned the process for the release of information. In Dawn Journals going all the way back to launch in 2007 (and actually to 1.5 years before launch), I've presented the most complete description of all aspects of the mission that I can. I may not write about some events as quickly as you would like. I will not comment further on these kinds of topics. I have been interested for my whole life in the exploration of space. That is where I will devote my time and energies.

Paul McCarthy: 03/04/2016 11:47 CST

Good response Dr Rayman. Perfectly understandable. As they say: "You can please all of the people some of the time, ...". I find this in my own little public endeavours (non space-related) -- that people are amazingly blunt and harsh even when one is doing them a favour and working hard for them. The internet seems to have made it worse. Great updates throughout the exciting Dawn journey.

bertrout: 03/05/2016 05:20 CST

Thanks for responding Marc. My goal was not to upset you nor do I hold you personally responsible for disseminating info on the Dawn mission.Perhaps you could direct me to who IS responsible for this obvious withholding of information about important features. As of 2007 the Dawn program had cost $446 million and as such, yes someone certainly does have an obligation to share teh results of that mission with the public. At any rate my beef is more with this behavior of secrecy especially in light of the very strong opinions presented, including my you, as the the nature of the bright spots on Ceres. I apologize if you were personally offended. I want the same answers as everyone else even if some don't have the guts to say it to you. Good luck with your mission and congratulations on reaching all your objectives. It's been a fun ride.

dougforworldsexplr: 03/05/2016 07:11 CST

Thanks too for responding Marc. Sorry if I bothered you for being insistent for asking some of the information about both Occator Crater and about evidence of organics on Ceres. It wasn't you but really NASA in general I was frustrated with as I am sure there won't be another space mission to Ceres anytime soon and that NASA would be aware of that before and that it was also known a long time ago that Ceres was usually classed as a carbonaceous chondrite asteroid likely to have organics and at least since 2008 that I have a book with copyright date with a Hubble picture of Ceres that there was a bright spot at Occator Crater so that perhaps more could have been foreseen and done beforehand by NASA to include more sensitive infrared instruments to do chemical determination of compounds in these places. Anyway thank for your many thoughtful and considerate comments during the DAWN mission and all the best for your future in the space program.

Sean: 03/05/2016 12:11 CST

Dr. Marc, My sympathies, however it has to be somewhat exhilarating to see your amazing discoveries met with such eagerness by the public. Any of us who have chatted of posted comments on the web can also understand how daunting the human maelstrom provoked by NASA/JPL’s success with social media must be. That said, a statement in your most recent reply to an overly enthused Occator Crater enthusiast, “I will not comment further on these kinds of topics,” has provoked this amateur to urge calm and to overlook the sometimes crass and pop public interests fanned not just by your marvelous discoveries but the language of your own excitement. (Those JPL retro space travel posters seem to cater to this pop interest in your own institutions desires for digital eyeballs.) So, Doc, please, continue to sate my desire for discovery and adventure in as unexpurgated a fashion as you are able including the primordial volatiles, the high energy electrons, The Lonely Mountain (NASA’s words according to and, of course, Occator Crater and anything else you, your team and your amazing spacecraft are yet to discover.

Bob Ware: 03/08/2016 08:12 CST

Thank you Dr. Marc for another informative article on this glorious mission!

Bob Ware: 03/08/2016 08:27 CST

When scientists write their findings in a public class domain like TPS or a newspaper or general magazine they need to abide by constraints of the science community. Specifically they are not to release information that other team members are working on that have copyright protections and other professional boundaries. Like it or not, that's they way it is. Eventually this information comes out in a published format and at that time you can buy it (usually) fairly low cost. Also, by that time the science or theories are understood fairly well and you get a good education out of the reading. I did theoretical research with materials on propulsion in the early to mid 90's and simultaneously NASA did the exact same thing without either of us knowing it. We came to the same conclusions but I was harry homeowner scale and they were the big boy scale. There is some serious personal satisfaction in that! I kept the lid on what I was doing to protect my ideas until I could make it work. I had accidentally "created" another idea which has a tightly sealed lid on it still. If I can get that idea to work .... !!!

ScienceNotFiction: 04/23/2016 09:22 CDT

Dr. Raymond, I'm still very fascinated by Dawn's latest photos and what your team has accomplished so far. I hope all of my previous suggestions and unconfirmed theories about Ceres would aid your team to look at all possibilities. Occator's closing up was long predicted by me last year. OXO is our only hope to peek into the interior layer of Ceres at this time. Of course, there are other tiny cracks/holes on the surface for exploration by landing mission in the future. The fibrous strains that prevented the total collapse of OXO basin are very intriguing indeed. The bright light coming from the core makes visual study difficult. One thing is certain, these fibrous strains looked elastic in nature, perhaps composed of silicone-like materials. I strongly suspect a layer of this material is beneath the surface crust of Ceres that can prevent major surface collapse from impacts. The gas layer keeps the internal pressure of Ceres in a balance. The impact openings of Occator few years ago has disrupted this balance and naturally occurring gel-like chemical compound had surged up to fill the cracks and openings. Before the Occator opening, the air pressure had prevented gel-like chemical to rise up due to lowering of gas production from layers near the core.

ScienceNotFiction: 04/23/2016 09:48 CDT

Dr. Raymond, Is there any LAMO photos on the crater shown in PIA20133. This is the one that I have seen another photo that shadows of liana-like arches were projected upon the crater slope on the opposite side. A closer view may reveal more details. This will prove that some kind of branches (biological or non-biological) exists on Ceres. I think this crater has not been named.

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