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Marc Rayman

Dawn Journal: A Bounty of Data

Posted by Marc Rayman

30-10-2015 20:22 CDT

Topics: mission status, asteroids, Dawn, asteroid 1 Ceres

Dear Exuldawnt Readers,

Dawn has completed another outstandingly successful campaign to acquire a wealth of pictures and other data in its exploration of dwarf planet Ceres. Exultant residents of distant Earth now have the clearest and most complete view ever of this former planet.

The stalwart probe spent more than two months orbiting 915 miles (1,470 kilometers) above the alien world. We described the plans for this third major phase of Dawn’s investigation (also known as the high altitude mapping orbit, or HAMO) in August and provided a brief progress report in September. Now we can look back on its extremely productive work.

Feature names on Ceres

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

Feature names on Ceres
This map of Ceres shows the feature names approved by the International Astronomical Union. We described the naming convention in December, and the most up-to-date list of names is here. The small crater Kait (named for the ancient Hattic grain goddess) is used to define the location of the prime meridian.

Each revolution, flying over the north pole to the south pole and back to the north, took Dawn 19 hours. Mission planners carefully chose the orbital parameters to coordinate the spacecraft’s travels with the nine-hour rotation period of Ceres (one Cerean day) and with the field of view of the camera so that in 12 orbits over the lit hemisphere (one mapping “cycle”), Dawn could photograph all of the terrain.

In each of six mapping cycles, the robot held its camera and its infrared and visible mapping spectrometers at a different angle. For the first cycle (Aug. 17-26), Dawn looked straight down. For the second, it looked a little bit behind and to the left as it completed another dozen orbits. For the third map, it pointed the sensors a little behind and to the right. In its fourth cycle, it aimed ahead and to the left. When it made its fifth map, it peered immediately ahead, and for the sixth and final cycle (Oct. 12-21) it viewed terrain farther back than in the third cycle but not as far to the right.

The result of this extensive mapping is a very rich collection of photos of the fascinating scenery on a distant world. Think for a moment of the pictures not so much from the standpoint of the spacecraft but rather from a location on the ground. With the different perspectives in each mapping cycle, that location has been photographed from several different angles, providing stereo views. Scientists will use these pictures to make the landscape pop into its full three dimensionality.

Dawn’s reward for these two months of hard work is much more than revealing Ceres’ detailed topography, valuable though that is. During the first and fifth mapping cycles, it used the seven color filters in the camera, providing extensive coverage in visible and infrared wavelengths.

False-color map of Ceres

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

False-color map of Ceres
This false-color map of Ceres was constructed using images taken in the first mapping cycle at an altitude of 915 miles (1,470 kilometers). It combines pictures taken in filters that admit light in what the human eye perceives as violet (440 nanometers), near the limit of visible red (750 nanometers), and invisible infrared (920 nanometers). Because humans are so good at processing visual information, depictions such as this are a helpful way to highlight and illustrate variations in the composition or other properties of the material on Ceres’ surface. Full image and caption.

In addition to taking more than 6,700 pictures, the spacecraft operated its visible and infrared mapping spectrometers to acquire in excess of 12.5 million spectra. Each spectrum contains much finer measurements of the colors and a wider range of wavelengths than the camera. In exchange, the camera has sharper vision and so can discern smaller geological features. As the nerdier among us would say, the spectrometers achieve better spectral resolution and the camera achieves better spatial resolution. Fortunately, it is not a competition, because Dawn has both, and the instruments yield complementary measurements.

Even as scientists are methodically analyzing the vast trove of data, turning it into knowledge, you can go to the Ceres image gallery to see some of Dawn’s pictures, exhibiting a great variety of terrain, smooth or rugged, strangely bright or dark, unique in the solar system or reminiscent of elsewhere spacecraft have traveled, and always intriguing.

Occator crater

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

Occator crater
Ten photos from Dawn’s first mapping cycle were combined to make this view centered on Occator crater. Because of the range of brightness, pictures with two different exposures were required to record the details of the bright regions and the rest of the crater itself, as explained last month. Eight additional pictures show the area around the crater. Occator is almost 60 miles (more than 90 kilometers) in diameter. Full image and caption.

Among the questions scientists are grappling with is what the nature of the bright regions is. There are many places on Ceres that display strikingly reflective material but nowhere as prominently as in Occator crater. Even as Dawn approached Ceres, the mysterious reflections shone out far into space, mesmerizing and irresistible, as if to guide or even seduce a passing ship into going closer. Our intrepid interplanetary adventurer, compelled not by this cosmic invitation but rather by humankind’s still more powerful yearning for new knowledge and new insights, did indeed venture in. Now it has acquired excellent pictures and beautiful spectra that will help determine the composition and perhaps even how the bright areas came to be. Thanks to the extraordinary power of the scientific method, we can look forward to explanations. (And while you wait, you can register your vote here for what the answer will be.)

Scientists also puzzle over the number and distribution of craters. We mentioned in December the possibility that ice being mixed in as a major component on or near the surface would cause the material to flow, albeit very slowly on the scale of a human lifetime. But over longer times, the glacially slow movement might prove significant. Most of Ceres’ craters are excavated by impacts from some of the many bodies that roam that part of the solar system. Ceres lives in a rough neighborhood, and being the most massive body between Mars and Jupiter does not give it immunity to assaults. Indeed, its gravity makes it even more susceptible, attracting passersby. But once a crater is formed, the scar might be expected to heal as the misshapen ground gradually recovers. In some ways this is similar to when you remove pressure from your skin. What may be a deep impression relaxes, and after a while, the original mark (or, one may hope, Marc) is gone. But Ceres has more craters than some scientists had anticipated, especially at low latitudes where sunlight provides a faint warming. Apparently the expectation of the gradual disappearance of craters was not quite right. Is there less evidence of flowing ground material because the temperature is lower than predicted (causing the flow to be even slower), because the composition is not quite what was assumed, or because of other reasons? Moreover, craters are not distributed as would be expected for random pummeling; some regions display significantly more craters than others. Investigating this heterogeneity may give further insight into the geological processes that have taken place and are occurring now on this dwarf planet.

Topographic map of Occator crater

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

Topographic map of Occator crater
This color-coded topographic map of Occator crater is based on Dawn’s observations in its second mapping orbit at an altitude of 2,700 miles (4,400 kilometers). Of course there is no sea level on Ceres, but the deep blue here is 5,150 feet (1,570 meters) below a reference level, and brown is 14,025 feet (4,275 meters) above it. (Brown is used in place of white for the elevation, so white can show the bright regions.) Imagine the exotic scenery here, with strangely bright areas and towering crater walls. The stereo views acquired in the third mapping orbit will reveal finer detail in the topography. Full image and caption.

Dawn’s bounty from this third major science campaign includes even more than stereo and color pictures plus visible and infrared spectra. Precise tracking of the spacecraft as it moves in response to Ceres’ gravitational pull allows scientists to calculate the arrangement of mass in the behemoth. Performing such measurements will be among the top three priorities for the lowest altitude orbit, when Dawn experiences the strongest buffeting from the gravitational currents, but already the structure of the gravitational field is starting to be evident. We will see next month how this led to a small change in the choice of the altitude for this next orbit, which will be less than 235 miles (380 kilometers).

The other top two priorities for the final mission phase are the measurement of neutron spectra and the measurement of gamma ray spectra, both of which will help in establishing what species of atoms are present on and near the surface. The weak radiation from Ceres is difficult to measure from the altitudes at which Dawn has been operating so far. The gamma ray and neutron detector (GRaND) has been in use since March 12 (shortly after Dawn arrived in orbit), but that has been to prepare for the low orbit. Nevertheless, the sophisticated instrument did detect the dwarf planet’s faint nuclear emissions even in this third orbital phase. The signal was not strong enough to allow any conclusions about the elemental composition, but it is interesting to begin seeing the radiation which will help uncover more of Ceres’ secrets when Dawn is closer.

To scientists’ great delight, one of GRaND’s sensors even found an entirely unexpected signature of Ceres in Dawn’s second mapping orbit, where the spacecraft revolved every 3.1 days at an altitude of 2,700 miles (4,400 kilometers). In a nice example of scientific serendipity, it detected high energy electrons in the same region of space above Ceres on three consecutive orbits. Electrons and other subatomic particles stream outward from the sun in what is called the solar wind, and researchers understand how planets with magnetic fields can accelerate them to higher energy. Earth is an example of a planet with a magnetic field, but Ceres is thought not to be. So scientists now have the unanticipated joy not only of establishing the physical mechanism responsible for this discovery but also determining what it reveals about this dwarf planet.

Northern hemisphere terrain on Ceres

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

Northern hemisphere terrain on Ceres
Dawn had this view near 0 degrees longitude in the northern hemisphere on Sept. 9 in its third mapping cycle at an altitude of 915 miles (1,470 kilometers). Oxo crater on the right, which shows bright material inside and out as well as a peculiar shape, is slightly over five miles (nearly nine kilometers) in diameter. The crater is named for the god of agriculture for the Yoruba people of Brazil.Full image and caption.

Several times during each of the six mapping cycles, Dawn expended a few grams of its precious hydrazine propellant to rotate so it could aim its main antenna at Earth. While the craft soared high above ground cloaked in the deep black of night, it transmitted some of its findings to NASA’s Deep Space Network. But Dawn conducted so many observations that during half an orbit, or about 9.5 hours, it could not radio enough data to empty its memory. By the end of each mapping cycle, the probe had accumulated so much data that it fixed its antenna on Earth for about two days, or 2.5 revolutions, to send its detailed reports on Ceres to eager Earthlings.

Following the conclusion of the final mapping cycle, after transmitting the last of the information it had stored in its computer, the robotic explorer did not waste any time gloating over its accomplishments. There was still a great deal more work to do. On Oct. 23 at 3:30 p.m., it fired up ion engine #2 (the same one it used to descend from the second mapping orbit to the third) to begin more than seven weeks of spiraling down to its fourth orbit. (You can follow its progress here and on Twitter @NASA_Dawn.) Dawn has accomplished more than 5.4 years of ion thrusting since it left Earth, and the complex descent to less than 235 miles (380 kilometers) is the final thrusting campaign of the entire extraterrestrial expedition. (The ion propulsion system will be used occasionally to make small adjustments to the final orbit.)

The blue lights in Dawn mission control that indicate the spacecraft is thrusting had been off since Aug. 13. Now they are on again, serving as a constant (and cool) reminder that the ambitious mission is continuing to power its way to new (and cool) destinations.

Dawn is 740 miles (1,190 kilometers) from Ceres. It is also 2.91 AU (271 million miles, or 436 million kilometers) from Earth, or 1,165 times as far as the moon and 2.93 times as far as the sun today. Radio signals, traveling at the universal limit of the speed of light, take 48 minutes to make the round trip.

Dr. Marc D. Rayman
3:00 p.m. PDT October 30, 2015

P.S. While the spacecraft is hard at work continuing its descent tomorrow, your correspondent will be hard at work dispensing treats to budding (but cute) extortionists at his front door. But zany and playful as ever, he will expand his delightful costume from last year by adding eight parts dark energy. Trick or treat!

See other posts from October 2015


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


Atom: 10/31/2015 02:23 CDT

Dr. Marc, Congradulations on all the wonderful achievements of this wonderful mission including the discovery of a magnetic field. Since Dawn lacks a magnetometer what is the inferred strength of the field from the available radiation data and was a similar feature observed at Vesta?

dougforworldsexplr: 10/31/2015 09:54 CDT

Dr. Marc, I am glad to hear that on this final orbit the neutron and gamma ray detectors will be used more. Will you be able to determine the composition of the bright spots in Occator crater and some of the other bright spots and if there is still some of the haze in Occator crater and if so when will we hear about it? Also will the general surface of Ceres be examined for indications it has some relation to Carbonaceous Chondrite asteroids or meteorites and will it be able to determine some of the specific organics there and isotopes and whether any Earth meteorites are from Ceres? When will we hear the results about some of these things? I appreciate this project and your work on it and your informative reports including on the Planetary Society blogs

Marc Rayman: 10/31/2015 10:52 CDT

Thank you both for your nice comments! The analysis of the energetic electrons is ongoing, and the physical mechanism for accelerating them has yet to be explained satisfactorily. It is too soon to provide answers. We did not observe the phenomenon at Vesta. I do not expect the nuclear spectra to reveal much directly about the bright regions. Even at Dawn's lowest altitude, those measurements will not yield spatial resolution fine enough. I expect the contributions to the spectral measurements from the bright material to represent such a tiny fraction that they will not be detected. Other methods (IR spectroscopy, images, geological context, etc.) should be more effective in elucidating the composition. Organics are notoriously difficult to identify in detail, and Dawn will not resolve different isotopes. Nevertheless, scientists will investigate all the questions you ask. Results will be reported when they are established and properly reviewed. I'm as eager as you to know the answers!

Josh: 10/31/2015 05:07 CDT

A possible magnetic field around a 900 km dwarf planet? Oh boy...if it is a magnetic field it would have to be internally generated, not like the induced fields around the galilean satellites. And that, in turn, implies Ceres' interior is MUCH warmer than thought possible even if it did completely differentiate. Then again, considering New Horizon's finding a geologically young pair of dwarf planets, one only barely larger than Ceres... Speaking of which, I have a suspicion the bright spots resulted from recent cryovolcanic activity - they seem to consist of salt (an expected evaporate from saltwater rising from the interior), they are always near cracks in the crust (much like the enceladus tiger stripes), their distribution does not strictly match a simple impact cause, similar salt is found in streaks covering Ceres' two pyramid shaped mountains (which would be hard if they weren't volcanoes...), and - if I recall correctly - salt on Ceres loses its brightness on the order of 40,000 yrs due to radiation. If current cryovolcanism is responsible, the reason the surface is not younger than it is likely relates to the fact that the water dominating the eruption is volatile on Ceres, eventually resulting in only some sublimation lag left behind to inefficiently 'fill' craters.

Josh: 10/31/2015 07:17 CDT

Side note...if it is indeed a magnetic field we have found, it means that Ceres isn't in hydrostatic equilibrium - the difference between its polar and equatorial axises is too high for an object with a metallic core (as would most likely be required if Ceres has a magnetic field), and thus Ceres' crust would have to have frozen while its rocks had not melted yet. May want to go back to the drawing board regarding the accretion times of icy objects...and whether accreting them too quickly causes them to boil off all their water.

Don Bailey: 10/31/2015 10:06 CDT

"The result of this EXTENSIVE mapping is a VERY RICH collection of photos of the FASCINATING scenery on a distant world". I find such writing irritating. But in Marc Rayman's comments of 10/31/2015 the writing is normal.

Atom: 11/01/2015 11:10 CST

Don, then don't read it. Dr. Marc has been doing these blogs for years. Not only are they informative and amusing but are a fine example to other mission teams for informing the public, which I frankly wish they would all do.

Arbitrary: 11/01/2015 11:23 CST

@Atom Indeed! ESA has at least two great missions going on now, Rosetta and Gaia, but it is inconceivable for their mission managers to blog about it like this. If someone says something, or even just wears the wrong shirt(!), he must cry in public and beg for pardon. Europe is not free. So everyone just shuts up and does as little as possible in order to avoid any responsibility.

paul Mccarthy: 11/02/2015 09:46 CST

Don: sorry, but must agree with Arbitrary. The adjectives and adverbs are required in order to nuance the nouns -- and give the sort of (relatively) finely-textured details about the mission that aren't available about many other missions.

Mortimer: 11/04/2015 02:55 CST

@Arbitrary : actually you must be misinformed about Rosetta, they have a very nice and educational blog here : ... so ok it's not written by our great Mark Rayman but still very good ! I agree ESA is not very good at PR ... their websites are most of the time a mess ... but they're working hard and becomming better with time, Rosetta is the perfect illustration of that ... i'm especially amazed at what they're doing with graphic design, cartoons even plush toys now, this is really cool and far better in the genre than anything i've ever seen from other space agencies.

ScienceNotFiction: 11/04/2015 03:34 CST

Dr. Rayman, I think you should take more close up LAMO photos on the OXO crater (I had referred it as "Stay-Tab" crater). This is gonna be the best chance for you to see what those strains are, and the crystal columns growing underneath the "tap". As for the other craters with root/liana structures, closer views will help us to see better of the shadows. Discovering possible roots or fibrous strains on Ceres will be a breakthrough in space exploration. I have already spotted scorpion-like creatures as well as a shrub-like bacterial plant on MRO's September photos (not just the "crab"). The possibility of plant or bacterial plants on Ceres and Mars is very high. There may be green plants inside Ceres near the crust ceiling, it will take a landing missing to find out in the future.

Sean: 11/04/2015 07:28 CST

Dr. Marc, Fascinating stuff! Congratulations! I enjoy your written exuberance but you do tease like a Dickens: " the physical mechanism for accelerating them has yet to be explained satisfactorily" I anxiously await next month's installment...

QubitsToy: 11/06/2015 12:52 CST

Thank you once again Exuldawnt Leader -- 6,700 pictures?? ok!

ScienceNotFiction: 11/24/2015 07:07 CST

Dear Dr. Rayman, Finally DAWN was able to take a photo from another angle on the fibrous crater in PIA20128. It is very exciting to confirm my initial observation that there are root-like materials casting shadows on the sun-lit side of the crater wall. This photo also shows the abundance of root-like lengthy materials suspending in mid air. This is the best visual proof of the existence of plant life (whether bacterial or photosynthetic).inside and outside of Ceres. Imagine trees(or liana) are growing upside down on the relatively thin crust ceiling inside the sandwiched air layer. They can provide oxygen to the environment which may form many types of oxides. The chemistry inside Ceres would bring new breakthroughs to the research of new material as well as biological research.

ScienceNotFiction: 12/10/2015 11:13 CST

Ammonium Salt (Ammonium Sulfate in particular) comes from the Cerean Mantle Based on much of my speculative theory about Ceres, the ammonium sulfate detected on the surface of Ceres is probably coming from the reaction of ammonia carbonate and gypsum (CaSO4·2H2O) and calcium carbonate precipitates as a solid and the ammonium sulfate solution may be mixed with other viscous material on the surface of Cerean ocean. During tidal surges, these material will flood near the surface crater and deposit the material all over Ceres. If ammonium sulfate exists on the surface of Ceres, we can be certain that plants/liana can grow inside the surface crust. With water, internal light (MgO plasma core), and naturally occurring fertilizer on Ceres, you can have giant trees growing underneath the surface upside down for hundreds/thousands of years. A landing exploratory mission to Ceres will be more fruitful than a mission to Mars. If we can discover plants on Ceres, the discovery of animal life forms will become obvious.

QubitsToy: 03/31/2016 08:42 CDT

All the info regarding geologic data is fascinating, but I am an architect, not trained in the sciences much past the introductory courses. That being said, I see this mission as a 3D festival. If we can't go to Ceres with a craft, we should be able to go there with a virtual reality. My efforts to make that possible are posted on YouTube and SketchFab. Please feel free to look at what I have been able to assemble with the limited data released so far. Thank you. animation - Real Time Model

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