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Marc Rayman

Dawn Journal: 8 Years in Space

Posted by Marc Rayman

28-09-2015 7:49 CDT

Topics: asteroid 4 Vesta, mission status, asteroids, Dawn, asteroid 1 Ceres

Dear Dawnniversaries,

Eight years ago today, Dawn was gravitationally bound to a planet. It was conceived and built there by creatures curious and bold, with an insatiable yearning to reach out and know the cosmos. Under their guidance, it left Earth behind as its Delta rocket dispatched it on an ambitious mission to explore two of the last uncharted worlds in the inner solar system. As Earth continued circling the sun once a year, now having completed eight revolutions since its celestial ambassador departed, Dawn has accomplished a remarkable interplanetary journey. The adventurer spent most of its anniversaries powering its way through the solar system, using its advanced and uniquely capable ion propulsion system to reshape its orbit around the sun. On its way to the main asteroid belt, it sailed past Mars, taking some of the that red planet’s orbital energy to boost its own solar orbit. On its fourth anniversary, the probe was locked in orbit around the giant protoplanet Vesta, the second most massive object between Mars and Jupiter. Dawn’s pictures and other data showed it to be a complex, fascinating world, more closely related to the terrestrial planets (including one on which it began its mission and another from which it stole some energy) than to the much smaller asteroids.

Dawn launches

KSC / NASA

Dawn launches
Dawn launched at dawn (7:34 a.m. EDT) from Cape Canaveral Air Force Station, Sep. 27, 2007. Its mission is to learn about the dawn of the solar system by studying Vesta and Ceres. The intricate sequence of activities between the time this photo was taken and Dawn’s separation from the rocket to fly on its own is described here.

Today, on the eighth anniversary of venturing into the cosmos, Dawn is once again doing what it does best. In the permanent gravitational embrace of dwarf planet Ceres, orbiting at an altitude of 915 miles (1,470 kilometers), Dawn is using its suite of sophisticated sensors to scrutinize this mysterious, alien orb. Ceres was the first dwarf planet ever sighted (and was called a planet for more than a generation after its discovery), but it had to wait more than two centuries before Earth accepted its celestial invitation. The only spacecraft ever to orbit two extraterrestrial destinations, this interplanetary spaceship arrived at Ceres in March to take up residence.

Although this is the final anniversary during its scheduled primary mission, Dawn will remain in orbit around its new home far, far into the future. Later this year it will spiral down to its fourth and final orbital altitude at about 230 miles (375 kilometers). Once there, it will record spectra of neutrons, gamma rays, and visible and infrared light, measure the distribution of mass inside Ceres, and take pictures. Then when it exhausts its supply of hydrazine next year, as it surely will ,the mission will end. We have discussed before that despite the failure of two reaction wheels, devices previously considered indispensable for the expedition, the hardy ship has excellent prospects now for fulfilling and even exceeding its many goals in exploring Ceres.

Last month we described the plans for Dawn’s penultimate mapping phase at the dwarf planet, and it is going very well. The probe is already more than halfway through this third orbital phase at Ceres, which is divided into six mapping cycles. Each 11-day cycle requires a dozen flights over the illuminated hemisphere to allow the camera to map the entire surface. Each map is made by looking at a different angle. Taken together then, they provide stereo views, so scientists gain perspectives that allow them to construct topographical maps. The camera’s internal computer detected an unexpected condition in the third cycle of this phase, and that caused the loss of some of the pictures. But experienced mission planners had designed all of the major mapping phases (summarized here) with more observations than are needed to meet their objectives, so the deletion of those images was not significant. At this moment, the spacecraft is nearing the end of its fourth mapping cycle, making its tenth flight over the side of Ceres lit by the sun.

You can follow Dawn’s progress by using your own interplanetary spaceship to snoop into its activities in orbit around the distant world, by tapping into the radio signals beamed back and forth across the solar system between Dawn and the giant antennas of NASA’s Deep Space Network, or by checking the frequent mission status reports.

You also can see the marvelous sights by visiting the Ceres image gallery. Among the most captivating is Occator crater (see the picture below). As the spacecraft has produced ever finer pictures this year, starting with its distant observations in January, the light reflecting from the interior of this crater has dazzled us. The latest pictures show 260 times as much detail. Dawn has transformed what was so recently just a bright spot into a complex and beautiful gleaming landscape. Last month we asked what these mesmerizing features would reveal when photographed from this the present altitude, and now we know.

Occator Crater, Ceres

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

Occator Crater, Ceres

Dawn’s view of Occator crater from an altitude of 915 miles (1,470 kilometers). This is a composite of two photos taken on Aug. 22. Because of the large range in brightness, controllers modified Dawn’s observation plan to take pictures with different exposures: a normal exposure for most of the scene, and a short exposure to capture the details of the brightest areas. Occator is almost 60 miles (more than 90 kilometers) in diameter. Following the theme established last year for naming features on Ceres, the International Astronomical Union named this crater for a Roman deity of harrowing. Whatever the geochemical reason for the stunning bright regions turns out to be, it’s unlikely to be related to that agricultural technique of breaking up soil and covering seeds. Full image and caption.

Scientists are continuing to analyze Dawn’s pictures and other data not only from Occator but all of Ceres to learn more about the nature of this exotic relict from the dawn of the solar system. Many deep questions are unanswered and remain mystifying, but of one point there can be no doubt: the scenery is beautiful. Even now, the photos speak for themselves, displaying wondrous sights on a world shaped both by its own complex internal geological processes as well as by external forces from more than 4.5 billion years in the rough and tumble main asteroid belt.

Because the pictures speak for themselves, your correspondent will speak for the mission. So now, as every Sep. 27, let’s take a broader look at Dawn’s deep-space trek. For those who would like to track the probe’s progress in the same terms used on past anniversaries, we present here the eighth annual summary, reusing text from previous years with updates where appropriate. Readers who wish to reflect upon Dawn’s ambitious journey may find it helpful to compare this material with the logs from its first, second, third, fourth, fifthsixth and seventh anniversaries.

In its eight years of interplanetary travels, the spacecraft has thrust for a total of 1,976 days, or 68 percent of the time (and about 0.000000039 percent of the time since the Big Bang). While for most spacecraft, firing a thruster to change course is a special event, it is Dawn’s wont. All this thrusting has cost the craft only 873 pounds (396 kilograms) of its supply of xenon propellant, which was 937 pounds (425 kilograms) on Sep. 27, 2007. The spacecraft has used 66 of the 71 gallons (252 of the 270 liters) of xenon it carried when it rode its rocket from Earth into space.

The thrusting since then has achieved the equivalent of accelerating the probe by 24,400 mph (39,200 kilometers per hour). As previous logs have described (see here for one of the more extensive discussions), because of the principles of motion for orbital flight, whether around the sun or any other gravitating body, Dawn is not actually traveling this much faster than when it launched. But the effective change in speed remains a useful measure of the effect of any spacecraft’s propulsive work. Having accomplished 98 percent of the thrust time planned for its entire mission, Dawn has far exceeded the velocity change achieved by any other spacecraft under its own power. (For a comparison with probes that enter orbit around Mars, refer to this earlier log.) The principal ion thrusting that remains is to maneuver from the present orbit to the final one from late October to mid-December.

Dawn's trajectory

NASA / JPL-Caltech

Dawn's trajectory
Dawn’s interplanetary trajectory (in blue). The dates in white show Dawn’s location every Sep. 27, starting on Earth in 2007. Note that Earth returns to the same location, taking one year to complete each revolution around the sun. When Dawn is farther from the sun, it orbits more slowly, so the distance from one Sep. 27 to the next is shorter.

Since launch, our readers who have remained on or near Earth have completed eight revolutions around the sun, covering 50.3 AU (4.7 billion miles, or 7.5 billion kilometers). Orbiting farther from the sun, and thus moving at a more leisurely pace, Dawn has traveled 35.0 AU (3.3 billion miles, or 5.2 billion kilometers). As it climbed away from the sun, up the solar system hill, to match its orbit to that of Vesta, it continued to slow down to Vesta’s speed. It had to go even slower to perform its graceful rendezvous with Ceres. In the eight years since Dawn began its voyage, Vesta has traveled only 32.7 AU (3.0 billion miles, or 4.9 billion kilometers), and the even more sedate Ceres has gone 26.8 AU (2.5 billion miles, or 4.0 billion kilometers). (To develop a feeling for the relative speeds, you might reread this paragraph while paying attention to only one set of units, whether you choose AU, miles, or kilometers. Ignore the other two scales so you can focus on the differences in distance among Earth, Dawn, Vesta and Ceres over the eight years. You will see that as the strength of the sun’s gravitational grip weakens at greater distance, the corresponding orbital speed decreases.)

Mountain on Ceres

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

Mountain on Ceres
Dawn had this view on Aug. 18 from an altitude of 915 miles (1,470 kilometers). The unnamed mountain to the right of center reaches a height of 4 miles (6 kilometers) or 20,000 feet. This curious cone, showing prominent bright streaks, has a sharply defined base with virtually no accumulated debris. We have seen this huge feature from other perspectives in previous months. Full image and caption.

Another way to investigate the progress of the mission is to chart how Dawn’s orbit around the sun has changed. This discussion will culminate with a few more numbers than we usually include, and readers who prefer not to indulge may skip this material, leaving that much more for the grateful Numerivores. (If you prefer not to skip it, click here.) In order to make the table below comprehensible (and to fulfill our commitment of environmental responsibility), we recycle some more text here on the nature of orbits.

Orbits are ellipses (like flattened circles, or ovals in which the ends are of equal size). So as members of the solar system family (including Earth, Vesta, Ceres and Dawn) follow their paths around the sun, they sometimes move closer and sometimes move farther from it.

In addition to orbits being characterized by shape, or equivalently by the amount of flattening (that is, the deviation from being a perfect circle), and by size, they may be described in part by how they are oriented in space. Using the bias of terrestrial astronomers, the plane of Earth’s orbit around the sun (known as the ecliptic) is a good reference. Other planets and interplanetary spacecraft may travel in orbits that are tipped at some angle to that. The angle between the ecliptic and the plane of another body’s orbit around the sun is the inclination of that orbit. Vesta and Ceres do not orbit the sun in the same plane that Earth does, and Dawn must match its orbit to that of its targets. (The major planets orbit closer to the ecliptic, and part of the arduousness of Dawn’s journey has been changing the inclination of its orbit, an energetically expensive task.)

Now we can see how Dawn has done by considering the size and shape (together expressed by the minimum and maximum distances from the sun) and inclination of its orbit on each of its anniversaries. (Experts readily recognize that there is more to describing an orbit than these parameters. Our policy remains that we link to the experts’ websites when their readership extends to one more elliptical galaxy than ours does.)

The table below shows what the orbit would have been if the spacecraft had terminated ion thrusting on its anniversaries; the orbits of its destinations, Vesta and Ceres, are included for comparison. Of course, when Dawn was on the launch pad on Sep. 27, 2007, its orbit around the sun was exactly Earth’s orbit. After launch, it was in its own solar orbit.

Minimum distance
from the Sun (AU)
Maximum distance
from the Sun (AU)
Inclination
Earth’s orbit 0.98 1.02 0.0°
Dawn’s orbit on Sep. 27, 2007 (before launch) 0.98 1.02 0.0°
Dawn’s orbit on Sep. 27, 2007 (after launch) 1.00 1.62 0.6°
Dawn’s orbit on Sep. 27, 2008 1.21 1.68 1.4°
Dawn’s orbit on Sep. 27, 2009 1.42 1.87 6.2°
Dawn’s orbit on Sep. 27, 2010 1.89 2.13 6.8°
Dawn’s orbit on Sep. 27, 2011 2.15 2.57 7.1°
Vesta’s orbit 2.15 2.57 7.1°
Dawn’s orbit on Sep. 27, 2012 2.17 2.57 7.3°
Dawn’s orbit on Sep. 27, 2013 2.44 2.98 8.7°
Dawn’s orbit on Sep. 27, 2014 2.46 3.02 9.8°
Dawn’s orbit on Sep. 27, 2015 2.56 2.98 10.6°
Ceres’ orbit 2.56 2.98 10.6°

For readers who are not overwhelmed by the number of numbers, investing the effort to study the table may help to demonstrate how Dawn has patiently transformed its orbit during the course of its mission. Note that four years ago, the spacecraft’s path around the sun was exactly the same as Vesta’s. Achieving that perfect match was, of course, the objective of the long flight that started in the same solar orbit as Earth, and that is how Dawn managed to slip into orbit around Vesta. While simply flying by it would have been far easier, matching orbits with Vesta required the exceptional capability of the ion propulsion system. Without that technology, NASA’s Discovery Program would not have been able to afford a mission to explore the massive protoplanet in such detail. But now, Dawn has gone even beyond that. Having discovered so many of Vesta’s secrets, the stalwart adventurer left it behind in 2012. No other spacecraft has ever escaped from orbit around one distant solar system object to travel to and orbit still another extraterrestrial destination. Dawn devoted another 2.5 years to reshaping and tilting its orbit even more so that now it is identical to Ceres’. Once again, that was essential to the intricate celestial choreography in March, when the behemoth reached out with its gravity and tenderly took hold of the spacecraft. They have been performing an elegant pas de deux ever since.

Dawn takes great advantage of being able to orbit its two targets by performing extensive measurements that would not be feasible with a fleeting visit at high speed. As its detailed inspection of a strange and distant world continues, we can look forward to more intriguing perspectives and exciting insights into our solar system. On its eighth anniversary of setting sail on the cosmic seas for an extraordinary voyage, the faithful ship is steadily accumulating great treasures.

Urvara Crater, Ceres

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

Urvara Crater, Ceres
Dawn observed this region inside Urvara crater on Aug. 19. The crater is about 100 miles (160 kilometers) in diameter and is named for an Indian and Iranian deity of plants and fields. Although many craters have a mountain in the center, as we explained when we saw the entire crater from three times farther away in the second mapping orbit, Urvara has an interesting ridge, visible at lower left. Full image and caption.

Dawn is 915 miles (1,470 kilometers) from Ceres. It is also 2.45 AU (228 million miles, or 367 million kilometers) from Earth, or 1,025 times as far as the moon and 2.45 times as far as the sun today. Radio signals, traveling at the universal limit of the speed of light, take 41 minutes to make the round trip.

Dr. Marc D. Rayman
4:34 a.m. PDT September 27, 2015

 
See other posts from September 2015

 

Or read more blog entries about: asteroid 4 Vesta, mission status, asteroids, Dawn, asteroid 1 Ceres

Comments:

Messy: 09/28/2015 08:32 CDT

About the picture of Occator crater, Has anyone come up with an explanation as to the considerable dimming of the rectangular area next to the center of spot 5? When it was first seen at the earliest orbits, it was as bright as the center, but now, you can barely see it and those photos were taken from much farther away then....why? Can it be evidence of volcanism?

Marc Rayman: 09/28/2015 11:02 CDT

Messy, It's notoriously difficult to make scientifically meaningful comparisons of pictures taken at different distances, because the pixelation of the earlier images can be deceptive. Individual pixels in those earlier images covered larger areas and so could lead to misleading conclusions about the distribution of light within the scene. Careful analyses that account for that (and other effects, such as different illumination and viewing angles) have yielded no evidence of a change in the brightness.

David Frankis: 09/28/2015 01:44 CDT

I saw a tweet from EPSC that the white spots in Occator are salts, as yet unidentified. It doesn't seem to have had much attention amid the umpteenth discovery of water on Mars.

Jonathan Chone: 09/29/2015 03:17 CDT

Dr. Marc, as you mentioned, Dawn will "measure the distribution of mass inside Ceres", that means Dawn will provide data about internal structure of Ceres, include its sub-surface ocean right? And we can even get some clues about its magnetic field?

ScienceNotFiction: 09/29/2015 03:48 CDT

The "salts" on Ceres are a mixture of several hydrates, silicates, anhydrates, acids and alkaline materials. We need to perform a lot of chemical experiments in order to find out the effects from combining these chemical substances at different temperature and pressure. The easiest way would be collecting a sample of the mantle liquid, but this hope is dashed when we saw the sudden sealing of those large openings. The only way to collect the mantle in future mission would be those tiny light holes. The stalactite layer may have blocked some of the surfacing materials from reaching these tiny holes. A robotic rover can lower a slag pot down to collect fresh samples.

Kartturi: 09/29/2015 05:44 CDT

Just wondering, what would be the estimate for the least amount of years to reach Pluto (and get into its orbit, because I would also like to see its other side!) with a suitable combination of chemical (i.e., the upper stage of the launch rocket) and ion propulsion, as well as any suitable gravity assists that would be available on the way there? (Could one use gravity assists also to decelerate the spacecraft?)

Messy: 09/29/2015 07:01 CDT

a suggestion: Name that mountain "Mt. Kellogg" after Dr. John Harvey Kellogg, the inventor of cornflakes. It should fit the ICC specifications (if barely).

Phenocryst: 09/29/2015 01:43 CDT

The images Dawn takes of Occator Crater from Low Altitude Mapping Orbit should be spectacular! It is obvious the white accumulations are related to fractures, likely eruptive or tectonic in origin. One question for Dr. Marc... Would or could an extended mission utilize a lower orbit than LAMO?

ScienceNotFiction: 09/30/2015 02:29 CDT

To Dr. Rayman, Congratulation to your phenomenal success of the DAWN project ! I had learned a great deal of the complexity involved in navigating DAWN in our solar system using the newest ion drive. Based on my speculative theory on possible surface electrostatic discharge event, my question is how much electrostatic discharge can DAWN take when approaching near the 375km orbit ? Would it be catastrophic ? My other question is about the tiny triangular dark patch appearing on all of the recent photos. Seems to me the damage took place during HAMO. Are you informed of the situation? What can cause such damage, gamma ray from the sun?

Marc Rayman: 09/30/2015 01:27 CDT

Jonathan: Yes, the objective of measuring the distribution of mass is to learn about the internal structure (as we did at Vesta), but the measurements will not have sufficient resolution to directly detect an ocean if it is present. Nevertheless, the data will help place constraints on the possibility of a present or past ocean. Katturi: I think of ion propulsion as a tool in the toolbox of mission designers. There have been many studies (including ones in which ion propulsion is used in the inner solar system, where sunlight is abundant, to provide the boost needed to travel quickly to the outer solar system), but there is no one simple answer to your question. Many choices, compromises, and tradeoffs need to be made in designing a mission. Phenocryst: We intend to leave Dawn in the next orbit (LAMO). I addressed your question in my August 2014 Dawn Journal (search for Omnipodawnt) in more detail than I can include here.

Marc Rayman: 09/30/2015 01:29 CDT

ScienceNotFiction: Thank you for your continuing interest and kind words. Electrostatic discharge is not a threat to the spacecraft. The camera is healthy and the pictures do not show any indications of damage. The feature you are seeing has been there all along, including in the Vesta images. (I just quickly found one random example for you: PIA14959.) As with all cameras (indeed, all scientific instruments), before quantitative scientific analysis can be productively undertaken, processing of the data needs to account for all the subtleties of the instrument performance. (Dawn performs regular, careful calibrations of the instruments to provide the necessary information.) So the feature is visible in raw data (which we call level 1a) but is absent in the first round of calibration (which we call level 1b). In some cases, in order to more quickly release cool pictures to the public, those thorough calibrations are not applied, and that's why you can see such minor features.

ScienceNotFiction: 10/03/2015 02:18 CDT

Revelation of a Half-Fallen Crystal Stalactite Exposure - PIA19907 Thanks to JPL's closer look at the crescent shape light trench of PIA19593, and just as I had expected, it is in fact a slit exposure to the mantle. Don't let the bright streaks fool your eyes. The best example I can use to explain this crater is the "stay-tab" design of a soda can. One side of the "tab" was bended in a straight crack while still connected to the surface crust (the shadow of a straight crack valley confirms this), the opposite side was declined at an angle toward the light slit similar to a "stay-tab" opening without the pull ring. This crater was not formed by asteroid impact. Based on my stalactite crust theory, this partial slit was caused by the build up of weight (giant crystals) below the surface. If you observe the light streaks, it is completely different from the normal white streaks observed on other crater walls. The crust surrounding the light crescent is very thin with smooth breakage similar to the dumbbell light holes of the Occator crater, and you can even see a little bit of slope near the cliff. The darker streaks are blurry near their tips and appear as spikes of suspending crystal columns. This giant crystal was formed underneath the crust in a hemispheric star-like configuration with many columns sticking out into the background. With the current resolution, I still cannot see clearly what looks like vines on the top side of the crater "tab" in this photo. They resemble multiple smoke lines radiating from the slit or intertwined roots suspending the half-fallen crater "tab". Further evidence suggests that this crescent slit emits UV light. Checkout the coordinates longitude 180°:210° and latitude 0°:-30° on PIA19977 (PIA19974 quadrant directly below "Nawish"), you can see blue light coming out of the cresent slit clearly. Now that we have another opening to gain access to Ceres internal mantle, a very good news to all Ceres researchers.

Sean: 10/03/2015 10:06 CDT

Hi Dr. Marc, I enjoyed your Ceres post and, of course, I'm fascinated by the Ceres curiosities. What's the current speculation on the 3 energetic particle bursts Dr. Russell called "a very unexpected observation" last week in Nantes? Ralf Jaumann from the DLR Institute of Planetary Research in Berlin-Adlershof, in a paragraph about the bursts on the DLR site said, "We did not think that there could still be activity on the surface today." Did the bursts originate of the surface or inside the body of Ceres or does Dr. Russell's solar interaction remark suggest Ceres has a very weak magnetic field? New member, hope my question doesn't reflect my newbieness. ;-)

Marc Rayman: 10/04/2015 12:48 CDT

Hi Sean, Thank you for your comment, and I'm glad you're following the mission. The energetic particles did not originate inside Ceres. Such particles would not be able to travel any significant distance through Ceres' solid material. (Even the nuclear radiation the spectrometer is designed to measure travels no more than about a meter in Ceres' uppermost material.) Nevertheless, we don't have a good explanation yet. I won't engage here in speculation. I prefer science, and this is a quantitative question that requires a physics-based quantitative answer. It will be very interesting indeed to see what this unexpected observation tells us.

ScienceNotFiction: 10/05/2015 04:54 CDT

Dr. Rayman: Thanks for your answers on the framing camera issue. Did the second identical framing camera exhibit similar issue? In fact I had also spotted a persistent black spot on the photos from MRO. As DAWN approaching LAMO, we may be able to see clearer photos at around 66m per pixel. If the framing camera has a 2048x2048 CCD pixel grid, I bet the photos would look much sharper. Wouldn't it?

Marc Rayman: 10/06/2015 11:18 CDT

ScienceNotFiction: The "issue" is simply variation in the sensitivity of pixels, and yes, the backup science camera has that. I would be surprised if any camera did not. (The spots you see are not necessarily black, although they appear that way in JPEGs. Some pixels do not respond to light as strongly as others, so they look darker. That can be corrected when the image is processed using the calibration data.) In the lowest orbit, the resolution will be about 35 meters/pixel. (I presented the resolution for each mapping orbit in my July Dawn Journal, which you can find by searching for Descendawnts.) There is an important trade-off in number of pixels, because resolution is not the exclusive attribute of importance for scientific analysis. In brief, more pixels yields better resolution. But more pixels means they must be smaller, so each one collects less light, thereby reducing the strength of the desired signal, thus increasing the effect of noise caused by various physical effects.

ScienceNotFiction: 10/09/2015 08:17 CDT

Thank you for the detail explanation of the framing camera issues. Hopefully, advance CCD manufacturing technology in the future will minimize these issues. On PIA19972, I spotted fibrous materials casting their shadows on the light reflected side of the rim very clearly. You can see strands resembling "vines" or "roots" suspending in mid air like portion of a tumbleweed half-buried in a crater. This phenomenon happens inside the "Stay-tab open-slit" crater also. This may be a direct evidence of the existence of plant life (or fossilized roots) inside Ceres. Until December, you and your team can keep your fingers crossed for being the first space mission discovering evidence of plant life beyond Earth. Another "first" for DAWN !!!

ScienceNotFiction: 10/14/2015 02:25 CDT

Basaltic volcanoes inside the Cerean mantle ? Basalt (mainly composed of MgO, CaO, SiO2 and some alkali oxides) is a common mineral found in planets, moons and asteroids of our solar system. It forms at mantle temperature-depth of 1600C-1200C. Because of its higher density (about 2.5 to 3g/cm3), pockets of molten basalt will be sandwiched at lower depth of the mantle above the MgO reaction layer. As more basalt accumulates at these areas, basaltic volcanoes will grow over time through repeated eruptions. Eventually, these tectonic style basaltic volcanoes become visible on mantle surface. They will erupt during major disturbances by external electromagnetic field on the core plasma. Since DAWN cannot map of the surface features of the internal Cerean mantle, I can only speculate at this point that these volcanoes do exist, and basalt fiber (Pele's hair) is also likely to exist. The erupting molten basalt will form wind blown fibers which may accumulate on the crystal/stalactite ceiling over time. These volcanic islands would block the light coming from the core. Another word, observation of any dim or darken patches on the mantle may indicate the positions of these slowly-drifting islands. This basalt should appear light yellowish.

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