Help Shape the Future of Space Exploration

Join The Planetary Society Now  arrow.png

Join our eNewsletter for updates & action alerts

    Please leave this field empty
Facebook Twitter Email RSS AddThis

Headshot of Emily Lakdawalla

LPSC 2016: So. Much. Ceres.

Posted By Emily Lakdawalla

30-03-2016 18:31 CDT

Topics: pretty pictures, asteroids, Dawn, explaining science, asteroid 1 Ceres, conference report

At last week's Lunar and Planetary Science Conference, I enjoyed a large number of talks about Ceres, which Dawn is now orbiting at an altitude of merely 385 kilometers. Several sessions worth of talks considered a wealth of new data that has been acquired since the last time I attended scientific sessions on Dawn, at lower altitudes and hence more detail. All that freshly acquired data made for talks bursting with pretty pictures and data but relatively thin on interpretation and with little coordination (yet) across data sets, which makes them a bit hard to summarize briefly. Deputy principal investigator Carol Raymond summed the situation up well at the press briefing: "Clearly, we have a lot of work to do to put together a self-consistent story among all these different data sets."

Dawn is very different from past asteroid missions. We've mostly encountered asteroids by flying quickly past each object, never to see them again. Dawn is not that kind of mission. It's been doing science at Ceres for more than a year now, beginning from a position of great distance. In discrete steps, over the course of the last year, it has journeyed closer to Ceres, getting more data at higher resolution with each incremental step closer. In a way, Dawn's single mission to Ceres encapsulates several distinct missions in the initial exploration of other worlds. From its Approach and then Survey orbits, Dawn first identified interesting spots on Ceres. From its High-Altitude Mapping Orbit (HAMO), Dawn generated global maps, in color and in three dimensions, generating a topographic base map for further studies. HAMO was at an altitude of 1470 kilometers; it began on August 17 and ended on October 23. HAMO included six mapping cycles to acquire Framing Camera images useful for developing a 3D terrain model, described here. Two of those mapping cycles (the second and fifth) included color data from the camera.

Now Dawn is in its Low-Altitude Mapping Orbit (LAMO), at an altitude of 385 kilometers, and is remapping the whole globe, but with added data from the Neutron Spectrometer. Dawn arrived in LAMO on December 16. It will remain there for the rest of its mission, which could go into early 2017 if the remaining two reaction wheels stay healthy. If one were to fail soon, Dawn would still complete its mission using only hydrazine thrusters, surviving into the beginning of August.

Each new altitude produces an even richer data set than the altitude before it. Each richer data set makes scientists go back and rewrite papers that weren't even done being written about the previous, lower-resolution global data set. I'd like to take a moment to tip my hat in respect to a science team that has to struggle to do science against the flood of newer, better data! It's a nice problem to have, though. 

Before I get in to the content of the talks, I need to set the scene. A lot of the talks focused on differences in geology and composition among different craters or other landmarks, so here's a map of Ceres with named landmarks. Unlike at Pluto, all these Ceres names are formally approved by the IAU; the science team has prioritized getting their bearings, establishing this global context and common vocabulary before proceeding into the science.

Ceres map with nomenclature as of February 2016

NASA / JPL-Caltech / UCLA / MPS / DLR / IDA / T. Roatsch / USGS

Ceres map with nomenclature as of February 2016
This map of Ceres shows the dwarf planet's surface with features that have been named as of February 2016. It is a simple cylindrical projection centered on 0 degrees east longitude. A full list of names on Ceres is available at the USGS Planetary Nomenclature Gazetteer.

A few locations showed up repeatedly in talk after talk. These included craters with bright spots or splashes like Occator, Haulani, Ikapati, and Oxo. I include amazing pictures of Occator below. They haven't released LAMO-resolution images of Haulani or Oxo yet, but you can see them as the two bright splashes on Ceres in this color view:

Color global view of Ceres: Oxo and Haulani craters

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

Color global view of Ceres: Oxo and Haulani craters
This approximately true-color image was taken at 4:13 on May 4, 2015, as Dawn was surveying Ceres in its "Rotation Characterization 3" orbit 13,642 kilometers above the surface. Oxo crater makes a small bright splash near center; Haulani is the larger one to its right. Near the bottom of the disk is the odd cone-shaped mountain, Ahuna mons.

The primary scientific goal of LAMO is to map Ceres for the first time with GRaND, Dawn's neutron spectrometer. In talks and at a press briefing last Tuesday, Tom Prettyman reported on the status of GRaND's LAMO mapping to date. The news is good so far: the instrument is working well, and they are getting results that make sense. They see an enrichment of hydrogen in the subsurface toward the poles, with the poles showing counts of slow neutrons 40% higher than near the equator. This is much more dynamic range than GRaND observed at Vesta, which had only 6% dynamic range across its surface. Overall, the early compositional information from GRaND is in line with that of carbonaceous chondrites (like CM and CI chondrites).

LAMO isn't just for neutron spectroscopy, though. Very recently, the Framing Camera completed the acquisition of a global map of Ceres from its LAMO altitude, covering the entire globe at 35 meters per pixel. This is a major accomplishment, made all the more amazing by the loss of two of Dawn's reaction wheels. In order to complete the map, Dawn mapped Ceres over two complete orbital cycles. The first map covered much of the globe, and then a second orbital cycle allowed Dawn to fill in gaps. To conserve fuel and also to maintain constant viewing geometry and illumination conditions, Dawn almost never pointed away from directly downward, patiently waiting for the right spots to appear underneath the spacecraft at the right time. A gap in imaging stubbornly remained over Occator crater and its bright spots throughout almost the entire imaging campaign; it was only filled in February, and final gaps were covered this month. Here's a fun animation showing the slow buildup of the global map.

Filling in that final gap allowed the team to finally release some spectacular images of Occator, including a high-resolution mosaic in which you can see the diverse features on the crater floor. There was also a zoom in on the region with the bright spots, colored with lower-resolution imagery acquired from the high-altitude mapping orbit. Here is the mosaic:

High-resolution mosaic of Occator crater, Ceres

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

High-resolution mosaic of Occator crater, Ceres
Occator Crater, measuring 92 kilometers across and 4 kilometers deep, contains the brightest area on Ceres. This region was the subject of intense interest throughout Dawn's mission to the dwarf planet. Dawn's close-up view, captured from its Low-Altitude Mapping Orbit at 385 kilometers above Ceres in late 2015 and early 2016, reveals a dome in a smooth-walled pit in the bright center of the crater. Numerous linear features and fractures crisscross the top and flanks of this dome. Prominent fractures also surround the dome and run through smaller, bright regions found within the crater.

Everybody loves Occator's bright spots, but they're not the only cool thing about the crater. At the conference, Paul Schenk pointed out the different sets of fractures that cut Occator's floor. Some of them are "annular" -- they form rings around the center of the crater. In fact, annular fractures are visible for quite a distance outside the crater, on its ejecta. Schenk said that these fractures within ejecta "are common on fresh craters on Ceres, but they are not seen in the Saturn system." About a third of Occator is filled with knobby or ropey fill, with "lobate flow margins." Each of those lobes represents material that squirted between topographic highs to pond in topographic lows. Schenk showed a photo of the flow Tycho crater on the Moon, which looks surprisingly similar to Occator on Ceres. So, he said, the flowey material "is probably impact melt, but we can't discount post-impact volcanism, so we need to do detailed mapping to discriminate between the two."

The high-resolution color photo of Occator's spots is probably the best thing I saw at the whole conference. Schenk shared it in his talk. Here it is. I'm not going to talk about it until you have a chance to enlarge it and enjoy it and see what you see. Go ahead, it's worth it.

Occator's brightest spots in color

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

Occator's brightest spots in color
The bright central spots near the center of Occator Crater are shown in enhanced color in this view from NASA's Dawn spacecraft. Lower resolution color data have been overlaid onto a higher resolution view. The view was produced by combining the highest resolution images of Occator obtained in February 2016 at image scales of 35 meters per pixel with color images obtained in September 2015 at image scales of 135 meters per pixel. The three images used to produce the color were taken using spectral filters centered at 438, 550 and 965 nanometers (blue, green, and near-infrared wavelengths). Dawn's close-up view reveals a dome in a smooth-walled pit in the bright center of the crater. Numerous linear features and fractures crisscross the top and flanks of this dome.

You can see more detail in this grayscale version. I'm fascinated by the spots to the east of the central bright spot, the way that the bright stuff forms a deposit around what appear to be vents, if I'm not mistaken.

Detail view of Ceres' brightest spots

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

Detail view of Ceres' brightest spots
Two frames from Dawn's Framing Camera cover the bright spot at the center of Occator crater, Ceres, as well as a field of slightly less-bright spots to its east. The images were taken from Dawn's Low-Altitude Mapping Orbit in early 2016 with a shorter exposure than most Dawn images, allowing subtle details to be discerned within Ceres' brightest spot. Each of the two square images is about 36 kilometers on a side.

Schenk pointed out that Occator's bright central spot is a topographic depression "which we'll call a central pit because it has less syllables." My eyebrows shot up when I noticed the dome in the very center of that pit. The dome is fractured across its top. That suggests that the top of the dome extended and cracked as it was lifted up -- something was rising beneath Occator's central pit to build that dome, and the very topmost crust cracked like a Snickerdoodle cookie. Schenk commented that these sorts of pits and domes are also not seen in the Saturn system, "but they are very common on Ganymede and Callisto."

Carol Raymond spent some time at the Dawn press briefing describing the same photo. Here are my notes on what she said about it (transcribed, to the best of my ability, in real time):

We see that we have a very complex structure within that central complex. There is a dome right at the center, and material has filled in the depression, but there's a lot of irregularities in the central pit wall. The subsidiary bright spots are much less bright; the difference in brightness is a factor of two, and [the subsidiary spots are] a very diffuse set. There are also a lot of fractures that run through this area here, and we see these fractures elsewhere throughout Occator. Zoom in on the central pit, with color from HAMO data, and a couple of things pop out. The central dome has a different color tone than the surrounding material, and we also see these concentric fractures that define the central pit area, and in general the distribution material is quite irregular surrounding the dome. Fractures on the dome are radial, so the fracture patterns, the difference in color and overall geomorphology are suggesting to us that this is some recent activity within this crater. The crater is not that old, but it appears that material has come up from below and been emplaced in the central pit. We are investigating when this process occurred, whether it was recent or whether the material is just different, and what process brought this material to the surface. 

Despite differences in detail, Cerean craters tend to look a lot like similar-size craters on Dione and Tethys, and very different from similar-sized craters on Vesta, Schenk said. Almost all of Vesta's craters are "deep bowls with no complex structure," while you have central peaks and polygonal and terraced craters on Ceres as you do on Saturnian moons. In terms of the shape of its craters, then, Ceres' crust behaves like the crust of icy moons, not dry rocks.

What makes up Ceres' crust? Intriguing clues are visible in fresh craters, which make bright splashes across Ceres. Whatever that bright stuff is, it's not ice (except maybe in one case -- more on that below). Ralf Jaumann reported on investigations of this bright stuff using multispectral imaging with Dawn's framing camera. A lot of Ceres' bright craters -- as well as its bright mountain Ahuna Mons -- are, spectrally speaking, blue. Spectral blueness for crater ejecta isn't particularly surprising; it's common on planetary surfaces for crater ejecta to be spectrally blue. Surfaces that have been exposed to space for a long time are reddened by space weathering, so fresher material is less red, hence, blue. In all cases, the recent, highest-resolution photos have proven that these bluish areas are much younger than redder areas. The center of Haulani, which has a weird central ridge surrounded by flow features, "looks crater-free," Jaumann said. What is this spectrally blue material? Jaumann couldn't determine whether it was compositional differences or physical differences (i.e. variations in particle size or porosity), though he favored the latter.

Jaumann found one thing particularly puzzling: that the blue stuff found in fresh crater ejecta is also found in the streaked flanks of bright Ahuna Mons. They don't seem to have released the color image he showed at the press briefing, but here's a beautiful high-resolution grayscale mosaic; just imagine the bright slopes as also being blue.

Ahuna Mons from Dawn's lowest orbit

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

Ahuna Mons from Dawn's lowest orbit
Ceres' mysterious mountain Ahuna Mons is seen in this mosaic of images from NASA's Dawn spacecraft. Dawn took these images from its low-altitude mapping orbit, 385 kilometers above the surface, in December 2015. The resolution of the component images is 35 meters per pixel. On its steepest side, this mountain is about 5 kilometers high. Its average overall height is 4 kilometers. These figures are slightly lower than what scientists estimated from Dawn's higher orbits because new data from lower orbit gave scientists a better sense of Ceres' topography. The diameter of the mountain is about 20 kilometers. Researchers do not know how the feature formed, but they believe that its formation is unrelated to the similar-sized impact crater that it sits next to.

I asked Jaumann about all the different kinds of flow features visible in and around Ceres' craters. He said:

In general, we have flow features which are related to mass wasting [e.g. landslides], flow features which are related to volcanic activity, and flow features which are related to materials which are highly volatile. We see all of them on Ceres, which makes it, in another way, unique. They are mostly related to the impacts that we have, but it's not clear which materials are flowing. We have to look at the viscosity of the material. We can distinguish with geology between wet and dry flows; dry materials can flow if they have small particle size. Anything can be mobile. We see so many flow features on such a low gravity object. That's very interesting: it means material that we have is very low-viscosity and it can flow even when there is low gravity. We need more topographic information in order to understand this. That's a processing issue. We have the data, but it needs time to nail down topographic processing on the order of 35 meters per pixel. We did this for Vesta and we can do it for Ceres. We should be able to get height resolution on the order of a third of a pixel. Once we know what the process is, we can say which material has been flowing.

Christina de Sanctis reported on early results from the Visible and Infrared Spectrometer (VIR) from LAMO. In HAMO, VIR had acquired a global map at 400 meters per pixel. In LAMO, VIR is able to see at 100 meters per pixel, but has so far imaged a relatively small amount of the globe. Globally, a combination of magnesium-bearing clays, ammonium-bearing clays, magnesium carbonates, and some unknown dark component provide a good fit to Ceres' spectral colors in VIR wavelengths. Next, she tackled the bright regions, including the posts in Occator, the ejecta of Oxo and Haulani craters, and the flanks of Ahuna Mons. She said that among them all, Ahuna stands out for the strength of the carbonate signal in the spectra, whereas Oxo is the only place where exposed surface water is detected. She repeated her contention, said at the Division for Planetary Sciences meeting in the fall, that the presence of ammonium indicated an outer solar system source for Ceres surface materials (perhaps even Ceres itself). She concluded that Ceres' surface is a mixture of different materials that result from pervasive alteration by water: "Water is key."

Kynan Hughson looked a little more closely at Oxo crater, the only one on Ceres that shows a specific detection of water. He said it wasn't necessarily in the form of ice; the water could be bound into minerals as hydrated salts. But Oxo's far northern location makes it plausible that there is near-surface ground ice affecting the crater's geology, he said. Jean-Philippe Combe examined where specific VIR pixels showing water fell on camera images: 'The ice is associated with hummocky sloped material in the crater floor as well as margins of lobate flow structures" which could possibly be "ice-cemented flows." Both Hughson and Combe reported that the Dawn team plans to observe Oxo repeatedly to see if there is any change in its ice-related features with time. They haven't released high-resolution images of Oxo in color yet, but here is a lower-resolution 3D view that I made.

Oxo: A small, bright Cerean crater in 3D

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

Oxo: A small, bright Cerean crater in 3D
A region in Ceres northern' latitudes contains a variety of craters including one small one with a very bright wall and a fainter splash of bright ejecta. North is to the right. It is a combination of two images taken on June 21 and 24, 2015, during the Survey phase of the Ceres mission. The image is about 270 kilometers wide by 240 tall. This crater has been named "Oxo."

Crossed-eye stereo

Parallel-eye stereo

Flicker gif

Simone Marchi made an intriguing observation about Ceres' craters. There are quite a lot of them; the Dawn team's map now includes 544 craters larger than 20 kilometers in diameter, and many smaller ones. For craters between 20 and 80 kilometers in diameter, Ceres is "saturated," meaning that each new crater obliterates, on average, one older crater, so that the number of craters stays constant with time. But at larger diameters, craters are missing -- there should be more craters of sizes greater than 100 kilometers than are observed. Models suggest that there should be 10 to 12 craters larger than 400 kilometers in diameter; Ceres has none. There ought to have been 180 craters larger than 100 kilometers, of which 40 would be observable today after all that battering; yet only 16 are observed.

Maybe, Marchi suggested, the big craters are just hard to spot: "let's try to squeeze the data and see if we can find something." Using the global topographic data set, he tentatively identified a few large-scale depressions; he was confident about one of them, less so about the other two. These may be the missing biggest basins, but he still can't find the mid-sized ones. Marchi explored a variety of hypotheses relating to collisional or orbital history to explain the missing mid-sized craters on Ceres, but couldn't make any of them work. "The answer for this conundrum needs to be some internal process," he said. "Internal evolution of Ceres is key to understanding its cratering record."

Some clues to Ceres' internal evolution can be found in the shapes of its craters (which are often polygonal) and in its global sets of fractures. Katharina Otto, Debra Buczkowski, and Jennifer Scully all reported on their efforts to map these features, but the work was fairly preliminary; they have made maps, but have much more work yet to do to interpret those maps and compare them with each other. Scully did report that one of Ceres' two global fracture sets has a geometry that points back to one of Marchi's basins as a possible source of the stresses that caused the fracturing. But the other set of fractures that she mapped didn't align with any obvious geological feature.

In general, the talks at LPSC continued to reinforce the conclusion, made at DPS, that Ceres' outer shell is not pure ice but rather a mixture of mostly rock and less ice. This rock-ice mixture may explain some of the interesting transitional geology found in Ceres' craters, as Paul Schenk described them. Under ordinary conditions, Ceres' crust is strong like rock. But when smashed in an impact, it behaves like ice. Impacts into this material produce flows that look like lunar impact melts, though on Ceres it would have been "more like an impact mud than an impact melt." Tim Bowling showed some geophysical modeling work in which he applied rock-like behavior for some physical conditions, and ice-like behavior for others. He was able to match the shape of Occator crater -- including its central pit -- with a model that used a rock-like strength for Ceres' crust, but where the crustal material responded to the shock waves of the impact to acoustically fluidize as ice does. The conclusion he drew is that the rocky component dominates the strength of Ceres' crust, allowing it to hold up topography; but when the crust is being stretched, the weakness of the ice allows it to be pulled apart. This work, like much of what I saw in the sessions, was preliminary, as Bowling acknowledged to chuckles from the audience: "My thinking on this has actually changed in the last 24 hours after a conversation with Gareth Collins and some hasty reanalysis."

Julie Castillo-Rogez presented some early work on the puzzle of how an ice-rich Ceres can lack a pure ice shell. If you start out with a mixture of ice and rock in a body as massive as Ceres, and melt any of the water, gravity really ought to force the rock to drop to the center and the water to float to the top, stratifying it into an ice mantle over a rocky core. As the water freezes, it even excludes salt, forming a pure ice layer at the very top, as with the icy moons of the outer solar system. But that's not what we see at Ceres. Instead, Castillo-Rogez said, we see this mixture of ice and rock, as well as spectral evidence for minerals that formed at higher pressures. Is it possible that Ceres once did have a pure ice shell, but has since lost it? She suggested that impact-induced sublimation could have caused Ceres to lose up to 50 kilometers' thickness of ice shell in 100 to 200 million years of bombardment.

All in all, three days of Ceres was a lot to swallow, and it's taken me another three days to try to absorb it all and summarize the presentations in this post. We'll continue to drown in data from Dawn for as much as another year, and then the mission will be over. I fully expect it to take decades for scientists to get everything that they can out of this rich data set.

See other posts from March 2016


Read more blog entries about: pretty pictures, asteroids, Dawn, explaining science, asteroid 1 Ceres, conference report


davidpalmer: 03/31/2016 04:11 CDT

Finally, with the lowest mapping orbit of Dawn, the bright spots of Occator Crater have been sufficiently resolved to understand their true nature. Evidently the impact that created Occator Crater punched through into a subsurface ocean of Ceres, and created a weak spot that has henceforth served as a conduit for cryovolcanic outflows. The main bright spot is inside of what appears to be a volcanic caldera, a depressed area with concentric cracks around (and inside) its perimeter, evidently produced through the collapse of the roof of a "magma" chamber after its contents were disgorged. And in the center of the caldera we have more recent dome-building (i.e., analogous to a terrestrial lava dome that forms after a previous eruption), where slush has apparently pushed up (possibly in preparation for another significant eruption in the future), and this has caused radial cracks in the center (on the slopes of the dome) where the crust has been stretched. This is extremely similar to the processes and landforms characterizing terrestrial volcanism, the only difference being that water is the "magma" in this case. And just as with terrestrial volcanoes, we have outlying "cinder cones," apparently associated with fractures pointing radially away from the central caldera (to the east of the caldera/main vent). While it might be suggested that the bright deposits involved with these features (tentatively identified as hydrated magnesium sulfate, i.e. the dessicated remains of outflowing brine) are simply a relic of ancient hydrothermal activity spawned by the heat of the original impact (approx. 80 million years ago on the basis of crater counts), the fact that the material is still bright, and not darkened by cosmic radiation and meteoric dust over tens of millions of years, indicates that much of the cryovolcanic activity has been far more recent than the formation of Occator Crater. Plus the observations of apparent vapor or fog above the floor of Occator Crater, in a diurnal cycle, indicate the same. Because unless there were geologically recent (or even currently-ongoing) outflows, any such volatiles would have sublimed away to nothing long ago. The largely-rocky crust of Ceres, I would interpret as a combination of residual solids left behind after billions of years of sublimation of the frozen water content, combined with accumulated meteoric material. The low density of Ceres indicates that an enormous quantity of water still remains inside this body (apparently both solid and liquid), although the composition of the underground ocean is likely to be more of the nature of muddy brine (rather than clear water), which is necessary to explain the abundance of (hydrated and aqueous-related but now desiccated) solids making up much of the crust (clays, carbonates, and salts). Plus, Ceres lacks enough of an internal heat source to convect and recycle crustal material like Europa and Enceladus do, which is a process that would act to carry out ongoing differentiation, with the heavier solids sinking towards the center of the body and mostly pure ice building up new crust. On the other hand, because exposed ice is unstable at Ceres' distance from the sun, if it DID undergo convective action that brought large amounts of water to the surface, Ceres would have largely dried out by now, and be a considerably smaller (and less interesting) body. The idea that Ceres still has a subsurface ocean has certainly not been universally accepted, apparently because thermodynamic models suggest that such a relatively small body would have frozen long ago. But this is operating under the assumption that the liquid water is very nearly pure, whereas in practice it is likely to have a number of dissolved antifreeze compounds (salts such as magnesium sulfate, as well as ammonia, the latter of which is indicated by the presence of ammonia-rich clays in the vicinity of the bright spots). And an ammonia and salt-saturated brine would have a freezing point as low as minus 100 degrees Celsius, which is just a few degrees above the average global surface temperature of Ceres (estimated at minus 105 Celsius). So it wouldn't take much of an internal heat source to keep such a subsurface ocean liquid since the formation of Ceres. The processes occurring in Occator Crater are similar to what I have suggested in my "artesian hydrant" model for the otherwise-inexplicable geology of Mars' Mt. Sharp. Namely that there are conduits connecting the surface of Mt. Sharp to an underground aquifer, and which are still occasionally active, and which I deem necessary to explain the relative youth of the channel and delta deposit to which Curiosity is currently headed (an aqueous-derived landform that has a relative lack of both cratering and erosional damage, and thus must be no more than approx. 100 million years old, and possibly considerably less). I would predict that Ceres will become an extremely hot target for exobiological research, with a huge push for a sample-return from Occator Crater, as any recent outflows might contain not only fossil organisms, but possible viable ones that could be revived, if an outflow were sufficiently fresh. And given the relatively small mass of Ceres, landing on it and taking off would be relatively easy with existing technology (its mass is only about 1/700 that of Mars and 1/90 that of Earth's moon). It has been speculated that life on Earth may have originally come from Ceres, as such a small body would have cooled down to the point of supporting liquid water long before Earth (or even Mars) did so. And because of its location and low escape velocity, Ceres could be expected to have undergone numerous impacts that splattered (possibly life-bearing) material towards the inner solar system. So if microbes were to be found, an analysis of their genetics might actually reveal them to be our distant ancestors! As far as the origin of the mysterious pyramid-shaped mountain (Ahuna Mons), I find it to be a bit too much of a coincidence that there is a relatively young crater of approximately the same size right next-door, and can't help but suspect that there is a connection. And I would like to suggest the following model: as the largely-water-ice crust of Ceres has continued to thicken over time (due to the internal heat source gradually running down), cracking of the crust has occurred, some of which would be polygonal in shape, and I would suggest that the crater-creating impact occurred right next to one such polygonal section, and the resultant pressure impulse in the subsurface ocean (slightly) popped that section up through the surrounding crust. And since that time, continued freezing in the subsurface ocean has pushed the polygonal section further upwards, in response to vertical pressure created by expansion of the freezing water below, and due to the fact that the cracks defining its edges (cracks which became vertical faults) de-coupled it from the surrounding crust and allowed it to move fairly independently of that crust. So this mountain is basically what is referred to as a "horst" in Earth geology, but because of the differences in crustal composition and dynamics here, there are no surrounding "grabens," and Ahuna Mons doesn't take the shape of the linear ridge that is typical of terrestrial horsts.. David Palmer

QubitsToy: 03/31/2016 08:46 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 cornucopia. 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 available to me. This is a hobby, not science, but my experience as an architect hopefully allows me to create relatively accurate models. Thank you. animation - Real Time Model

Chris Landau: 03/31/2016 08:51 CDT

Hi David I like your long thoughtful comments. I think the surface is being reshaped on a continual basis by tidal heating of the whole dwarf planet between the sun's twenty five day spin and Jupiter's 10 hour spin. This tidal spin coupling-uncoupling, cooks this dwarf planet every day. Ceres is only 1 hour faster than Jupiter in it's angular rotation of 9 hours. They try to allign, but the sun, prevents this. There is no other source for the internal heat, driving active volcanism, on this rapidly rotating oblate spheroid, that is continually reshaping a bubbling Ceres. Vesta of course with its greater rotation and higher density/viscosity than Ceres has greater relief variation, but the driving force remains the same. The reason there is more rock than ice at the surface of Ceres, is that it is being brought to the surface in magmatic type currents, much like in a boiling cauldron, on an ongoing basis, every day. Next, the lack of large craters is because the whole planet is being reshaped on a continual basis. So most of the burst bubbles are not craters from impacts, but what you get from the appearance of Vesicular Lava, only on a planetary wide scale. We have a low boiling planet, like Jupiter's moon Io, but not on steroids, just low boiling. As for Ahuna Mons, for me the jury is still out. I thought, at first this was a high viscosity steep sided volcano like Mt. Etna, Fuji or Shasta, but there are no associated, tensional fractures here in the surrounding "country rock", no polygonal fractues in the adjacent crater to indicate a pop up event. Also why have we got a steep sided volcano on a generally low viscosity planet, only at one point? That does not make any sense. Also the active streaks on its steep sides, would preclude a once off pop up event. Even if the volcano is actively erupting now, it should not be high viscosity at such a limited point. I think we all need to think a bit more. Chris Landau (geologist) March 31, 2016

QubitsToy: 03/31/2016 03:57 CDT

Davids thoughts are so realistic I trust that they will prove themselves as correct, or nearly correct. As far as Ahuna Mons I am stuck on the concept that this is a icy deposit mound formed by the nearby bright spot (spout hole) a spray of water material that has built up over the millions of years. I also think that we will witness photos from Dawn during the next perihelion showing venting and spouts.

HarbingerDawn: 04/01/2016 05:34 CDT

"They don't seem to have released the color image he showed at the press briefing, but here's a beautiful high-resolution grayscale mosaic; just imagine the bright slopes as also being blue." For those interested, I colorized that grayscale image from the recent LAMO color map that was released. There are some errors due to the different projections, but the alignment is good on the mountain itself. Link below:

HarbingerDawn: 04/01/2016 05:35 CDT

Excuse my previous post, I meant to say HAMO, not LAMO!

JohnnyMorales: 04/02/2016 02:20 CDT

The center mound looks far more like an arctic Pingo. Impacts could have melted isolated mud rich ice lenses isolated in the crust allowing water to mobilizes under the crust to form a pingo as it rapidly refroze. The sublimation of the near surface ice would draw still mobile slush to replace it with each episode providing a brief oppty for slush to reach the surface through weak spots to erupt explosively as diffuse geysers before freezing over. Each episode would leave salts behind to grow the central mound, while the satellite geysers faded away.

JohnnyMorales: 04/02/2016 03:00 CDT

As a radical explanation for Ahuna Mons, it could have been an forward langranian object sharing Ceres orbit. Over the eons its orbit would have destabilized, allowing Ceres to catch up. Thanks to Ceres weak gravity it would have been able to maintain an independent orbit around the sun and maintain intact until it was quite close enough to Ceres to transform its independent orbit around the sun into an extremely close orbit around Ceres where it behaved more like it was a much junior partner in a contact binary. This would have prevented the gravity of Ceres from suddenly and rapidly pulling it down and destroying it upon impact once Ceres gravity had overcome its independent orbit. Instead it would have slowly drifted down to the surface of Ceres like a spaceship in a controlled descent to create Ahuna Mons.

davidpalmer: 04/02/2016 04:06 CDT

Since Ahuna Mons is a flat-topped mesa where the upper surface matches the old cratered terrain of the surrounding landscape, I think it is safe to assume that it is an uplifted crustal block.

davidpalmer: 04/02/2016 04:23 CDT

Also, the texture of the flanks of Ahuna Mons closely resembles terrestrial "slickensides," which is a product of fault zones where one block of crust slides past another while under high pressure, producing a grooved texture with smooth, reflective facets. And while a similar texture (at least at the level of resolution of Dawn's photos) could be produced by landslides on the sides of a mountain, the lack of significant piles of talus material at the base of Ahuna Mons argues against that. So my conclusion is, again, that this is an uplifted crustal block. Probably serving as a sort of "pressure relief valve" as the subsurface ocean gradually froze from the top down (and it was able to function as such a local "relief valve" because it had already been decoupled from the local crust, as a result of the original polygonal cracking and because of the adjacent crater-forming impact).

jensfridthjof: 04/03/2016 12:17 CDT

A funny thing it is just this one mountain. Are there other cracks or crack systems on Ceres that give a clue of similar processes that haven't developed as far?

QubitsToy: 04/22/2016 05:07 CDT

HarbingerDawn - Are you serious? An image shown at the last conference showed a color Ahuna Mons that looked similar to your artwork? That is going to be amazing to see.

QubitsToy: 05/09/2016 03:01 CDT

Fascinated by the size of the feature I created a 3D model from all available data. You can see two animations of the model here and here: -- - also real time models are available here -

Leave a Comment:

You must be logged in to submit a comment. Log in now.

Space in Images

Pretty pictures and
awe-inspiring science.

See More

Join The Planetary Society

Let’s explore the cosmos together!

Become a Member

Connect With Us

Facebook, Twitter, YouTube and more…
Continue the conversation with our online community!