Dawn's Survey Orbit at Ceres Options

[alk3997]

Ooops, sorry. I see that I mis-spoke a bit. I didn't mean to say we were seeing active fountains, I meant we may be seeing the results of fountain-like activity in the past having emplaced very high-albedo material at S5, and very low albedo material in other places, like the "scratches" type formation that has been noted to be surrounded by dark terrain.

I was referring to the end effect of such fountain activity, not trying to say it's happening right now. Sort of hard to say how long ago something like that might have happened, though. It will help enormously when we start getting some compositional clues.

-the other Doug

I misunderstood - sorry about that.

I won't be surprised if this turns out to be the result of some type of past cryovolcanic activity. The one thing I'm having problems with is figuring out how anything that is this relatively bright remains this relatively bright while being subjected to eons of solar radiation (and other types of particle radiation). I just can't get past that yet.

Andy

[Habukaz]

I was also thinking about the coating produced by such activity. I do think it could still be active though - any spray of water could be so tenuous that Dawn's cameras would not be able to detect it under even the best of conditions. If such a spray was thick enough to be easily seen, I guess the results (ice coating) would be a lot more dramatic than the bright spots we see.

[ZLD]

If active, what about some type of water slurry cryomagma? This would flow out like lava here on Earth, down the sides of whatever formation is there, or build up into a dome if thats the case. As it cools, it would probably frost over leaving a fuzzy looking, semi-transparent film, depending on non-water particle content. Still looking through research papers on the topic but the topic of what happens after the cryomagma is out in the open, is less interesting to discuss.

[nprev]

Re the possibility of active plumes: As I recall, there was at least one terrestrial spectroscopic observation of a water vapor transient a few years back & the estimated total quantity of material was quite small, perhaps a few hundred kilograms. Presumably a surface feature erupting continuously enough to appear blurred in Dawn imagery would produce a far larger amount of water vapor over time with a correspondingly larger spectroscopic signature.

I don't know if similar observations are underway right now, but given the above it seems unlikely that we're seeing an active eruption here.

[ZLD]

Spectroscopy isn't really my area. What are the prospects of detecting a non-plume like eruption? Say, if it is coming out very slowly as an extremely viscous, ammoniated or sulphated mud.

Full disclosure: I agree that it is extremely unlikely for any activity.

[Doug M.]

Something I haven't seen discussed yet: are we seeing any evidence of volatile transport? Ceres regularly warms up to over 200 K in middle and lower latitudes, and at those temperatures water and carbon dioxide ices will have significant vapor pressure. Most volatiles at or near the surface would quickly sublimate and be lost to space, but some might accrete in cold traps -- and there might be ice not far below the surface.

So, first, is there any indication yet of subsidence or other effects that might be attributed to the sublimation of subsurface volatiles over geologic time?

And second, is there any sign yet of ice in cold traps? (We didn't find any on Vesta, but Vesta has a large axial tilt -- 27 degrees -- while Ceres has hardly any. And if surface ice can survive on the Moon and Mercury...)


Doug M.

[nprev]

ZLD, I think that the answer is the same. Any semi-liquid substance viscous at Ceres' surface temperature will have a vapor pressure, and since there's no atmosphere there should be a substantial amount of diffusion. Even lava would have volatile fractions (as you mentioned) like sulfur. Ceres is known to be water-rich, though.

Bottom line is that I think we're still seeing the effects of CCD saturation by high-albedo surface solids, not gas or vapor. Whatever that stuff is (and my bet is ice) it's WAY reflective. Gonna require even higher-resolution views to make sense of it.

[TheAnt]

Something I haven't seen discussed yet: are we seeing any evidence of volatile transport? Ceres regularly warms up to over 200 K in middle and lower latitudes, and at those temperatures water and carbon dioxide ices will have significant vapor pressure. Most volatiles at or near the surface would quickly sublimate and be lost to space, but some might accrete in cold traps -- and there might be ice not far below the surface.

Interesting question Doug, I did indeed expect a bit of sublimation, and that such might be the source of the tentative reports of water molecules and/or hydroxyl.
This could have let frost accumulate closer to the poles, in partially shadowed craters or other suitable locations.
But even in the early images we could not see anything such, and that most of Ceres comes with a very dark surface, with only dots of very bright material in very few locations. This surface material might have water incorporated just as have been found on Luna, but that it is buried a bit under the surface also keep it buried and shaded so very little ever evaporate. And that's why I now find that crystals of salts is a strong contender candidate for the bright areas we see, with the possible exception of area 5, which may be ice.

[pioneer]

I understand Dawn has a Gamma Ray and Neutron Detector and a Visible and Infrared Mapping Spectrometer to determine chemical composition. What have they told us about the bright spots on Ceres?

[Paolo]

I understand Dawn has a Gamma Ray and Neutron Detector

these two are probably not getting any meaningful signal from the surface in the present high orbit

[Sherbert]

I also think sublimation of volatiles may be involved in shaping the surface. I have been trying to explain why the bright spots all over Ceres are not covered in Ceres regolith. Either the precesses creating the bright material are very recent, or even current, or some mechanism is slowing down the recovering process.

If we assume the bright material is Water Ice or frozen brine, sublimation rates would be high, creating a significant "breeze" very close to the surface, which could be sufficient to disturb and remove dust. So if volatiles are ejected onto the surface it may take a considerable length of time for them to be recovered in dust. This image, highly upscaled and zoomed, is of the bright spots in "Spot 5".

https://www.flickr.com/photos/124013840@N06...eposted-public/

My interpretation is the largest bright area, on the left, is a sort of Ice "lava" lake sitting inside a Caldera, possibly still being refreshed from below, though highly unlikely. However, the amount of sublimated gas from such a volume of Ice, could keep the area dust free. On the right flank of this Caldera it can be seen that the mound is constructed in layers and lighter, but not bright, "lava" flows can be seen radiating from the central Caldera. Smaller eruptive sites nearby could also create the smaller blotches, they also have slightly lighter "lava" flows radiating from them. They could also be depressions or small craters filled up with fluid ejecta from the larger Cryovolcanos or "Hot Springs", "Geysers" and mud Cryovolcanos. The farthest right appears to have built a sizeable cone too. Once again the resolution is not quite good enough to be sure and a small degree of interpretive license is required. It looks to me that this is, or was, a Cryovolcanically active region. The deep crater it is situated in, suggests the thickness of the Ice crust is very thin in the bottom of the crater and the original impact may have opened a crack in the crust either temporarily or possibly it is still there. Others have traced a fault line running through the crater that appears to run up the right side of the large Caldera, although it could be interpreted as a channel carved by "hot" liquid erupting from the Cryovolcano, it has a "river" like appearance.

[Phil Stooke]

Paolo's right, GRAND gets pretty much nothing until the very lowest orbit. VIMS can get dood data now, but nothing has been announced yet.

Phil

[fredk]

Apart from this release based on observations in February:
http://photojournal.jpl.nasa.gov/catalog/PIA19316

[Sherbert]

This is interesting. Is this erosion or sedimentary layering?

https://www.flickr.com/photos/124013840@N06...eposted-public/

This is close up from this original.

http://www.nasa.gov/sites/default/files/th...a19574-1041.jpg

[eliBonora]

An anagliph of Spot5's crater (from PIA19579 and 568)