Dawn's Survey Orbit at Ceres Options

[dvandorn]

I imagine that impacts onto an ice world (or an icy-rocky-slush world) generate internal heating from acoustic/seismic energy propagating through the body. As we can see, there have been a lot of large impacts on Ceres. so there has been at least localized heating capable of melting ice, at least for a time. I'm not saying that a peppering of impacts could keep the core continuously warm -- I'm just saying that, when it gets really whacked and a big crater or basin is formed, I bet that anything from very localized to larger-area heating occurs. Chaos being what it is, I can imagine pockets of water melting out inside the crust from such large impacts, refreezing, and then getting exhumed by later impact and tectonic forces.

This could mean that Ceres may have been dead, for all intents and purposes, for billions of years, but that a good, solid whack could make it wheeze and burp a bit, even now.

I think when we get a better feel for the compositions of the various texture/albedo/color units, it will tell us a lot more about the possible histories of this curious little world.

-the other Doug

[Gerald]

Thinking at pockets of water:
The core of Ceres is probably still warm by radioactive decay heat of long-lived isotopes.
"If" the interior is sufficiently warm sufficiently close to the surface, there might have been or still may exist a subsurface ocean.
In this case a large impactor could have penetrated or at least have crushed the maybe 30 km icy surface crust and released some of the liquid of the presumed "mantle" ocean, in some remote analogy to a once suggested origin of the mare on our moon, besides a melt-up by kinetic impact energy.
Particularly for a large (say a few km diameter) iron-nickel meteorite it shouldn't be too difficult to penetrate the much less dense crust material of Ceres.

[ZLD]

New images up on Photojournal.

In order left to right: original crop, light decon, darkened w/ decon.



The smallest spots appear to be resolved but also really fuzzy still? Whats up with that?

Strange effect at bottom edge of large spot as well. Sorta looks like CCD bloom but I don't know that I've ever seen a situation where it was so small and also right next to another bloom, without them both merging. And here, we have 4 of them...

Just to throw an idea out there: Impact at a location with near surface water, creating the typical central peak in the crater but with an increase localized heating and pressure in the subsurface water. Water ejects through the peak in a one time eruption, blowing out the side like Mt. St. Helens, scattering salty-icy debris to the right. Sublimation has left the salts behind to slowly decay. Doesn't solve for why we don't see other larger chunks nearby though.

[alphasam]

Gonna take a stab and say they're looking like mini versions of the big pyramid/mountain thingy.

[fredk]

What's nice about the new view is that it appears to be a shorter exposure than PIA19568 (but with similar resolution). So in much of the area that was overexposed we can now see detail. Here's a direct comparison with PIA19568:

(All I've done is both frames 2x oversampled and PIA19568 rotated to match PIA19579. Some relative geometrical distortion between the two frames remains.)

The "fuzziness" around the two brightest spots on the right side is clearly real (rather than psf), since much smaller details are resolved elsewhere in the frame. The main bright spot is still overexposed in the centre (at least on the public tifs). It seems to me that we'd need considerably better resolution to understand what's going on here...

[Gladstoner]

Also today, the big mountain is nicely displayed in profile:



http://photojournal.jpl.nasa.gov/catalog/PIA19578

[Gladstoner]

In another image released today (I hope 3-image releases are daily from this point forward.... ), a handful of fracture bundles can be seen:



1. The main bundle.
2. Bundle that seems to be associated with dark-albedo material.
3. Another bundle.
4. Bundle on basin wall.
5. Faint hint of bundles that connect 1 and 3.

A couple other interesting features:

A. A shallow valley seems to merge with a scarp.
B. Some material seems to 'slop' into a relatively fresh crater.

http://photojournal.jpl.nasa.gov/catalog/PIA19577

[ZLD]

Can't say with certainty, but it looks like there another long bundle below '4' and above the crater pair, just out of resolution and incidence. Also, there's another at the far right, that would appear to connect to '3' but has been disconnected by an impact, also very faint.

[alk3997]

this thing is way too small and there is no "jupiter" to tug at it

it has been a solid bit of ice and rock for a VERY long time
and has been DEEP COLD for a very long time

impacts on "high ice " content are VERY different than on a rock or on nickel /iron

you get very FLAT floors on the impacts in ices

Yes, I agree that at those temperatures ice is harder than rock. Ceres surface today looks old to me, so I don't believe there are any active flows going on right now.

However, subsurface there are other factors that *could* be working to make water slush (or water), which could then get exposed by high kinetic energy impacts. As Gerald said long lived radioactive isotopes can provide some heat. While tidal heating isn't possible, the pressures under the crust can provide pockets of heating. Throw in some speculated salts and now the freezing point of the liquid is a little lower. Then add in heat transfer from a high energy object impacting and there could be enough heat for a water flow to occur with a large high velocity impact.

As for how the flow would look, I would expect a wave-like feature that freezes rather quickly. Maybe something like the southern rim of this crater? (Provided by user eliBonora)
https://www.flickr.com/photos/lunexit/18344202083/

All that said, I'm willing to wait for the detailed gravity measurements to see if there is a possibility that Ceres still has anything liquid in its interior.

Andy

[Gladstoner]

A comparison of craters:



The shape of the main bright spot seems to be similar to the form of the central pit in the other crater. Colored arrows point to possibly similar topographic features. Blue arrows mark high points. Yellow marks breaches in the pit walls. These features (superficially) remind me of the 'capes' and 'bays' of Victoria Crater on Mars.

[Sherbert]

I would guess the left of the two basins is newer. (Gladstone's previous post.) It has resulted from an impact on the edge of the older basin and is considerably deeper. The crust has been pushed down by the later impact, fracturing the surface and enabling the flow of dust on inclined surfaces.

This is more a conjecture. The left basin has steep terraced sides to the south, but far less well defined rims in its northern half. If the impact was at the edge of the ancient ocean and the totally frozen/rocky Southern polar "continent", the southern crater wall would appear as a normal stepped terrace, the northern crater wall collapsed and less well defined. Also the pressure of the impact would force liquid away from the impact site in the ocean below, allowing the crust to collapse. This collapse would stop at the shore line of the subsurface solid "continent" and indeed such a shore line can be made out and the bowl shape of the collapsed crust made out in an semi circle around the northern crater rim. The centre of the crater appears to be almost dead on the shore line and there is half a central peak, its northern face is missing, either via collapse or sublimation.

It is also particularly clear that North of the shore line the surface is way more smooth and shows very few deep impacts, clear signs of resurfacing and linear scarring indicating expansion/contraction or movement of the surface crust. The darker areas of the poles indicates older less recycled surface. There may not be a dust cycle as dramatic as on 67P, the gravity on Ceres prevents sublimating gases moving dust very far, but where volatile ices are near to the surface, dust will move and resurface the comet. I would suggest this is happening on a very small scale now, but in the past when the crust was thinner and in areas where the crust has been thinned or penetrated by impacts, the movement of dust by sublimating gases would have been significant enough to resurface the comet on a local level. It could be that at a low level this is what is keeping some areas of exposed ice/salt exposed, the subsurface sublimating gases escaping at the surface preventing dust settling to recover the exposed areas. Once all the volatiles are exhausted the surface becomes covered in dust. If the volatiles are being replaced by more from below, say in a very deep crater or fissure, the dust could be held at bay for a significant length of time.

Following on from that, how many of the craters on Ceres are impact craters and how many sublimation derived features such as those on 67P? An explosion of pressurised, sublimated gases within the crust could leave craters similar to Spot 1 for instance, the ejecta being the unexposed ice of the crust dispersed by the explosion. It might prove interesting to compare the craters with those left by underground atomic bomb tests. The suggestion of Spot 5 being a central mountain that blew off one of its sides, like Mt St. Helens, seems another example. Ceres is dark and absorbs a lot of sunlight, that heat must travel into the crust and have consequences, such as creating pockets of sublimated gas. Even if an impact does not penetrate to the liquid below it exposes these pockets and increases the possibility of the pressure within resulting in the explosive creation of features on the surface. The strange mountain could be another example, a small high energy impact penetrating a large "magma" chamber of volatile gases, perhaps added to by fluid under pressure escaping from the ocean below.

The coming week's pictures may suggest a whole different scenario, so this is just little more than a thought experiment to ferment ideas. We are dealing with a surface crust made largely of Water Ice, most especially, I would suggest, in the equatorial and mid latitudes. The ocean may well not ever have developed in polar regions and the surface there maybe largely made of refractory materials, rock and organics. The shrivelled and shrunken appearance of the surface we see today suggests to me that there are no longer large volumes of Water blow the crust, if any, but there may still be lakes and small seas where the energy of past impacts has locally delayed the slow freeze.

[Habukaz]

The fuzziness of the of the bright spots to the right makes me think of cryovolcanic vents spewing out a thin spray of water.



Though I guess them being miniature versions of e.g. the bright crater we saw earlier is still a good explanation.

[dvandorn]

If you're right, Habukaz, then this makes two different sets of features that resemble cryovolcanic versions of fire fountains. At region 5, here, very bright effluent has been emplaced, while in other areas, near the scratch-like wrinkle features, dark material seems to have been emplaced.

I wonder if the same processes are generating both types of features, the difference being the specific type of "lava" being generated. I know that, on the Moon, differences in the lavas feeding the various fire fountains generated glasses ranging in color from green to red to black -- could different cryo-lava constituents determine whether you get a high-albedo unit emplaced vs. a low-albedo unit?

-the other Doug

[alk3997]

But, what about the side view image that Gladstoner uplinked on page 2?

http://www.unmannedspaceflight.com/index.p...st&id=36162

Shouldn't we see something resembling relief, if not a fountain, in this image?

I'm not saying I understand the bright spots, but I still have doubts over an active vent/cryovolcanism.

Andy

[dvandorn]

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