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Dawn's first orbit, including RC3, March 6, 2015- June 15, 2015
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post May 15 2015, 01:03 AM
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Just to step in with a mod opinion here: Speculation on new observations of a never-before-seen world is of course encouraged; that's half the fun! smile.gif

Please take time to review the Rules & Guidelines section, and let's keep it confined to the realm of the possible within realistic constraints. Also, please avoid rants & idee fixe's; those become very tiresome very quickly. Our intent as always is to increase the signal-to-noise ratio of the Forum, so please keep that in mind.

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John Broughton
post May 15 2015, 03:28 AM
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QUOTE (Bill Harris @ May 13 2015, 07:35 PM) *
Please, continue to discuss and speculate...

There's enough evidence in the RC3 images to make some preliminary conclusions on the unusual features we see.

MOD NOTE: No, there isn't nearly enough evidence yet to draw conclusions. Currently there is an extremely limited amount of data which may be used to formulate very tentative hypotheses which will be accepted, revised or discarded based on additional evidence and critical review. Key difference.

EDIT: To avoid misinterpretation, the gist of what I failed to convey properly in my first line follows.

I see enough evidence in the RC3 images to comment on what I believe the unusual albedo features are and speculate on how they formed.

1. The extensive grooves represent deep cracks in the crust, rather than crater chains from secondary impacts.

2. The spots are volcanic cones associated with rift valleys and fault lines, rather than craters exposing more reflective material beneath. That should become obvious to all when Survey Orbit images are released in June. The vents gradually expel cold ocean water, as a safety valve to equalise the pressure caused by expansive freezing on the underside of the ice crust. The water oozes out and freezes or falls as snow, before sublimating and leaving permanent deposits of salt behind on the surface. The mountain visible since February appears to be the largest such structure on Ceres, but is dormant or extinct judging by the dust gathering on its summit. However, the brightest spot/s could well be active and have ice close to their vents - something on Ceres is producing enough water vapour to be detectable from Earth.

3. The dark patches of chaotic terrain are also associated with fault lines. They probably represent sudden flows of rock-bearing mud, flooding out when major impacts occur elsewhere on Ceres and oscillations in ocean water pressure force some plates to gnash and grind against each other. The grooves become indistinct there because of that flooding. The southwest rim of Piazzi crater and the northeast rim of 'bright spot' crater are obvious examples of this, but there are others in the southern hemisphere we haven't seen in detail yet. I won't be surprised if all such regions have grooved terrain and volcanic cones associated with them, because they represent areas where water can most easily reach the surface.
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Steve G
post May 15 2015, 05:53 PM
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I come to this site every day and even though I have been a space enthusiest for 45+ years, I rarely make comments because of the high calibur of the regulars, I would have little to add!
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Habukaz
post May 15 2015, 06:31 PM
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Dawn will pause its ion thrusting tomorrow to take navigation pictures of Ceres per the status updates. No mention of which areas of Ceres that will likely be photographed.


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Gladstoner
post May 15 2015, 09:38 PM
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Speaking of 'fun' speculation, I'll give it a shot, with heavy emphasis on 'fun' at this point....

Some scientists have said there *may* be evidence of cryovolcanism on Ceres. If that turns out to be the case, then is it possible the darkish areas surrounding the bright spots could be plume deposits?:

Attached Image


I can't help but be reminded of these features on Triton:

Attached Image


(Some of these even have darkish material eminating from brightish spots.)

The materials and processes on Ceres would be quite different than those on Triton, though, and there would be no atmosphere on Ceres to carry the particles down wind. Extensions of a Cerean plume deposit in certain directions would likely be due to the configuration of the conduits and vents.

Again, the usual caveat: This 'theory' could very well be ejected into a plume of dust as soon as higher-res imagery comes down.
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ElkGroveDan
post May 16 2015, 01:29 PM
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QUOTE (Gladstoner @ May 15 2015, 01:38 PM) *
is it possible the darkish areas surrounding the bright spots could be plume deposits?:

That's the only explanation that I can think of based on the visible details at this resolution.

What is the direction of Ceres rotation in these images?


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jgoldader
post May 16 2015, 02:32 PM
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QUOTE (ElkGroveDan @ May 16 2015, 09:29 AM) *
That's the only explanation that I can think of based on the visible details at this resolution.

What is the direction of Ceres rotation in these images?


Triton's plumes are associated with the polar caps. There is a physical model for sublimation beneath the surface of the ice, and explosive release of gas pressure that brings up dust and such with it. There were a few active plumes and many streaks from past activity, so the geysers are a widespread phenomenon.

But the lack of polar caps or obvious surface ice deposits on Ceres would suggest (possibly require) a different mechanism. Any similarity in appearance may be coincidental. And I'm still really bothered by the contrast with essentially the entire rest of the surface, which appears rocky, with deep craters not obviously revealing high-albedo features indicative of ice deposits or ice layers. I don't recall seeing prominent "mud splats" like we see on Mars from areas where material appears to have flowed out of craters. Yet in this one place, a starkly different thing is found. The features in this crater appear to be quite different at least in appearance and size than other "bright spots" found on Ceres. If anybody has the time to do a compare/contrast, quantifying the differences, that would be very interesting. But I have grades due Monday...
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scalbers
post May 16 2015, 03:36 PM
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Just a quick clarification that Triton's plumes & deposits are often found at low latitudes on this cylindrical projection, so I'm unsure why polar caps are being mentioned. Namazu Macula shown by Gladstoner is near the equator. Is the polar cap large enough to cover the entire southern hemisphere? I had heard that solar heating could help power the geysers that would be present at lower latitudes, though if we are near the summer solstice signficant solar heating would be present at all southern latitudes.


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Gladstoner
post May 16 2015, 04:43 PM
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QUOTE (ElkGroveDan @ May 16 2015, 07:29 AM) *
What is the direction of Ceres rotation in these images?


Left to right.
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jgoldader
post May 16 2015, 07:49 PM
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QUOTE (scalbers @ May 16 2015, 11:36 AM) *
Just a quick clarification that Triton's plumes & deposits are often found at low latitudes on this cylindrical projection, so I'm unsure why polar caps are being mentioned. Namazu Macula shown by Gladstoner is near the equator. Is the polar cap large enough to cover the entire southern hemisphere? I had heard that solar heating could help power the geysers that would be present at lower latitudes, though if we are near the summer solstice signficant solar heating would be present at all southern latitudes.


I believe the area you quoted is within the polar cap, which is very widespread. Contrast that terrain with the bluer terrain above it.
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Habukaz
post May 16 2015, 08:39 PM
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It might be interesting to note that although Ceres has no visible (obvious, anyway) atmosphere in the images returned thus far, that does not necessarily mean that it does not have an atmosphere in a meaningful sense of the word.

Recently, there was published a paper about what the scientists thought could be the detection of an atmosphere on Callisto, a world that in images does not look at all like it has an atmosphere. If I understood it correctly, the presence of this atmosphere would mean that Callisto possibly could have some sort of winds. Now, we already have a detection water vapour around Ceres, meaning that the suggestion Ceres could have an 'atmosphere' (in the sense of the word in the blog post I linked to) shouldn't be that far-fetched.

That said, I suspect there is a less exotic explanation for that darker area; a feature that I have been keeping track of for quite some time now. wink.gif

In this context, too, it seems relevant to bring up the comparison with a certain crater on Mercury:




Around this crater, of course, the apparent darker area is found around all of the crater rather than just some of it. Here's a lunar crater with the asymmetry property (even complete with some bright stuff!):

Attached Image


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walfy
post May 19 2015, 08:52 AM
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Another take on the latest Ceres series, in 3D:
Attached Image

Full-res here, and slowed down a bit: https://farm9.staticflickr.com/8798/1782392...4fb7dd598_o.gif

And a full-res of the dwarf planet spinning little faster: https://farm9.staticflickr.com/8761/1766330...90077a52f_o.gif

Not sure why lighting shifts in some frames, thought I did each stepp the same. it pops out of the screen, which is how it renders when putting it together the quickest. It might be cool to have it recessed, as if peering from a spaceship window, but would take a bit more time. Such a lonely, mysterious, pretty little world! That volcano-like structure is as strange as the white spots. Enjoy these days of discovery!
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jgoldader
post May 19 2015, 11:03 AM
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QUOTE (Habukaz @ May 16 2015, 04:39 PM) *
In this context, too, it seems relevant to bring up the comparison with a certain crater on Mercury:




Around this crater, of course, the apparent darker area is found around all of the crater rather than just some of it. Here's a lunar crater with the asymmetry property (even complete with some bright stuff!):


The first image is of a crater named Sander, which has bright "hollows." From looking at the movie of bright spot 5 posted a couple of pages ago, it sure looks to me that the white patches in spot 5 are in hollows. Time will tell. In digging around, I found an interesting article discussing the discovery of the bright hollows on Mercury, including those in Sander. It contains a very high-res image of Sander as well.

http://messenger.jhuapl.edu/the_mission/pu...lewett.2013.pdf

The features in Sander may be from some sort of sublimation-related process, at least that was the speculation at the time of the article. The visual similarity between Sander and bright spot 5 is pretty striking, at fairly low resolution. I wonder if we'll ever get a shot like the high-res image of Sander in that post. But thanks for posting the Sander image, it was enough to remind me to be skeptical about whether ice has any role in spot 5. What a vexing feature!
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John Broughton
post May 19 2015, 02:38 PM
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The largely resurfaced region south of the crater with the bright spots is devoid of medium to large craters, but curiously is peppered with more small craters than older terrain.
Attached Image

Suppose mud flows carrying giant icebergs covered this area; shouldn't frozen mud quickly develop its own insulating layer of dust, but pits will be created as the relatively pure icebergs sublimate away? Maybe the outer 10km or so of the crust is made of frozen mud, with pure ice further down. That would explain why there's no evidence of ice having been exposed in larger craters and causing erosion there.
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alk3997
post May 19 2015, 03:40 PM
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QUOTE (John Broughton @ May 19 2015, 09:38 AM) *
The largely resurfaced region south of the crater with the bright spots is devoid of medium to large craters, but curiously is peppered with more small craters than older terrain.
...


Are those small craters or are they remnants of internal gas vents?

It is interesting how many "pieces" the right side bright spot has turned into. I think we've already seen an image where the main bright spot is at least two separate clumps. These could be very small and reflective mounds of material if it is impact related or very small outgassing pockets if it is an active area. Impact remnant still works for me at this resolution and doesn't require internal heating.

Andy
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