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The Bright Spots on Ceres
David Palmer
post Mar 27 2015, 10:38 AM
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It has been suggested that the highly anomalous bright spots on Ceres represent cryovolcanic or evaporative plumes, and one of the pieces of evidence presented for this model, has been the fact that they seem to project above the rim of the crater which hosts them. However, the plume model is highly implausible, for three main reasons:

1) A plume would spread out and be diffuse, and not be concentrated in one super-bright spot.....an example would be the plumes of Enceladus, which are not even visible with the sun to the observer's back (equivalent to the orientation of Dawn when it was photographing Ceres), but rather the plumes of Enceladus are only visible when back-lit. Any plume intense enough to produce the surface brightness of the feature on Ceres, would be expected to spread out over a vast area, similar to what we see with the volcanic plumes of Jupiter's Io (which ARE visible when "fore-lit," appearing as large umbrella or parabola-shaped features rising above the limb)

2) Any plume activity vigorous enough to be visually conspicuous would result in ice crystals settling down (as "snow") on the surface, at least locally, or even globally (as is the case with Enceladus), resulting in a very high surface albedo in at least the crater hosting the bright spots. And yet there is nothing of the sort there....in general, Ceres' surface is a relatively uniform grey, even directly adjacent to the bright spots.

3) We would expect a plume to be variable, whereas the bright spot (albeit completely unresolved) was seen by Hubble years ago.....which makes the case even more strongly, to the effect that the surrounding landscape should by now have a thick layer of snow and be highly reflective, if indeed there are active plumes.

As an alternative to the plume model, I would like to propose the following hypothesis: that the bright spots represent cryovolcanic spring mounds which, due to the very low surface gravity of Ceres, have grown to enormous heights....the water flows out of a fissure but quickly freezes, and then more flows out on top of that, and more on top of that....till we end up with a gigantic stalagmite-shaped structure of highly reflective ice, which may be hundreds of meters high, even perhaps exceeding a kilometer. This formative mechanism would be rather similar to that of the black and white smokers on the ocean floor of Earth where, due to the buoyancy of the water, we see an environment that simulates a very low gravity regime, and in which vertical chimneys of precipitated minerals form (which would be unstable in a high-gravity surface environment).

If the outflow is liquid (not high-speed ice particles as in the case of Enceladus), then we do not face any of difficulties presented by a plume.....all the water (very quickly turning to ice) would stay in the immediate region of the vent. And while it would freeze quickly, over time it would also sublime at a substantial rate, which likely accounts for the thin water vapor atmosphere detected by Herschel. But because of the low gravity and relatively high temperature (up to minus 35 Celsius), and the comparative lack of atmosphere, this water vapor is quickly lost to space, and so does not coat the surrounding surface, except perhaps the small amount that manages to reach the poles.

David Palmer
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Posts in this topic
- David Palmer   The Bright Spots on Ceres   Mar 27 2015, 10:38 AM
- - nprev   Problem is, liquid water just cannot exist below a...   Mar 29 2015, 04:10 PM
- - dudley   Found both posts in this new thread interesting an...   Mar 29 2015, 08:25 PM
|- - David Palmer   Actually, and contrary to popular belief, liquid w...   Mar 30 2015, 01:25 AM
- - marsbug   Wouldn't any significant water ice on the surf...   Mar 30 2015, 08:46 AM
|- - David Palmer   QUOTE (marsbug @ Mar 30 2015, 01:46 AM) W...   Mar 30 2015, 10:18 AM
- - marsbug   Sorry, I meant by Dawn, as I recall that Herschel ...   Mar 30 2015, 02:39 PM
- - katodomo   I seem to remember that when the plumes were disco...   Mar 30 2015, 05:25 PM
- - dudley   NASA seemed to have downplayed the possibility of ...   Mar 30 2015, 06:16 PM
|- - David Palmer   QUOTE (dudley @ Mar 30 2015, 10:16 AM) NA...   Mar 30 2015, 10:15 PM
- - elakdawalla   Remember that the science team isn't monolithi...   Mar 30 2015, 10:23 PM
- - dudley   Under these circumstances, it's difficult to e...   Mar 30 2015, 11:45 PM
- - TheAnt   @David Palmer: Correct, a "spring mound...   Mar 31 2015, 03:40 AM
- - dudley   I'm not really clear on why the proposed ...   Mar 31 2015, 07:29 PM
|- - David Palmer   QUOTE (dudley @ Mar 31 2015, 11:29 AM) I...   Mar 31 2015, 08:50 PM
- - JohnVV   well we will know in a bit , once the spacecraft g...   Mar 31 2015, 08:26 PM
- - Gladstoner   As we've heard, something noteworthy was spott...   Mar 31 2015, 10:21 PM
|- - ollopa   I'd hate this thread to get embarrassingly out...   Mar 31 2015, 11:05 PM
|- - David Palmer   Reply to Gladstoner: I doubt that an extended fie...   Apr 1 2015, 05:14 AM
|- - Gladstoner   QUOTE (David Palmer @ Apr 1 2015, 12:14 A...   Apr 1 2015, 08:31 AM
|- - David Palmer   Reply to Gladstoner: you make a good point, that i...   Apr 1 2015, 12:20 PM
- - Gladstoner   Well, the "pixels" in question seem to b...   Mar 31 2015, 11:30 PM
- - Explorer1   Because they are under no obligation to do so yet....   Apr 1 2015, 05:47 AM
|- - David Palmer   QUOTE (Explorer1 @ Mar 31 2015, 10:47 PM)...   Apr 1 2015, 11:58 AM
|- - algorimancer   QUOTE (David Palmer @ Apr 1 2015, 05:58 A...   Apr 1 2015, 01:42 PM
|- - fredk   QUOTE (David Palmer @ Apr 1 2015, 12:58 P...   Apr 1 2015, 05:07 PM
- - dudley   It's been reported that thermal measurements o...   Apr 1 2015, 03:33 PM
|- - David Palmer   [quote name='dudley' date='Apr 1 2015,...   Apr 2 2015, 05:35 AM
- - Explorer1   http://www.planetary.org/blogs/guest-blogs...raph-...   Apr 1 2015, 04:05 PM
- - katodomo   QUOTE (David Palmer @ Apr 1 2015, 12:58 P...   Apr 1 2015, 04:11 PM
- - nprev   MOD MODE: Thanks to the members who have correctly...   Apr 2 2015, 04:13 AM
- - Explorer1   VIRS does those measurements. Home page here: http...   Apr 2 2015, 05:47 AM
- - dudley   It was stated that the bright spots having the sam...   Apr 2 2015, 04:28 PM
- - katodomo   As it says on that site it's pretty much a VIR...   Apr 2 2015, 04:28 PM
- - dudley   The resolution at the time of the discussed temper...   Apr 2 2015, 04:41 PM
|- - David Palmer   Based on that info, it sounds like the resolution ...   Apr 3 2015, 01:30 AM
- - dudley   The presence of a spring mound on the surface of C...   Apr 3 2015, 04:35 PM
|- - David Palmer   QUOTE (dudley @ Apr 3 2015, 08:35 AM) The...   Apr 4 2015, 08:45 AM
|- - Gerald   QUOTE (dudley @ Apr 3 2015, 05:35 PM) The...   Apr 4 2015, 11:12 PM
|- - David Palmer   QUOTE (Gerald @ Apr 4 2015, 04:12 PM) The...   Apr 6 2015, 12:01 AM
- - dudley   Most improbable things do not happen, that is, of ...   Apr 4 2015, 06:11 PM
- - dudley   Yes, the bright spots already seem oddly confined ...   Apr 5 2015, 03:39 PM
- - ngunn   The curvature of Ceres is enough to 'elevate...   Apr 6 2015, 08:57 PM
|- - elakdawalla   QUOTE (ngunn @ Apr 6 2015, 12:57 PM) The ...   Apr 6 2015, 10:18 PM
|- - David Palmer   QUOTE (elakdawalla @ Apr 6 2015, 03:18 PM...   Apr 7 2015, 10:00 AM
|- - Gerald   QUOTE (David Palmer @ Apr 7 2015, 11:00 A...   Apr 10 2015, 07:54 PM
|- - David Palmer   QUOTE (Gerald @ Apr 10 2015, 11:54 AM) In...   Apr 12 2015, 12:41 PM
|- - Gerald   QUOTE (David Palmer @ Apr 12 2015, 01:41 ...   Apr 14 2015, 05:03 PM
- - dudley   An interesting point. The surface on which the cra...   Apr 6 2015, 09:46 PM
- - dudley   According to the published schedule, Dawn should b...   Apr 10 2015, 06:19 PM
- - Habukaz   The images being downlinked now will not show the ...   Apr 10 2015, 06:26 PM
- - JohnVV   -- better here ----------------------- if the rot...   Apr 11 2015, 10:36 PM
- - JohnVV   to make matters worse the gif that was released i...   Apr 12 2015, 06:55 PM
- - Habukaz   One theory (prominent?) among the researchers is t...   Apr 13 2015, 02:26 PM
- - dudley   The newly released images use the VIR data to comp...   Apr 13 2015, 08:18 PM


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