The Bright Spots on Ceres |
The Bright Spots on Ceres |
Mar 27 2015, 10:38 AM
Post
#1
|
|
Junior Member Group: Members Posts: 33 Joined: 16-June 14 From: Sweet Home, Oregon Member No.: 7202 |
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 |
|
|
Apr 1 2015, 05:47 AM
Post
#2
|
|
Senior Member Group: Members Posts: 2082 Joined: 13-February 10 From: Ontario Member No.: 5221 |
Because they are under no obligation to do so yet.
Maybe after Opnav 6 finds out the ground truth they'll be shown? Otherwise it would just be more speculation.... |
|
|
Apr 1 2015, 11:58 AM
Post
#3
|
|
Junior Member Group: Members Posts: 33 Joined: 16-June 14 From: Sweet Home, Oregon Member No.: 7202 |
Because they are under no obligation to do so yet. Maybe after Opnav 6 finds out the ground truth they'll be shown? Otherwise it would just be more speculation.... If it were a private enterprise, that could be the case, but because it is taxpayer funded, it seems to me that they have an obligation to immediately release everything (and if they don't, it just fuels conspiracy-type theories, to the effect that they're trying to hide something). With the Mars rover Curiosity, all raw photos are quickly released on a dedicated website, and I don't know why things should be any different with Dawn. |
|
|
Apr 1 2015, 01:42 PM
Post
#4
|
|
Member Group: Members Posts: 656 Joined: 20-April 05 From: League City, Texas Member No.: 285 |
...because it is taxpayer funded, it seems to me that they have an obligation to immediately release everything... Unfortunately for us, that happens not to be the case. Certainly not "immediately"... they have a schedule when imagery will be moved into a public archive, and it is months as opposed to minutes. For a broader perspective, I work (as a statistician) in medical research. Public release of raw data almost never happens in this field, only partially because of patient confidentiality issues. Even raw lab data is rarely released. The product is publications of summaries & interpretations of the data. Sadly, this is associated with a bias where results which displease someone tend not to be published, whether because the results conflict with what has been previously published (potentially embarrassing) or because no statistical or practical significance was found (difficult to find journals interested in publishing). From this perspective, I'm absolutely amazed and pleased with the imagery releases by the planetary science community -- which is not to say that I would not enjoy greater openness even more. |
|
|
Lo-Fi Version | Time is now: 29th April 2024 - 12:58 PM |
RULES AND GUIDELINES Please read the Forum Rules and Guidelines before posting. IMAGE COPYRIGHT |
OPINIONS AND MODERATION Opinions expressed on UnmannedSpaceflight.com are those of the individual posters and do not necessarily reflect the opinions of UnmannedSpaceflight.com or The Planetary Society. The all-volunteer UnmannedSpaceflight.com moderation team is wholly independent of The Planetary Society. The Planetary Society has no influence over decisions made by the UnmannedSpaceflight.com moderators. |
SUPPORT THE FORUM Unmannedspaceflight.com is funded by the Planetary Society. Please consider supporting our work and many other projects by donating to the Society or becoming a member. |