MESSENGER News Thread, news, updates and discussion |
MESSENGER News Thread, news, updates and discussion |
Jan 9 2012, 04:22 PM
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#391
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Member Group: Members Posts: 259 Joined: 23-January 05 From: Seattle, WA Member No.: 156 |
On Mars, swiss cheese is caused by sublimation of nearly pure CO2 (there's probably some dust contamination) sublimating into the atmosphere due to solar heating. On Mercury, I'd guess the sublimating volatile is less pure, and the halos around the hollows are due to heavier materials being redeposited. I'd also guess that the sublimation is driven not solely by direct insolation - i.e., the whole surface gets pretty hot. That might account for the differences in morphology.
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Jan 9 2012, 10:24 PM
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#392
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Solar System Cartographer Group: Members Posts: 10146 Joined: 5-April 05 From: Canada Member No.: 227 |
-------------------- ... because the Solar System ain't gonna map itself.
Also to be found posting similar content on https://mastodon.social/@PhilStooke NOTE: everything created by me which I post on UMSF is considered to be in the public domain (NOT CC, public domain) |
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Jan 19 2012, 01:21 PM
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#393
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Member Group: Members Posts: 813 Joined: 29-December 05 From: NE Oh, USA Member No.: 627 |
WOW Phil...
I can't wait for your LPSC poster! I did not realize there are similar features on the Moon. Really fascinating! Craig |
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Jan 23 2012, 01:22 PM
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#394
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Junior Member Group: Members Posts: 61 Joined: 20-March 10 From: Western Australia Member No.: 5275 |
Yes, fantastic examples. If you didn't say Moon, I would have said 'Mars'.
Is it possible, for some sort of, for want of better words, 'soil liquefaction', without water being the liquid medium. Caused either by impact, or interior seismic activity. It's coming up to Australia Day, so here's a from me. |
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Jan 23 2012, 03:56 PM
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#395
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Solar System Cartographer Group: Members Posts: 10146 Joined: 5-April 05 From: Canada Member No.: 227 |
One idea used for the lunar examples, dating back, I think, to Peter Schulz in his classic 'Moon Morphology' book, is regolith excavation and 'liquefaction' to some extent, by the occasional release of residual volcanic gases or slowly accumulating radiogenic argon. Gas-supported regolith (liquified, if you like to call it that) might account for the sharp meniscus-like boundary on most of them, as the regolith flowed back into the hollow at the end of the eruption. This idea is mentioned in my LPSC abstract. This can work just as well on Mercury - the MESSENGER team is saying there is more volatile content than expected in Mercury. (Volatiles might include sulphur compounds rather than water).
My point here - the MESSENGER folks have said several times now that these hollows are not found on the Moon. They certainly are much more numerous on Mercury, but I believe similar features are seen on the Moon, and any explanation for Mercury ought to be at least considered for the Moon as well. And on the Moon we can explore them directly - even a GLXP team could look at one. Phil -------------------- ... because the Solar System ain't gonna map itself.
Also to be found posting similar content on https://mastodon.social/@PhilStooke NOTE: everything created by me which I post on UMSF is considered to be in the public domain (NOT CC, public domain) |
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Mar 9 2012, 04:43 PM
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#396
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Solar System Cartographer Group: Members Posts: 10146 Joined: 5-April 05 From: Canada Member No.: 227 |
The new PDS data release is reflected in an update to the Mercury Quickmap interface:
http://messenger-act.actgate.com/msgr_publ...t_quickmap.html Image search is down right now but will allow downloading of individual images. Phil -------------------- ... because the Solar System ain't gonna map itself.
Also to be found posting similar content on https://mastodon.social/@PhilStooke NOTE: everything created by me which I post on UMSF is considered to be in the public domain (NOT CC, public domain) |
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Mar 9 2012, 06:30 PM
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#397
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Senior Member Group: Members Posts: 3648 Joined: 1-October 05 From: Croatia Member No.: 523 |
Sheesh, those hollows really look creepy to me, like the planet is infected with some kind of a disease. These are presented in a sRGB display-correct fashion, without any contrast enhancements:
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Mar 9 2012, 09:48 PM
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#398
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Solar System Cartographer Group: Members Posts: 10146 Joined: 5-April 05 From: Canada Member No.: 227 |
Fantastic! Thanks.
It'll never get well if you pick it! (as they say) Phil -------------------- ... because the Solar System ain't gonna map itself.
Also to be found posting similar content on https://mastodon.social/@PhilStooke NOTE: everything created by me which I post on UMSF is considered to be in the public domain (NOT CC, public domain) |
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Mar 9 2012, 11:15 PM
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#399
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Senior Member Group: Members Posts: 3516 Joined: 4-November 05 From: North Wales Member No.: 542 |
Here's what it looks like to me. There is a layer just below the surface that easily collapses (evaporates?) at the least provocation. When could such a layer have been laid down? When Mercury had an atmosphere. Could the same apply to the Moon? Why not?
If Earth were suddenly denuded of its atmosphere would hollows form? If so, where and why? |
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Mar 10 2012, 07:46 AM
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#400
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Member Group: Members Posts: 214 Joined: 30-December 05 Member No.: 628 |
Some of those raised blobs in the crater look like the result of surface tension - something that you might see after a spill of molten metal had solidified.
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Mar 10 2012, 02:43 PM
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#401
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Junior Member Group: Members Posts: 55 Joined: 6-March 10 From: Cincinnati, OH Member No.: 5246 |
The hollows look to me like they formed from the partial sublimation of a smooth mantling material at the surface. If they are formed by sublimation, then a clue to what the mantling material consists of probably lies in Mercury's exoshere: sodium, potassium, calcium..., hum, powdered igneous rock? Particularly felsic igneous rock?
I wonder if anyone has done a lab experiment of powdered alkali-rich ingeous material (phonolites, trachytes, granites, etc.) under simulated Mercury conditions of high temperature, UV, etc.? Tom One idea used for the lunar examples, dating back, I think, to Peter Schulz in his classic 'Moon Morphology' book, is regolith excavation and 'liquefaction' to some extent, by the occasional release of residual volcanic gases or slowly accumulating radiogenic argon. Gas-supported regolith (liquified, if you like to call it that) might account for the sharp meniscus-like boundary on most of them, as the regolith flowed back into the hollow at the end of the eruption. This idea is mentioned in my LPSC abstract. This can work just as well on Mercury - the MESSENGER team is saying there is more volatile content than expected in Mercury. (Volatiles might include sulphur compounds rather than water). My point here - the MESSENGER folks have said several times now that these hollows are not found on the Moon. They certainly are much more numerous on Mercury, but I believe similar features are seen on the Moon, and any explanation for Mercury ought to be at least considered for the Moon as well. And on the Moon we can explore them directly - even a GLXP team could look at one. Phil |
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Mar 10 2012, 07:00 PM
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#402
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Senior Member Group: Members Posts: 1582 Joined: 14-October 05 From: Vermont Member No.: 530 |
Some of those raised blobs in the crater look like the result of surface tension - something that you might see after a spill of molten metal had solidified. QUOTE (schaffman) The hollows look to me like they formed from the partial sublimation of a smooth mantling material at the surface. I was thinking along the lines of glass. Maybe these are areas where a thin surface layer supercooled, and as they thermally cycle, there are areas of crystallization? A different sort of phase change than sublimation. I think gasses are far more likely to be involved, but hey, crazy ideas are fun. |
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Mar 10 2012, 09:57 PM
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#403
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Senior Member Group: Members Posts: 3516 Joined: 4-November 05 From: North Wales Member No.: 542 |
The hollows look to me like they formed from the partial sublimation of a smooth mantling material at the surface. Exactly. Mantling as in descending from above rather than rising from below. We see hollows on top of hills as well as in low spots. The place this reminds me of is Io. Volatiles such as sulphur, oxides of sulphur and others are continuously mantling that world. If Mercury experienced an Io-like episode followed by a settling of rocky dust perhaps that could provide the circumstances for the hollows to form, under the very non-Io-like conditions that prevail on Mercury. |
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Mar 11 2012, 04:49 AM
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#404
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Solar System Cartographer Group: Members Posts: 10146 Joined: 5-April 05 From: Canada Member No.: 227 |
Looking back at the Quickmap interface mentioned above... you can now turn on a layer of high resolution mosaics. They appear as white boxes when zoomed out, and the detail appears as you zoom past a certain level.
Phil -------------------- ... because the Solar System ain't gonna map itself.
Also to be found posting similar content on https://mastodon.social/@PhilStooke NOTE: everything created by me which I post on UMSF is considered to be in the public domain (NOT CC, public domain) |
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Mar 11 2012, 10:52 AM
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#405
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Junior Member Group: Members Posts: 55 Joined: 6-March 10 From: Cincinnati, OH Member No.: 5246 |
I was thinking along the lines of glass. Maybe these are areas where a thin surface layer supercooled, and as they thermally cycle, there are areas of crystallization? A different sort of phase change than sublimation. I think gasses are far more likely to be involved, but hey, crazy ideas are fun. Wow. I hadn't thought of glass. That's interesting. Perhaps some type of devolatilization of impact melt sheets? I was originally thinking of fine-grained crater ejecta, but since glass is largely amorphous, it probably melts or gives off volatiles more easily than crystaline silicates. Just a guess. Yes, crazy ideas are fun. Tom |
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