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| Pong |
 Posted: Wed Apr 30, 2008 2:23 am Post subject: Water astrochemistry |
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Forum Senior
Joined: 08 Apr 2008
Posts: 315
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In space, water normally forms amorphous ice, which is stable apparently - e.g. planetary rings. So sublimation and solar wind does not erode it much? Or is an icy surface constantly losing water only to have much of that same water bond again?
What about our crystalline (hex) ice, transported to space? Is it stable? Change to amorphous? On the surface or all through? |
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| Pong |
| Posted: Sat May 03, 2008 11:18 pm Post subject: |
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Forum Senior
Joined: 08 Apr 2008
Posts: 315
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Come on somebody help me here.  |
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| Ophiolite |
| Posted: Mon May 05, 2008 10:19 am Post subject: Re: Water astrochemistry |
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Forum Radioactive Isotope
Joined: 25 Jul 2005
Posts: 4029
Location: Scotland
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| Pong wrote: |
| In space, water normally forms amorphous ice, which is stable apparently - e.g. planetary rings. So sublimation and solar wind does not erode it much? Or is an icy surface constantly losing water only to have much of that same water bond again? |
This will depend entirely on context. What is the flux and frequency of radiation? What is the density of ice grains in the vicinity? What are the temperatures of those grains? etc
| Pong wrote: |
| What about our crystalline (hex) ice, transported to space? Is it stable? Change to amorphous? On the surface or all through? |
I don't see, on the face of it, why the crystalline ice should become amorphous. The crystalline form is at a lower energy level and so should be more stable.
_________________
The Universe is not only weirder than we imagine it is weirder than we can imagine. J.B.S.Haldane. |
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| Pong |
| Posted: Mon May 05, 2008 12:25 pm Post subject: Re: Water astrochemistry |
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Forum Senior
Joined: 08 Apr 2008
Posts: 315
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| Ophiolite wrote: |
| What is the flux and frequency of radiation? |
I was wondering about conditions around 1AU, and 10 (Saturn) for comparison.
| Ophiolite wrote: |
| What is the density of ice grains in the vicinity? |
In rings you mean? Rings vary widely, but here's a drawing recently published by the NASA-Cassini folks, to give you a sense:
However some rings are dense/thick enough to block practically all light. Most rings include few particles larger than 1m, the bulk being 5cm or less.
| Ophiolite wrote: |
| What are the temperatures of those grains? etc |
Rings, about 50 Kelvin. Though it'll change in the course of a "day".
An artificial satellite at 1AU, we could say 260 degrees K, for starters - i.e. water just frozen aboard ISS and dropped out the airlock.
Mercury may harbor polar ice, believe it or not. This is in pockets, where shade temperature less than 100K means ice could theoretically last billions of years - it just doesn't evaporate much. |
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