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Posted by: Webscientist Sep 26 2009, 08:21 AM

I've always been surprised to hear that the moon is a dead world with no water at all on its surface.
Now, the recent finding of water radically changes our approach of the moon.
If there is water in the soil, that implies that water has the ability to infiltrate into the dusty soil of the moon instead of vanishing into outerspace.
You see what I mean!
The prospect of a network of caves carved by liquid water beneath the surface of the moon can be envisaged.
You may find a similar pressure to that of the Earth at sea level about 30 meters beneath surface level on the Moon.
What are the thermal conditions at this depth? Can water appear in its liquid form?...

Posted by: Zvezdichko Sep 26 2009, 08:46 AM

No. This is what I think based on existing data.

Posted by: nprev Sep 26 2009, 09:59 AM

Sorry, but I would call that unlikely to the point of impossibility. Even a pond-sized, very localized underground aquifier would produce a global water signature many orders of magnitude greater than that observed due to transpiration through bedrock cracks & the loose regolith and subsequent diffusion through what passes for the lunar atmosphere.

Transient lunar phenomena (TLP) have been documented occasionally over the years, and some (esp. in the Aristarchus region) do seem to be related to gas emissions, the rest probably being meteor impacts. However, the only spectrum (hastily!) obtained for a TLP reportedly did not show H2O or OH.

Posted by: Juramike Sep 26 2009, 11:51 AM

Hmmm. Not sure I can agree with that statement. If I understand correctly, there are very large underground deposits of ice on Mars that have not been observed spectroscopically through bedrock cracks and loose regolith. That is why the crater impacts were required to expose the ice on Mars.


But getting back to the Moon, it could be a pure diffuse surface absorption onto the rock/dust grains. The H2O molecules deposit onto the outer few microns of the dust and is held there as a "solid". Any diffusion (not using the word percolation) in the soil column would be through sublimation-diffusion-redeposition onto deeper dust grains in the surface. I don't think there would ever be anything remotely resembling liquid flow (not even during or after an impact.)

Could it concentrate in an underground cold trap? Maybe. Then you could get a subsurface ice deposit. But it would likely be diffusing in and filling in the spaces of the dust grains to make a frozen dirt clod.

(Could the frozen dirt clod eventually deform plasticly and flow? That I don't know. That's where the total amount that exists is important. There just might not be enough H2O to do such a localized concentration.)

-Mike

Posted by: centsworth_II Sep 26 2009, 05:08 PM

With the very low water background on the Moon it would be much easier to see even a small transient signal.

Posted by: nprev Sep 26 2009, 07:31 PM

Mike, just to be clear I was thinking about the detectability of an underground liquid reservoir as postulated in the first post. Could be wrong, but it seems to me that such a thing would be emitting water vapor like crazy even via diffusion through many meters of soil, so I sincerely doubt that any exist.

Subsurface ice, now....wouldn't that be nice?

Posted by: Webscientist Oct 30 2010, 01:08 PM

The latest news regarding the evidence of subsurface water where the rover "Spirit" is trapped provides intriguing information upon the properties of water compounds on the planetary bodies where the atmosphere is very thin (Mars) or quasi non-existent (Moon).http://www.astrobio.net/pressrelease/3663/trapped-rover-finds-evidence-of-water-on-mars
I've always been surprised by the quasi-absence of water on the Moon. Now, one clearly realizes that significant amounts of water may be present in the "underground" on Mars and on the Moon.
In what shape (solid, liquid)? If present, does it sculpt caves like on Earth?

Posted by: Phil Stooke Oct 30 2010, 06:30 PM

The paper on concentrations of salts in soil on Mars should give the clue that this will not work on the Moon. There is, as far as we can see now, no evidence in samples or orbital chemical data of solution of salts from one place and deposition in another. That's the proof that water on the Moon is not behaving as it does on Earth or Mars. Caves eroded by flowing water are out of the question. The recent findings are very different from active aquifers and masses of ground ice. Even at the poles the ice is not active in the landscape as it is on Mars.

Phil

Posted by: marsbug Oct 31 2010, 09:48 PM

Lunar water is present only in regions of incredible cold. As a rule I can't imagine subsurface regions that would accumulate water being warm enough for it to melt.

I can imagine liquid water forming in the subsurface as a very rare and short lived event, for example if a subsurface volatile resevoir were close enough to a major impact to be warmed above freezing without being totally driven off or disrupted. But this would be more like a short lived pond of subsurface slurry, and would either quickly re-freze or, if there was enough impact heat to keep the subsurface warm over a longer period, be driven from the regolith as vapour.

There have been studies of impact induced hydrothermalism on Mars I believe- perhaps these might provide some further insight? There may be enough similarities for the two situations to be meanigfully compared.

Even if it transpires that impact induced hydrothermalism could work on the moon such events are likely to be rare in its history and therefore it is unlikely that such a body of water would be currently present.