Water Ice Confirmed!, White stuff sublimates away Options

[glennwsmith]

Whoa! I've just read an AP summary of the press conference in which it is stated that, yes, it IS ice under the thin, insulating layer of Martian dust. And I'm going to go out on a limb and agree with the exogeologists who have been surmising that this is not just a polar region phenomenon, but global, ie, Mars may have as much water. relatively speaking, as Earth, only it is locked away as ice under a relatively thin layer of Martian regolith. And thus volcanic activity can unleash the torrents of water in evidence all over the planet. And this perhaps also accounts for the "seepages" that we see in the sides of many craters. And thus it is likely as well that there are pockets -- perhaps huge pockets -- of liquid water at many, many places under the surface.

[Guest_Bobby_*]

Ice on Mars! Now you see it, now you don’t
Scientists say they know white stuff was frozen water because it vanished

http://www.msnbc.msn.com/id/25274243/

[elakdawalla]

The AP story had at least one quote that was copied verbatim from the press release; the press conference hasn't happened yet. It does contain some news from Barry Goldstein saying that they now understand the sol 22 anomaly and have developed a software patch. Glennwsmith, there probably is lots of ice underneath the surface but it is not as close to the surface elsewhere on Mars (where it is warmer) as it is near the poles.

I hope to be able to listen in to tomorrow's press conference but I've got the baby on Fridays and I don't know what her plans are for me yet...

--Emily

[deglr6328]

How do we know this is water and not CO2 ice already? We all suspect this of course but the media is reporting it as fact. TEGA hasn't found any water yet so is there some IR spectral measurement I don't know about?

[elakdawalla]

Too low pressure and high temperature for CO2 ice. We know the temperature at the landing site -- on sol 22, for instance, it was a high of -22 and a low of -80. And the pressure is very low, on the order of 8 millibars. If you look at a phase diagram for carbon dioxide, you'll see it's always a gas under all these conditions -- it has to get really, really cold to make carbon dioxide ice, and you don't get that cold at the low elevations near Mars' north pole during the summer.

I took this phase diagram from an interesting article, "Why You Can't Have a Snowball Fight on Mars"

This may make you wonder, okay, if you read that diagram it looks like water should be stable as a solid under these conditions, so why did the chunks vaporize? The problem is that the diagrams assume equilibrium conditions. But Mars is a big system and there's heating during the day and cooling at night and dry or wet air masses moving in and wind doing stuff, so at any moment things aren't in equilibrium. I understand that there could be some conditions prevailing at the Phoenix landing site that might even lead to net deposition of water ice, but they've always seemed fairly sure that excavated chunks would sublimate during the day. (I wonder if any water ice deposition happens in cold traps overnight.) Large bodies of ice like what's exposed under the lander might show little change, sublimating a tiny bit during the day and getting deposited on a bit overnight. But if you sublimate much of a chunk during the day, it's gone for good; it's not like a chunk is going to reappear from nothing overnight, so chunks that are sufficiently small should go away as a result of cyclic sublimation and deposition.

--Emily

[deglr6328]

m! case closed. forgot about the relatively high temps right now at the landing site.

[alan]

Water being stable as a solid at 8 millibars as indicated on a phase diagram would require a partial pressure of water vapor of 8 millibar not a total atmospheric pressure of 8 millibar. A layer of dirt on top of the ice could prevent the water vapor sublimated from the ice from diffusing away to the atmosphere so the vapor pressure of water vapor below the soil could remain near atmospheric pressure. Removing the dirt layer protecting it would allow the water vapor to disperse. Then the ice would then be exposed the the atmosphere which is mostly CO2 with little water vapor. Ice at the surface would be unstable and would sublimate unless the temperature was low enough to be at equilibrium with the partial pressure of water vapor in the atmosphere.

[silylene]

Not to toss out the water too soon, but ....

There is also the possibility that this loss of bright stuff in the trenches could be water of hydration evaporating from a salt newly exposed to the open dry atmosphere. (water of hydration of a salt is NOT ice.) This would change the crystal morphology of the salt. This would then be expected to change the brightness/reflectivity of the salts. Frankly, I am surprised to see that everyone is proclaiming this ice without eliminating this possibility.

For example, magnesium sulfate exists as MgSO4.7H2O. The waters of hydration are lost in a very dry atmosphere over about 3-4 days. The hydrated form is bright and crystalline and reflective. The annhydrous form is dull and non-reflective. I remember doing this experiment as a freshman in college!

I want to see analytical proof of water. I really do hope this is water !

p.s. I found this very nice paper, discussion exactly these phase transitions in mag sulfate under martian temperature/pressure conditions, and expected physical appearance: CONVERSION OF CRYSTALLINE MgSO4.XH2O TO THE HYDRATED AMORPHOUS PHASE – A
RAMAN, NIR, AND XRD STUDY. http://www.lpi.usra.edu/meetings/lpsc2006/pdf/2168.pdf

[Juramike]

Evidence of water ice now being reported on CNN:
http://www.cnn.com/2008/TECH/space/06/20/p...s.ap/index.html

(I have a minor issue with this sentence in the article: "However, an initial soil sample heated in a science instrument failed to yield evidence of water". - Couldn't they have said "did not determine evidence for water" instead of using the f-word?)

-Mike

[centsworth_II]

There is also the possibility that this loss of bright stuff in the trenches could be water of hydration evaporating from a salt newly exposed to the open dry atmosphere....This would then be expected to change the brightness/reflectivity of the salts.

Even if this could explain change in brightness of a surface, what about the entire disappearance of small, dislodged chunks?

[ElkGroveDan]

It's probably time to start looking for evidence of rust on the footpads...

[ugordan]

Yeah, Phoenix' price as used hardware might be going down. Nothing a good paint job can't fix, though!

[nprev]

Evidence of water ice now being reported on CNN:
http://www.cnn.com/2008/TECH/space/06/20/p...s.ap/index.html

CNN TV also running the story, including a sidebar with Miles O'Brien that featured an animated before & after GIF very much like those seen here...is anybody at UMSF now a credited TV star, perhaps...?

[hortonheardawho]

( briefly dropping out of lurking mode...)

As much as I hate to do so, I have to agree with silylene: the case for water-ice -- at least in the Goldilocks trench -- is "not proven".

Here is a sol 20-24 3D animation of the shadowed area in the trench.

I created it to see if I could see how much of the clumps remained after the "sublimation". Unfortunately even the NASA gif image drops out in the darkest part of the shadow -- where the most interesting clumps were. But if you look closely at the bright clumps that fade nearest the shadow edges I think you can see that the clumps do not completely disappear.

Even in the darkest shadow there appears to be "something" where the white clumps were -- so, yes, there may have been a dramatic change in the white clumps -- but perhaps no more so than the reductiion in the brightness parts of the top of the trench.

Yeah, I believe that it's water-ice but it's not yet scientifically proven.

I am still puzzled why the infrared spectrum from the left SSI camera has not been cited as supporting evidence for water-ice.

( jumping back into cyber-space...)

[chris]

I created it to see if I could see how much of the clumps remained after the "sublimation". Unfortunately even the NASA gif image drops out in the darkest part of the shadow -- where the most interesting clumps were. But if you look closely at the bright clumps that fade nearest the shadow edges I think you can see that the clumps do not completely disappear.

Also unlurking briefly....

If the lumps were dirty ice, then surely you wouldn't expect them to completely disappear.

Chris