Water Ice On Mars

cathector sends along a story from SpaceWeather.com on the discovery of water ice on Mars. "Scientists have figured out the mysterious white substance unearthed by NASA's Phoenix lander on Mars. It's frozen water. The breakthrough came last week when Phoenix's stereo camera caught the substance in the act of disappearing. Bathed in martian sunlight for four days, the white substance sublimated — i.e., it transformed from solid to gas without passing through the liquid state. This is how water behaves on Mars.... Some readers have asked, how do we know the white substance is not frozen CO2 (dry ice) instead of frozen water? Answer: Phoenix's landing site is too warm for dry ice. The average daily temperature is about -70 F while dry ice requires temperatures lower than about -109 F." The animated GIF showing the ice sublimating is pretty nice too.

Comments

Snow

[Joe Tie.]

Pardon my total ignorance of the subject, but does this mean that it might occasionally snow on mars? Or would the environment be too different to allow it?

Re:Snow

[Mr2cents]

No, martian air is way too dry to form snow. There is water in the athmosphere, but IIRC it is something like a layer 1mm thick if all the water would condense on the ground. What happens is that some of that water freezes to/in the ground if it gets cold enough.

What I learned from following the press conferences online, is that since mars doesn't have a large moon, the axis of rotation changes much more than earth does, so if it is directed towards the sun, the ice could actually melt.

Re:Snow

[MichaelSmith]

Pardon my total ignorance of the subject, but does this mean that it might occasionally snow on mars? Or would the environment be too different to allow it? The area the lander in is covered by ice during the winter so we are going to find the answer to your question quite soon.

Water sublimating

[NoobixCube]

If I remember my chemistry classes correctly (there is a high chance I don't), water would do this under lower air pressure, I think. Correct me if I'm wrong, I just thought some kind of explanation would be better than "because it's on Mars".

Re:Water sublimating

[Rob Kaper]

Is water the only material that can sublimate? If not, why should we be so sure this has to be water just because we want it to be?

How come the water is so white/clean?

[viking80]

First, I think the best evidence so far that this is water is not this picture, but the fact that the Mars Orbiter's spectrometer determined that that is was a lot of hydrogen in the ground near the poles.

That some white stuff vanishes is poor evidence. They need to get the white stuff in an oven and test it.

Let's assume it is water.
What really puzzles me is how clean the water is. It is covered with what would make a dirty mud if it ever melted together. Also on earth, you never have clean water if you have flash floods like what you see as a result of a volcanic eruption or meteroid impact. You only have clean water/ice in snow and still lakes/oceans.
This implies:
1. The ice has not melted after the dust blew over it.(A long time)
2. It used to be a lake/ocean or snow

So the purity of the ice might be a bigger discovery than the fact that it is ice there.

Re:ice on Mars is nothing new

[TennilleGuy]

Yes, water ice on Mars is nothing new. That's why they went there. They could not have another failed mission, could they? Before Phoenix there was Opportunity. Why? The NASA-funded mineralogical neophytes spent our money looking for liquid water where they saw widespread hematite...coarse grained grey hematite. Fe2O3...no water in its structure! On Earth, in the banded iron formations that are BILLIONS of years old, that is a metamorphic mineral. It did not form in liquid water! Its PRECURSOR minerals (goethite; ferrihydrite; lepidocrocite) did form in water. Using hematite as a "beacon" for liquid water would be like using anthracite coal as a beacon for a coal swamp or a piece of chinaware as a beacon for a kaolin mine. Now we have a mission that is the equivalent of finding sand in the Sahara Desert? They KNEW that there was water ice there...for years. Big deal? Unbelievable spin! If they actually find anything relevant to life on Mars one needs to inquire... Why didn't they go there in the first place? Why did they waste our money landing in a billion year old metamorphic landscape? Even the face-saving hematite "blueberries" are a joke when placed into context with the remote data used to select that landing site...platy coarse-grained hematite.

not necessarily amazing

[circletimessquare]

there's a number of geological processes that can concentrate water like this

in areas on earth where a lot of freezing and thawing occurs on earth, rocks get concentrated neatly in rings according to size, as if someone sorted them

i'm not saying this process is anything like why the ice is so pure on mars, what i am saying is that there are plenty of natural processes out there that concentrate materials in orders that, contraintuitively, seem like it took intelligent concentration, but are in fact totally natural

i won't even begin to speculate what processes on mars could do this, but i wouldn't be surprised if someone more knowledgeable than me could describe such a natural mechanism for ice purification on mars