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edgewaters
2004-Nov-26, 02:40 PM
How did the ice caps form? I know that on Earth, Antartica's covering is formed primarily from precipitation of snow, whereas the Arctic cap is primarily just frozen seawater. But here, the ice accumulates at the caps only because the poles are so cold it doesn't become liquid there. If the whole planet were so cold, it would all be covered in ice. So how come the ice on Mars is not evenly distributed?

Also, why is there no liquid water at the edges of the icecaps?

harlequin
2004-Nov-26, 08:06 PM
How did the ice caps form? I know that on Earth, Antartica's covering is formed primarily from precipitation of snow, whereas the Arctic cap is primarily just frozen seawater. But here, the ice accumulates at the caps only because the poles are so cold it doesn't become liquid there. If the whole planet were so cold, it would all be covered in ice. So how come the ice on Mars is not evenly distributed?

Also, why is there no liquid water at the edges of the icecaps?

Why would there be liquid water at the edges of the icecaps? At typical pressures and temperatures that exist on Mars water goes from solid to a gas or vise versa. Most of the time for most places on Mars liquid water simply will not form. When conditions allow the formation of liquid water, it simple will not last for very long on the surface.

Also the Mars caps also have frozen carbon dioxide in addition to water. Liquid carbon dioxide will never form on Mars (or on Earth as anyone who has handled dry ice can attest to).

But in any event, water is more likely to be in its solid form where it is the coldest (the poles). Think of it as a sort of "equilibrium." Some water will be solid and some will be vapor. (Physics/chemistry folks, yes I know this is a very loose analogy...) The colder it is, the more the equilibrium favors the solid form of water. Water vapor can travel in the atmosphere and hense it should not be surprising that water ice tend to be much more pronounced where it is coldest.

patrick
2004-Nov-26, 09:14 PM
How did the ice caps form?

When Mars had liquid water/oceans it is probable that Mars had polar caps, like we have on Earth. At some stage in time water vanished, but the caps remained.

slinted
2004-Nov-26, 09:29 PM
But here, the ice accumulates at the caps only because the poles are so cold it doesn't become liquid there.

We know there is water-vapor allowable (ie. Opportunity's recent cloud shots : http://marsrovers.nasa.gov/gallery/press/opportunity/20041117a.html ) in the atmosphere, with a high relative humidity (relative being the key word, it would take very little water vapor to saturate Mars' thin atmosphere). I would think the poles would be a natural places for that vapor to accumulate, since they are significantly colder. Most of the 'ice' on the poles is carbon dioxide, so we're talking about very low temperatures. Water vapor in the atmosphere at the equator wouldn't remain gaseous if it were transported to the poles in those temperatures. The AMES research center has a "Mars General Circulation Modeling Group" which has some great info : http://www-mgcm.arc.nasa.gov/mgcm/HTML/research.html