patch of surface ice in Mars crater photographed (OK not a first, but..)

[Martin]

http://news.bbc.co.uk/2/hi/science/nature/4727847.stm

 

it looks to be a round patch of ice about 10-15 kilometer in diameter

 

in the middle of a larger crater.

 

the crater is in Vastitas Borealis

 

yeah there is a lot of water ice at the poles of Mars, and maybe this is not especially surprising news, but I was glad to see the picture, so passing it along in case anyone else is interested

[Thomas Kirby]

That's not even close to a surprise. Both poles have icecaps the size of Texas. Is there supposed to be a magic dividing line on a planet that has 300 kilometer per hour winds?

[Ophiolite]

I don't think Martin was presenting it as a 'Gee, look at this' event, but rather as part of the slowly building body of evidence that water is both more common and more accessible than the popular view amongst planetologists and certainly areologists and areographers ten or even five years ago. As such it is noteworthy.

[us.2u]

As obviously Mars does contain H2o, as to how much who knows? do you know if methane exists here Ophiolite? I guess if Mars is supporting life of any degree that would be a fantastic surprise! So I indeed think Martins report like you said Ophiolite is noteworthy indeed....us.2u

[Thomas Kirby]

Millions of cubic kilometers of ice at the poles, seasonal variations in the visible size of the icecaps that correspond with the seasons, winds that blow hard enough to drive sand and dust into the middle of the icecaps, and someone is surprised to see patches of ice in craters when the dark patches are plainly visible in many craters and they follow the contours of the land.

[Thales]

Forgive my ignorance but I was under the impression that the mars polar caps where mainly frozen CO2, not water ice, which adds weight to the importance of this latest find.

[Thomas Kirby]

They officially decided that the north pole had to be water ice a long time ago. Here is a good place to start:

 

http://svs.gsfc.nasa.gov/search/Scientist/MariaZuber.html

 

 

More lengthy explanation

 

The mechanisms for preserving water in craters are pretty clear. Just set a glass of water somewhere quiet and see how long it takes for that to dry out. Water at near the freezing point has a vapor pressure of about four millibars. Water in that glass has a vapor pressure of a hundred or so millibars. The water is also protected from evaporation in still air by a layer of humid air, and that's almost too basic to have to look up. Craters that we can see plainly in photographs have walls hundreds or even thousands of feet high, so any water vapor has hundreds or thousands of feet to climb to escape.

 

Even though the atmosphere of Mars runs seven to ten millibars of pressure, 300 kph winds can pick up sand, let alone snow and chipped ice, and carry it great distances. It's not just the wind pressure, which per any speed runs about a 7th that of Earth (cube root of speed rule), it's the velocity that it drives smaller bits at. The wind will still accelerate light enough materials to its own velocity, and there is lower gravity to help make that happen. Water ice is just about the lightest material to be found and the most fragile. It's being carried to the equator, I'm quite certain.