The Aftermath of a Large Comet Impact on Mars

[Straw_Cat]

Suppose a large, 'dirty snowball' comet, 25-50km in diameter or more, were to hit Mars at some speed, say 75,000 km/h.
I am quite certain it would vapourize on impact. And the impact will create super-heated high-velocity shock waves which will travel around Mars at least once, probably several times.
What I want to know, is what happens then?
Especially, how long will the steam condense, and rain fall?

 

[Drakkith]

I'm not sure if the Martian atmosphere can support steam condensing and rainfall like ours does. It is only about 0.6% as dense as Earths is and its composition is very different, with CO2 making up 95% by volume.

 

[Straw_Cat]

It would be nice to be able to talk someone into doing computer modelling of this, just to see what might happen. I have run this through my mind a number of times, and I can picture the superheated steam spreading out quite rapidly: even if there isn't much of an atmosphere, at some point it will have cooled down enough to condense and cause rain or snow. The atmosphere on Mars can be quite dusty, and probably more so if a supersonic storm is created by the impact. Moisture would then condense on the relatively cold dust particles, leading to rain. It is possible even the rain would travel at what we would consider supersonic speeds, and have quite an impact when it fell.
All this has been a 'thought experiment'.

A lot of the steam from the impact would blow back into space, of course.

 

[Drakkith]

Hmmm. I wonder if it would snow or rain...according to the Wiki article liquid water cannot exist on Mars due to it's very small atmospheric pressure. I wonder if this keeps water from forming extended ice crystals as well.

 

[Straw_Cat]

"...according to the Wiki article liquid water cannot exist on Mars due to it's very small atmospheric pressure. I wonder if this keeps water from forming extended ice crystals as well."

Hard to say, without experiment with a near vacuum chamber in the dead of winter or with the proper refrigeration equipment, but one argument against this supposition in Wiki is the fact that large balls of ice do form in the vacuum of space...those 'dirty snowball' comets are proof of that. So a thin atmosphere and relatively low gravity shouldn't be a barrier to condensation. And there is now known to be water on the moon.
Come to think of it, a lot of the water on Earth is thought to have arrived from outer space over the eons, too.
:-) That includes the water in our bodies, along with everything else. We truly are star-born. :-)

 

[Straw_Cat]

We are pretty sure now that Mars once held liquid water, and for quite a while, judging by the erosion we can see on all the photos sent home. It might be that the larger, faster impacts created strong enough shock waves to blow the atmosphere into space, along with all those Martian meteorites found on Earth which scientists love to examine.
As the atmosphere got thinner, especially with the lighter gravity, the planet would have freeze-dried... frozen water would have sublimed, that is, gone from a solid to a gas without entering the liquid stage.
(This is the mechanics behind vacuum freeze-dried foods, etc. Freeze the coffee or w.h.y., then hit it with a strong enough vacuum, and the water is sucked up. This is also the recommended treatment for water damaged books and other paper items, something a book owner, an maybe someone with family photographs, might keep in mind. If these get wet in a flood, place them in baggies, and put them in a deep freeze ASAP. With a vacuum chamber and a vacuum pump, one can freeze-dry them and avoid mold damage.)
Anyhow, I posted the question in the hopes it might find its way to someone who ~can~ do a computer model of this hypothesis. I don't have the programming skills to even begin something like this. Nor can I afford to rent a Cray super-computer for a few hours or days... :-(

 

[Drakkith]

Actually I just read that the water in the polar ice caps can be swept up when CO2 sublimates and generates wind, forming clouds. I guess it is possible!

 

[Straw_Cat]

Actually I just read that the water in the polar ice caps can be swept up when CO2 sublimates and generates wind, forming clouds. I guess it is possible!

Interesting! I hadn't come across that info before. Thanks.