Could Mars's collision with orbiting asteroid reactivate atmosphere?

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Matt Todd
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As I understand it, Mars has 2 asteroids in orbit. One slowly moving away from Mars, the other on an orbital collision course. Could the collision possibly be violent enough to liquify the planets mantle? If so, would Mars re-establish a magnetic field? Is there sufficient ice in the polar caps to thaw and create an atmosphere? Would a newly evolved Mars with protection for it's atmoshere in the form of a magnetic field be a possibility as a result of this impact?
 
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I don't think so. An impact sufficient to put that much energy into Mars would have to have an asteroid the size of a Dwarf planet at least I'm betting. And that's before accounting for where the actual energy from the impact goes, which probably isn't into melting the mantle.
 
Ah okay. You've been very informative today, thanks for all your help Drakkith. So a dwarf planet, something with about the mass of pluto or mercury? It sounds like the impact Earth was involved in during it's evolution. I wonder if Mars would be Earth V.2 If it had undergone a similar impact.
 
Unlikely. The two planets are very very different. Mars is much smaller and less massive and is located further from the Sun. These things affect the planet greatly. But that depends on what you mean by Earth V.2.
 
Fair call. By Earth V.2 I was just meaning a planet with water and a similar atmosphere to our own. Mars actually looks as though there was liquid movent upon the surface at some stage evidenced by the Vallis Marineris (spelling) and also geological activity (Olympus Mons) One feature it does seem to lack is a decent sized moon. I speculate that Mars, if it had undergone a massive, almost terminal impact during it's evolution, and was sent into a closer orbit of the sun, could very well be Earths twin, with it's own similar satelite in orbit. Of course, for liquid water, Mars would have to be close enough to the sun to melt the polar caps, which would interfere with Earths orbit. The other possibility being that Mars was knocked closer to Jupiter, where it's immense gravitational pull on Mars could geologically thaw the planet which would be protected from the solar wind by Jupiters magnetic field. It's all speculation on things that never happened, but I find it fascinating anyway.
 
Yes, if scaled properly, near identical scenarios would probably result in extremely similar results. Your other scenarios are...very unlikely to say the least, and result in a multitude of other issues.
 
There is also a lower limit for the mass of a planet to keep its atmosphere. If the mass of a planet is too small, the corresponding gravity is not strong enough to keep surface gases from slowly diffusing into space (due to the speed of the air molecules).