Jupiter is flinging asteroids at Earth 'like a sniper', top scientist warns

Unless you’re talking a Theia sized collision, Mars’ lack of a substantial atmosphere would mean the heat would rapidly dissipate into space. Theia was estimated to be about the size of Mars, which itself is only 1/10th the size of Earth.

https://en.wikipedia.org/wiki/Theia_(planet)

So optimally, there would be an asteroid, almost certainly from outside the solar system, about the size of Venus, which is 8/10ths the size of Earth, that would enter Jupiter orbit and break up before its fragments flew off to Mars. It might even have a catastrophic collision with one of Jupiter’s moons.

Only after that, a bunch of large comets would arrive, covering the still hot Mars with water.

Yes, it would take a while, but otherwise colonizing Mars would have no staying power.

Disclaimer: Opinions posted on Free Republic are those of the individual posters and do not necessarily represent the opinion of Free Republic or its management. All materials posted herein are protected by copyright law and the exemption for fair use of copyrighted works.