Some bacteria have been found surviving on the outside of the International Space Station. Tardigrades are an even hardier form of microbe that can supposedly survive even close to absolute zero. They can essentially go dormant in a state very, very near death, then bounce back if and when they find themselves in suitable conditions later on. There is even speculation that life on Earth could have arrived from space in a form like this, and/or life forms originating on Earth could be living on other planets right now.
Space dust collisions as a planetary escape mechanism (In press Astrobiology, 2017)
Hypervelocity space dust is a unique entity in planetary systems like our Solar System, which is able to go past and enter the atmosphere of planets, collect samples of those planets and deposit samples of other planets. The entire system of fast space dust in a planetary system thus contains the atoms, molecules and possibly even microbial life, from all the planets and provides a means to mix them up amongst the different planets. For collecting atoms and molecules that form atmospheres, the mechanism proposed in this paper is fairly straightforward. For collecting life and life related molecules this mechanism has interesting features, but many detailed issues would still need to be studied. The violent collisions involved in this mechanism could make it difficult for life to remain intact. There are several possible collision scenarios that would all need to be explored to get a definitive answer to this problem. But even if life itself does not remain intact, it could still permit the complex molecules associated with life to get propelled into space, and that is also interesting for the panspermia process. Since space dust is ubiquitous all over the Solar System and is believed to exist in interstellar and probably intergalactic space, the mechanism proposed in this paper for propelling small particles into space could provide a universal mechanism both for the exchange of the atomic and molecular constituents between distant planetary atmospheres and for initiating the first step of the panspermia process.
According to Wikipedia, panspermia is “the hypothesis that life exists throughout the Universe, distributed by meteoroids, asteroids, comets, planetoids, and also by spacecraft in the form of unintended contamination by microorganisms.”
Of course there is still the Fermi Paradox – if life is so common, why haven’t we been able to find any evidence of it, anywhere, even once? There are ethical implications of all this. We would like to perpetuate our human species and current form of civilization, of course, and that means getting into space eventually. But if we don’t manage to pull that off, and all life on Earth is wiped out for one reason or another, panspermia means that life exists elsewhere, and somewhere, sometime, intelligent life will evolve again if it hasn’t already. But if there is absolutely no life anywhere else in the universe, the loss of it on Earth would mean the end of all life forever. That would be too heavy a burden to bear, and would mean we have a strong ethical obligation to get some self-sustaining human colonies out into space as an insurance policy. But there could be a cheaper form of insurance policy – intentionally contaminate space and nearby planets with hardy germs from Earth, and in a few billion years something will survive and evolve, somewhere, into something. Do this enough and again, eventually you will have intelligent life somewhere. But finally, if it turns out there is life on other nearby planets, even very primitive life, then intentionally contaminating them with our germs would not seem like such an ethical thing to do after all.