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Comment by rootbear | Hacker News Reader

I was just reading about how far out into space the ejecta from the Chicxulub impact went and it really brought home how possible it is that life from Earth migrated elsewhere, Mars being an obvious possible destination. But as one gets further out, it seems less and less likely that any life found has terrestrial origins. I am very much interested in knowing if there is any independently evolved life in the oceans of Europa or any of the other ice moons.

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Space is pretty inhospitable though. Is it possible for living organisms to survive ejection, a space journey and re-entry?

It's an open question, but there is some reason to believe that bacteria can survive a journey through space. Multicellular life would be much less likely to survive, although I'm constantly amazed at how hard it is to kill a tardigrade!

Long journey to Mars in hard vacuum and under UV radiation makes it very unlikely, but bacteria spores are very resilient to harsh conditions. I think it is still theoretically possible. There are a few papers on this.

https://www.ncbi.nlm.nih.gov/m/pubmed/11539977/

A tardigrade must first complete cryptobiosis, otherwise they are fragile[1]. Given that it takes time to enter cryptobiosis (maybe 1 hour), it is unlikely that any active tardigrade would survive a meteor impact.

Suppose a tardigrade was in complete cryptobiosis and survived a journey to the surface of Mars. Conditions would need to be favorable if it were to ever regain an active metabolic state.

[1]https://www.quora.com/What-does-it-take-to-kill-a-waterbear-...

It's called panspermia, for the curious.

> Space is pretty inhospitable

Is it? Predation, old age (wear and tear), disease (pollution) are the primary reasons that what we consider "living things" die. Space has very limited vectors of death for something like the tardigrade. To some bug dessicated hibernating in a rock, it's not too bad.

> Predation, old age (wear and tear), disease (pollution) are the primary reasons that what we consider "living things" die.

...on Earth, where the multitude of things that make space inhospitable - both objectively, like no atmosphere to protect from cosmic radiation; and subjectively, like vastly different conditions that terrestrial life hasn't evolved for - aren't an issue.

Eventually, cosmic ray damage will even get the tardigrade.

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