Warning: the word “might” will appear a lot in today’s post.
When the Curiosity rover left Earth, it might have been contaminated with several different strains of Earthly bacteria. This was a big oops for NASA, especially for NASA’s Office of Planetary Protection, which is supposed to make sure we don’t spread our germs to other planets.
But how bad could the damage really be? Curiosity was headed for Mars. It’s not like Mars has water.
Then we found out Mars does have water. Droplets and trickles of water. Modestly sized puddles of the stuff. Now, even though Curiosity is currently located near actively trickling water, the rover is not allowed to go investigate. It might contaminate the water. It might endanger any ecosystem that might exist in the slightly damp Martian soil.
I wrote previously that we should take the risk anyway. Let Curiosity approach the water. Let Curiosity take a sample. Let Curiosity be curious. What are the odds that microorganisms from cushy, life-friendly Earth could survive on Mars? What are the odds that they could outcompete native life forms that are perfectly adapted to the harsh Martian environment?
That’s how I felt, until last week when I learned about bacterial conjugation.
According to the panspermia hypothesis, life on Earth and Mars might (there’s that word again) share a common ancestor. If so, Martian microbes might be genetically compatible with bacteria from Earth. Through bacterial conjugation, they might be able to share DNA.
They might.
Or they might not.
Finding out that bacteria on Earth and Mars are genetically compatible would be a huge discovery, assuming we knew it was happening. But Curiosity is not equipped to test for that sort of thing. Curiosity isn’t equipped to study biological activity of any kind. So the rover’s presence in and around Martian water flows might trigger changes to the local ecosystem without our knowledge.
So grudgingly, I’ll agree. Let’s keep Curiosity away from the Martian wetlands. It might not worth the risk.
Planet Pailly 
Hmmm. After billions of years of separate evolution, it seems unlikely that Earth and Mars microbes could share DNA. But I agree that, like “might”, “unlikely” probably isn’t good enough. Anyway, if we do share a common ancestor, that’s probably enough for Earth microbes to see Mars microbes as food and gorge like starved tigers let loose in a rabbit colony.
The other issue is if Curiosity is contaminated, and spreads its contamination to any water it was studying, it would make any subsequent detection of biological activity suspect.
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Your last point is becoming my biggest concern. I’d be really bummed out if we get false positives for life on Mars.
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