For the second part, we’d be able to do biochemical assays like mass spectrometry and discover immediately that the “alien” life was made of the same proteins as Earth life. Gene sequencing would then confirm a match to a known microbe, or at least to a family of them.
Now, we could argue that panspermia would predict that alien life in our solar system might be similar to earth’s species, but we would expect to see some radical differences, even at a cursory first look, given the total isolation of the two life systems for (presumably) billions of years. All that to say that it would probably be quite easy to discern whether a microbe is definitely earth life.
I suppose the much more bothersome scenario is finding a microbe that is ambiguously novel, and doesn't neatly fit any particular family of Earth microbes, but also isn't radically different enough to be confidently classified alien.
Like did we accidentally discover an eccentric and rare Earth microorganism that thrives in this unusual environment, or is it an honest to god extraterrestrial and life in both spheres just happens to converge along certain lines by evolutionary convenience or chemical necesssity? How would we tell?
Chemical space is very very large. Like we can say for certain that only a very tiny percentage of all possible synthesizable organic molecules have ever existed in our universe. The combinatoric explosion is just so enormous that I think its incredibly unlikely that the only configuration of molecules that supports life is our own here on Earth. In fact, I think we know this given that there are artificial amino acids that can be incorporated into our existing protein biochemistry without a problem. Thats a small example but it points to a much larger space of chemical compositions that can support life. So an entirely separate evolutionary process would almost certainly land in a very different chemistry for things like information storage and molecular machines like protein.
Also our biochemistry is compositional, it takes small building blocks and remixes and combines them to build larger structures. I suspect that this is also a necessary feature of life in general. It’s very hard, basically impossible, for natural evolution to build huge structures like proteins just by pure uniform random selection. Instead it takes small pieces randomly, then puts them together to get complex life.
Point being, its a very very path dependent process. Any small difference in the early building blocks gets exponentially magnified when evolution uses those blocks to build life. So that leads to easily detectable, drastic differences in biochemical structure. This is evident on earth in that our biochemistry has a feature called left handed chirality that seems to be a purely random accident of the very earliest steps of life. That then was transmitted to every living being on earth. There’s probably a fifty-fifty chance that extraterrestrial biology is right handed instead. Every step in evolution also probably has random accidents just like that. Our particular biochemistry is the result of a trillion coin flips. There are probably many other biochemistries that work just fine, but look way different
You’d sequence this organism. If it came from earth you could tell. People would have either sequenced it already or a distant relative species where you could compare sequence divergence and when they shared a last common ancestor. Convergent evolution might lead to similar phenotypes but the actual sequence of genes involved is only going to be similar if those genes shared an evolutionary history.
I suppose we need a one-way valve, such that information about the sample can flow to us while nothing can affect the sample. Conceptually like a Heimlich valve. Or, as a wild alternative, we could amplify the signal in some way, perhaps using sterile equipment in space, such that any Earth life would drown out in alien life and contamination would no longer pose as big an issue.
No you can sequence these organisms and see where they came from. If you brought them from earth vs if they were not from earth would be apparent in genetic analysis.
No, yet another conclusion where the headline that runs is one of the least probable explanations.
More likely: They opened it in a museum lab with a mediocre clean room that had some stuff floating around in it and ended up culturing organisms that didn't even make the trip to space.
