Bitch Ph.D. is temporarily away, but loyal spouse Mr. B. has taken control and turned the site into -- a science blog! Today he's talking about the interesting issue of contaminating other planets with organisms from Earth.
Nowadays, when we send out space probes, we sterilize them. What little I know of this seems to indicate that our sterilization processes may be far from perfect. Regardless, the rationale for sterilization is sound -- whether or not life exists or has existed at the probe's destination, sending some of Earth's life to the destination would potentially muck things up beyond repair. When we fear a spacecraft might not be sterile, we purposefully destroy it while it still has fuel enough to perform a fatal maneuver, as we did with the Galileo probe to protect the potential life on Jupiter's moon Europa from earthy microbes possibly riding on the probe. These are real concerns that govern our use of current robotic space probes. Suppose we didn't worry about such things. Suppose there is life, an ecosystem, where we send a space probe. Suppose further, that some hardy bacteria or fungus stowed away on the space probe and is thereby introduced into the alien ecosystem. Chances are it will die out. However, there's a slim chance that such stowaways could find habitat, potentially altering or even destroying an existing alien ecosystem.
I suspect it's pretty unlikely that we will ever find anything worth of the name "life" on Mars or elsewhere in the Solar System, but I'm certainly no expert. If we did find anything, of course, it would be incredibly important, so I am happy to keep an open mind. (On the other hand, given the small chances, I agree with a colleague who says "It's more important to look for supersymmetry than for life on Mars.") Still, one of the absolutely fascinating recent advances in the study of life's origin has been the possible role of extraterrestrial chemistry. The classic Miller-Urey experiment demonstrated the possibility of creating amino acids by shooting sparks into a chamber designed to mimic the atmosphere of the young Earth. But apparently there's good reason to believe that the Earth's atmosphere wasn't really like that in the experiment; in particular, it had more oxygen and less reducing compounds, and nobody has been able to make amino acids by zapping an atmosphere of that type. On the other hand, conditions for synthesis of amino acids may exist in space! Interstellar clouds appear to be good places to create prebiotic organic compounds, or even proto-cells. It's perfectly plausible that these could have been brought to Earth early on by crashing comets and meteorites. If so, it's clear that the other planets would have received similar interplanetary donations of organic materials; no reason to believe that they necessarily evolved into life, but a fascinating possibility nevertheless.
