Contamination Conundrum

Ever since we began sending humans and spacecraft to some of our solar system’s planets and moons, we've been concerned about the possibility of cross contamination—either contaminating those heavenly bodies with earthly microbes, or returning home from the Moon, after having picked up some alien microorganisms and spreading them around our planet. We note that many kinds of earthly invasive species get transported to new locales on Earth and then subsequently overrun native species, because there is nothing to check their proliferation in their new environment.

Could alien microbes (either from Earth, transported to other bodies, or from space to here) run amok and annihilate native species? This was the plot of H.G. Wells's novel War of the Worlds, which described the impending destruction of humans, until the invading monster Martians fell prey to earthly microbes and expired. The first three NASA astronauts returning from the Moon in 1969 were quarantined for three weeks, until it seemed unlikely they had picked up some Moon bugs.

These experiences have caused NASA to become increasingly concerned about contaminating any possible life on Mars or various solar system moons, where life might be harbored. It would be tragic to discover past life on one of these bodies, only to realize later that we'd inadvertently caused it to become extinct by introducing our germs. The problem has become increasingly challenging, since we've recently found many so-called extremophiles on Earth that have been shown to be able to survive the severe conditions of space, so we now know that we may have been sending invasive bugs throughout the solar system for a few years. 

NASA is fully aware that its past sterilization techniques were far less effective than today's meticulous methods. The Viking spacecraft that landed on Mars in the 1970s were most likely carrying a few Earth microbes, because they were not disinfected as thoroughly as is done today. What is the chance that those landers planted microbes that have had nearly 50 years to multiply and flourish? We are currently conducting quite sophisticated tests on Mars by rovers, to see if life might exist (or did exist) there. Could we possibly end up discovering the presence of our own bugs that have since mutated into Martian species?

But wait: there's also the possibility that all life on Earth originated not on this planet, but on Mars (or even elsewhere). Rocks have been found in Antarctica that were long ago blasted off the surface of Mars by an asteroid impact. They floated through space and were much later captured by Earth's gravity. Some of those Martian rocks appear to have microbial life (although that's controversial) enclosed in them. If so, could Mars have contaminated our planet? Might are we all really Martian immigrants?

Like many results in science—the more we come to know, the more we are shown our ignorance. So we continue looking for life elsewhere. Will we ever find it? If we do, can we be certain it is really alien? It's sort of like the old saying, “We have met the aliens, and they are us!”