One topic that comes up frequently in discussions of life on other planets is the question of how life got started on Earth in the first place. Did it develop here all by itself under the pressure of the energy present in sunlight, or was it dropped here by an asteroid or comet or passing piece of space rock that landed and seeded the infant Earth? No one has the answer to that question right now, and many years may pass before anyone can give a definitive answer. But simply raising that question puts us here on this little blue planet in a rather awkward position.
We Earthlings will eventually journey to other worlds. We’ve already been to the moon and no doubt left some of our germs there. That probably isn’t a terrible situation since none of our germs (bacteria, viruses, fungi and fungal spores, etc.) are likely to survive there for more than a short time. The moon is so inimical to life that a problem probably doesn’t exist. True, some bacterial and fungal spores may last for a long time, but unless they were seriously protected, the radiation from the sun likely killed everything soon after the Apollo astronauts left.
But eventually Earthlings will travel to other planets and moons, and the sterility problem may not be so straightforward. Some moons of the outer planets in our solar system are thought to possess large amounts of water, in some cases in the liquid form, which could potentially be the breeding grounds for microorganisms. In that case, an Earthling spacecraft landing there could potentially introduce Earth organisms. The spacecraft would have to be decontaminated, but I’m not so sure that total decontamination of a spacecraft, even unmanned and remotely operated spacecraft, could ever be achieved. How can you guarantee such a decontamination? How do you take a “decontaminated” spacecraft on a trip from Earth that far out into the solar system and guide it down to the surface without getting it contaminated? Decontamination would have to result not only in the killing of microorganisms, but in their total removal as well. The process of decontamination usually only kills microbial life, it doesn’t necessarily remove it. Foreign, if denatured, DNA and RNA could still be present on a spacecraft even if all the tests we usually do to check for it (viability, microscopic, PCR, etc.) come up negative. And seeding DNA in any form on a pristine planet is the most egregious form of Earthling arrogance I can think of.
Therefore, I propose that Earth-based spacecraft stay away from any moon or planet which could have water, such as Europa. Don’t seed the planet with a “decontaminated” spacecraft, however well-intentioned. One tiny microbe may be all it takes to “seed” a planet or moon. Let’s maintain the sterility of the system. Flyby missions which only take pictures and make scans are okay. The Moon and Mars are already contaminated, much to our chagrin, and should be allowed to remain the only two. We have walked on the moon, and we will walk on Mars, and may even walk on asteroids and other waterless, atmosphere-minus planets. Let’s leave it at that. I would hate to see Europa or Callisto or Titan or others pockmarked with Earth probes.