I've written before about international efforts to drill into lakes hidden underneath the ice of Antarctica. Some of these lakes may have been cut off from the outside world for more than half a million years - plenty of time for new species of bacteria to develop. A Russian team drilling into Lake Vostok has been the most recent effort to find success, and last week they announced that they had indeed found a previously-unknown species of bacteria. Exciting stuff. Except that, only days later, they've had to retract their claim amid revelations about contamination in their equipment.
Water collected from the narrow bore-hole had been sent to a laboratory for analysis, where preliminary results revealed DNA fragments only 86-percent similar to others found on Earth. A finding like that is usually taken as evidence for a new life from. A more detailed analysis later showed that a number of contaminants had combined to mimic new DNA. Of course, by then the eager scientists had already released a press release claiming their new discovery.
Although new life under the Antarctic ice sheet would be fascinating, it doesn't hold a candle to the sort of scrutiny claims of extra-terrestrial life must face. If a Mars rover or Europa lander or Titan probe were to claim discovery of the first life on another world, the proof would have to be irrefutable. Even the slightest hint of contamination by Earth bacteria would cast enough doubt on the finding that it would probably never escape continued questioning.
You might think that there's no way life from Earth could survive the radiation, extreme cold, and vacuum conditions inherent in space travel, but you'd be wrong. In what Apollo 12 astronaut Pete Conrad has called "the most significant thing we ever found on the whole...Moon," the moon-walkers found bacteria living on old landers sent years before. There, in the harshest conditions ever explored by man, we found life. Not life which evolved for those extreme environments, just unwitting Earth bacteria along for the ride.
This shocking revelation in hand, NASA has since made every effort to sterilize spacecraft which leave Earth-orbit. The Galileo probe was crashed into Jupiter to avoid contaminating Europa, and Cassini will suffer the same fate to protect Titan and Enceladus. Future exploration of moons such as Triton will surely follow this same plan. Unfortunately, the place we are searching hardest for life is also the most challenging to protect. Since the 1970s, two Viking landers, Pathfinder, Spirit, Opportunity, Phoenix, and Curiosity have touched down on the surface of Mars. Soon InSight will join them, as will Curiosity's yet-to-be-named sister. Chances are, at least one of these visitors has carried with it stowaways from Earth. With Mars' active water cycle and global winds, who knows where such creatures could end up. And, a hundred years from now, when a new species of life is discovered which bears passing similarity to some on Earth, how will we answer the question of its origin?
It's a basic fact of science that we cannot observe nature without affecting it, but how great our effects are may be up to us. I think we're doing the best that we can, but in our search for answers to the biggest questions, we will undoubtedly face our biggest challenges.