When can you kill an alien lifeform?
In the movies, the answer is usually pretty elementary: It’s OK in self-defense, especially if it inspires a rousing speech about human exceptionalism. But in the real world, the choice is neither elementary nor abstract. Many missions to neighboring worlds could, by accident or design, disrupt extraterrestrial life. Under what conditions would the loss of a few aliens—admittedly, probably microbes—be acceptable?
The range of views on this topic is diverse, fascinating, and indispensable to acknowledge as we strive to detect life on other planets. Current missions to Mars, as well as upcoming missions to the sun’s outer moons, including Jupiter’s moon Europa and Saturn’s moon Titan, could potentially encounter extraterrestrial life. “It’s a question of our priorities, whether you’re an astrobiologist or a member of the general public,” says Jayme Johnson-Schwartz, a philosopher who wrote extensively on the ethics of space exploration.
NASA’s Viking mission, which landed the first robot on Mars in 1976, had a clear answer: Yes, killing a few aliens is OK, as long as there’s scientific justification for it. The Viking landers conducted experiments on samples of Martian dirt, some soaked in nutrients, some sterilized at searing temperatures. The logic was that any hypothetical microbes that got the spa treatment would come to life, producing detectable activity, while the microbes that got burned would remain quiescent, providing control.
Let’s ignore the fact that the Viking experiment apparently detected signs of life, which is the result what remains controversial almost 50 years later. (The general consensus is that the experiment showed some engaging chemical activity, but it could be explained without invoking life.) Imagine that extraterrestrials came to Earth, captured a few people, fed one group a gourmet meal, and vaporized another, just to make sure the first group was actually alive. That would be a strange introduction to a recent species.
Of course, the thought experiment fails because microbes are generally considered expendable at the individual level in a way that sophisticated life forms like humans are not, though it’s still an engaging reflection of our values about first contact. To that end, while we can’t avoid killing a few microbes here and there—whether on Earth or potentially in space—entire ecosystems are a different story.
The Space Research Committee, an international non-governmental organization dedicated to cooperation in space exploration, prohibits any action which would pose a threat to the alien biosphere — or life on our world, for that matter. This “planetary protection” principle is intended to avoid transferring life from Earth to other worlds (forward contamination) or alien life back to Earth (backward contamination).
“During the Viking mission, special care was taken to avoid introducing any terrestrial organisms that could potentially disrupt the existing Martian biosphere,” David Grinspoon, senior scientist for astrobiology strategy at NASA Headquarters, said in an emailed response, which also included comment from Nick Benardini, NASA’s planetary protection officer.