Few places are as hard for microbes to infiltrate as the clean rooms in which NASA assembles its spacecraft. Those drifting in through the air must run a gauntlet of filters. Those hitching a ride on employees find their paths barred by face masks and full-body hooded coveralls. Those that actually manage to land on a surface will find a world of famine and drought, devoid of water and nutrients. If they survive, most will be wiped off when the clean rooms’ walls, floors, and contents are assiduously and repeatedly scrubbed with alcohol-based solvents.
All this is in aid of “planetary protection”—the business of stopping Earth microbes from hitching a ride on our spacecraft and contaminating other worlds. NASA is bound to this principle by international treaty, and makes every effort to uphold it. After all, stowaway microbes from Earth could confound any attempts to find actual extraterrestrial life on other planets.
But it’s impossible to sterilize surfaces completely. Even NASA clean rooms have their own microbiomes—a common community of super-hardy species that somehow withstand the rigorous disinfection procedures. These communities are dominated by Acinetobacter bacteria, which are typically found in soil and water. While other microbes disappear during the cleaning process, Acinetobacter persists. Scientists have isolated strains from the surface of the Mars Odyssey orbiter, from the floors on which the Mars Phoenix lander was assembled, from the exterior of the International Space Station, and even from the station’s drinking water.