Living bacteria have been found on the outside of the International Space Station, a Russian cosmonaut told the state news agency TASS this week.
Anton Shkaplerov, who will lead Russia's ISS crew in December, said that previous cosmonauts swabbed the station's Russian segment during spacewalks and sent the samples back to Earth. The samples came from places on the station that had accumulated fuel waste, as well as other obscure nooks and crannies. Their tests showed that the swabs held types of bacteria that were not on the module when it originally launched into orbit, Shkaplerov says.
In his interview with TASS, Shkaplerov says the bacteria "have come from outer space and settled along the external surface"—a claim that sparked some media outlets to issue frenzied reports about aliens colonizing the space station.
For now, though, details about the swabbing experiment are thin on the ground. Shkaplerov did not note whether the study has been vetted by a peer-reviewed journal, which means it's unclear exactly when and how the full experiment was conducted, or how the team avoided any contamination from much more mundane bacteria on the cosmonauts or in the Earth-bound lab. Interview requests with the Russian space agency were unanswered when this article went to press.
Rather than microbes raining down from outer space, it's much more plausible that the outside of the space station became contaminated by earthly organisms, many of which can survive in the harsh environment in orbit.
Leaving Our Mark
Up in the vacuum of space, microbes have to deal with turbulent temperatures, cosmic radiation, and ultraviolet light. But Earth is home to plenty of hardy organisms that can survive in extreme environments, like virtually indestructible tardigrades. Sometimes, researchers intentionally send terrestrial contaminants, such as E. coli and rocks covered in bacteria, into space to see how it will react.
And TASS reports that on a previous ISS mission, bacteria accidentally hitched a ride to the station on tablet PCs and other materials. Scientists sent these objects up to see how they would fare in space, and the freeriding organisms managed to infiltrate the outside of the station. They remained there for three years, braving temperatures fluctuating between -150 and 150 degrees Celsius.
These types of discoveries present concerns for scientists trying to limit the spread of human germs on other worlds.
In 1967, the UN General Assembly adopted the Outer Space Treaty, which set the framework for international space law. In addition to other principles, the treaty requires any mission sent from Earth to avoid harmful contamination of celestial bodies.
NASA in particular has set strict limits on its interplanetary contamination. Apollo astronauts were quarantined when they returned from their missions, for example, to prevent extraterrestrial germs from making their way out into the world. And almost all equipment from Earth is sterilized before it heads skyward, either with extreme heat or an alcohol bath, depending on its intended destination.
These treatments are especially important for missions sent to Mars, which may have once hosted its own life-forms, leaving fossil traces in the rusty rocks.
"If you want to find Mars life, you have to get rid of the signals of Earth life so that you can see it," NASA scientist Catharine Conley told National Geographic in September 2016. Conley heads the administration's Office of Planetary Protection, which aims to reduce contamination between the Earth and other planets.
Even so, total sterility is impossible. That's why guidelines limit the amount of microbial contamination on flight systems to 500,000 bacterial spores, which is about one tenth the amount of spores in a teaspoon of seawater. Specifically, Mars rovers are limited to 300,000 bacterial spores on their surfaces. The hope is that even if some Earth bacteria hitch a ride on the robots, they'll die off in the harsh Martian environment.
But all bets may be off when and if we manage to send humans to explore Mars, writes The Planetary Society's Emily Lakdawalla: "Once we've put humans on the surface, alive or dead, it becomes much, much harder to identify native Martian life."