Curb Your Enthusiasm: Bacteria Found on the ISS are Probably From Humans, Not Aliens

Fagjun | Published 2017-12-07 05:11

Before you get excited over the news that bacteria have been found on the outside of the International Space Station (ISS), keep in mind that the microbes are likely to have come from humans.

Are the bacteria on the ISS's exterior from Earth, or from an extraterrestrial origin?



Though we’ve been waiting a very long time for confirmation that there is indeed life elsewhere in the universe other than on Earth, we still need to maintain a healthy degree of skepticism when it comes to news of alien life. Just recently, a Russian cosmonaut announced the discovery of bacteria on the outside of the ISS. “Bacteria that had not been there during the launch of the ISS module were found on the swabs,” cosmonaut Anton Shkaplerov told the news agency TASS. “So they have flown from somewhere in space and settled on the outside hull.”


However, it’s actually too early to be making claims that the bacteria have an extraterrestrial origin. Shkaplerov has also mentioned that they’ve sent the swabs to be experimented on, but details on that experiment are very thin.

Bacteria in Space

Astronauts can bring microbes to the ISS, despite their best efforts not to.



As of now, with not many details on the bacteria, it seems to be more plausible that the bacteria actually came from Earth, hitching a ride with astronauts on the ISS. In fact, an earlier news report from TASS has said that astronauts had inadvertently brought bacteria onto the ISS through their tablets and other belongings.


But can Earth’s microorganisms survive the conditions in space? Not all can, but some will fare quite well. The near-indestructible tardigrades, for example, will be able to survive space. NASA has also reported that Corynebacterium and Propionibacterium have been found in abundance on the station. Meanwhile, the bacteria that hitchhiked on the tablets apparently were able to sneak out to the exterior of the ISS and were able to brave temperatures ranging from -150 to 150 degrees Celsius.


Of course, there’s another important question that needs to be addressed. Don’t space agencies make sure that everything and everyone they send off to space is sterilized so as to avoid the bacterial contamination of objects in space? The United Nations’ 1967 Outer Space Treaty, after all, made this one of the principles of space law.


The answer is yes. However, total sterility is impossible. Thus, there are guidelines that limit microbial contamination to just 500,000 bacterial spores. Though this seems like a lot, this amount is actually miniscule.

Extraterrestrial Bacterial Life

Mars rovers are limited to having just 300,000 bacterial spores.



Keeping microbial contamination to a minimum is important to the search for extraterrestrial life, for exactly the same reason why the discovery of bacteria on the outside of the ISS is controversial. Because we know that we’re bringing terrestrial bacteria to outer space, we can’t immediately be completely sure that any bacteria found in outer space didn’t come from us.


Searching for signs of life on Mars will be complicated because of the possible contamination by Earth’s bacteria. Mars may have once had life forms, so contamination by Earth’s bacteria may make things a little more convoluted than we’d like. If our bacteria does contaminate Mars, scientists are hoping that the microbes won’t be able to survive the planet’s harsh conditions.


We’re not sure yet if extraterrestrial life has indeed been discovered, or if the bacteria on the hull of the ISS are actually from Earth. However, it’s more likely that it’s the latter.

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