If you've seen any movie about people on a space station who find an alien, there's one common takeaway: don't bring the alien back to Earth. It's never good.
But in a way, that's what Chinese taikonauts did when they discovered actual alien life on the Tiangong space station in 2023. Of course, by "alien life", we don't mean a giant xenomorph with an extendable jaw and head shaped like a cockroach shell. It's not that kind of alien.
But members of the Shenzhou-15 mission did, in fact, discover a new species of living bacteria never before seen on Earth.
The Shenzhou mission sent three men to the orbiting Tiangong space station for 186 days. They had multiple goals: experiments, tests, and -- most importantly -- completing the actual station's construction. It would have been a milestone mission without the discovery of alien bacteria, since it was the first time a crew already in orbit (the Shenzhou-14 taikonauts) would be replaced by a new crew. It would prove China could maintain a permanent base orbiting the Earth.
A regular part of the crew's duties included sampling microbes from the air and surfaces to ensure the environment remained safe. And staying safe up there is no small thing.
It's easy to get a false sense of security floating around an orbiting space station, but you're actually living on the edge. A single malfunction of any system can end you in horrific ways. And help is so far away, it's no help at all. You're very much alone.
If a single particle floating by punctures the station, the environment will depressurize causing death in seconds. If there's a fire, you have no way to escape the smoke and the flames. Even the balance of oxygen and CO2 in the air is tenuous -- a malfunction with the CO2 scrubber can overload the air with toxic carbon dioxide, again, instantly killing the crew.
So checking for bacteria on a regular basis, like every maintenance task on the station, was crucial. And on this particular mission, the crew found a strain among the microbial samples they didn't recognize.
The bacterium was rod-shaped and, on first glance, was identified as belonging to the Niallia group, found on Earth. But on further examination, the bacteria on Tiangong station demonstrated some astounding abilities that classified them as a new species -- and made it possible for them to survive the harsh environment.
First, they were able to form spores, a sort of protective survival mode where the bacterium develops an armored shell and shuts down most of its basic activities like eating and reproducing. In this way, they went into a dormant state, an extreme hibernation, where they "wait" for better conditions. Bacteria like this is very hard to kill. They hide as spores for years, coming back to life when you least expect it.
Second, they were able to consume gelatin as a food source, and use the nutrients from the food (carbon and nitrogen) to make biofilms, or protective coatings around them to boost their survival.
This new species also demonstrated unique abilities to handle oxidative stress and repair damage from solar radiation.
The crew recognized the new strain could benefit future space missions. We could learn from its ability to withstand the extreme environment for extended periods of time. But they also added, "whether the new strain poses a direct risk to humans remains uncertain".
This is why it's a bit disturbing the crew proceeded to freeze the samples they collected and send them to Earth for review.
Once in an Earth lab, researchers were able to confirm the bacteria was, indeed, related to the common "Niallia circulans", also a rod-shaped bacteria. It's found in soil and sewage and food. If consumed by people who are immunocompromised, it can cause sepsis - a condition where your body overreacts to an infection and attacks its own organs. If not treated quickly, the condition is lethal.
Of course, the new species of Niallia found on the space station may not have this exact effect. And scientists are eager to study its unique mutations, which may help humans better survive in space.
Where did this new species of bacteria come from? Researchers assume it evolved from a strain on Earth. It's unlikely it travelled from other, alien origins.
Either way, it's on Earth now.