Mark Kelly and his crew weren't alone on the latest Endeavour mission.
In fact, a number of microbes hitched a ride with the astronauts as part of an experiment to see if life could actually have made its way to Earth from Mars. While the Endeavour mission was just a beginning, the experiment will serve as a test run for an upcoming mission to one of Mars' moons, according to Popular Mechanics.
The experiment will test the effects of the trip on microorganisms. Bruce Betts, a project director with the Planetary Society, will be sending a similar set of organisms to Mars' moon Phobos aboard a Russian spacecraft.
From Popular Mechanics:
This trip is intended as a test of the transpermia hypothesis: that Mars may have held life billions of years ago, and that organisms could have survived the trip to Earth and seeded this planet with life. Those organisms may have invaded the Earth by traveling inside rocks that were blasted off the Martian surface by meteorites. "Whether you can populate planets from other planets is one of the more profound questions," Betts says. "It's intriguing, and it's worth understanding whether the theory is really plausible."
If there was life on Mars billions of years ago, there may be a chance it made its way to Earth.
Astoundingly enough (and as crazy as the theory may sound), the theory is actually more plausible than you may think. According to Popular Mechanics, Earth and Mars have shared million of tons rocks, and microbes can survive inside these space rocks.
The Russian mission will eventually test just how possible this movie-like situation ultimately is.
These microbes aren't the only non-human passengers onboard Endeavour however. There's also the first cephalopod in space, according to Wired.
A baby squid has been sent onboard the shuttle to test if the beneficial bacteria on the squid's body react violently to the conditions. While it's been shown that bacteria often turn more harmful in the radiation and temperatures of space, this will be the first time scientists attempt to find out if good bacteria go bad in space's harsh conditions, writes Wired.