In a recent interview with Russian News Service TASS, cosmonaut Anton Shkaplerov discussed the presence of microbes that were found on the outside of the hull of the International Space Station, that were not present after the launch of the ISS’s modules. According to Shkaplerov, "it turns out that somehow these swabs reveal bacteria that were absent during the launch of the ISS module."
"That is, they have come from outer space and settled along the external surface."
While many news outlets interpreted "from outer space" as meaning "extraterrestrial", Shkaplerov was simply referring to the vicinity around the station: the ISS orbits at an altitude of about 400 kilometers (250 miles), and the boundary where outer space begins is defined as being at 100 kilometers (62 miles, or 330,000 feet) above sea level. Adding to this, microbes can be found as high as 77 km (48 miles) — basically, it is assumed that while these microbes were found in space, they are still considered to be very terrestrial.
But Russia’s space agency, Roscosmos, isn’t ruling out the possibility of the ISS picking up microbes from other planets. Although the experiments being conducted, simply called "TEST" and "BIORISK", are primarily meant to study how Earthly microbes proliferate and affect the structure and proper functioning of spacecraft, officials are keeping an eye on the experiment for alien bugs.
"The micrometeorites and comet dust that settle on the ISS surface may contain biogenic substance of extra-terrestrial origin in its natural form," according to a Roscosmos statement made last May. "The ISS surface is possibly a unique and easily available collector and keeper of comet substance and, possibly, of biomaterial of extra-terrestrial origin."
Regardless of where the microbes Shkaplerov was referring to came from, this discovery adds credence to a recent study that speculates that the continual rain of dust from outer space could dislodge some of these high-flying germs, and send them on a journey through space where they could potentially be caught up in the atmosphere of another planet, or deposited even closer to home on the ISS. The study, conducted at the University of Edinburgh, also says that the opposite could be true: that microbes from high in the atmosphere of a distant planet could very well be blown across the cosmos, and find their way here to Earth.