NASA

There are a lot of things in space, but terrestrial sea plankton was not one of them --at least, so we thought. Yet traces of the microorganisms were found on the windows of the International Space Station, as reported by Russia's Itar-Tass news agency.

Experiments had previously shown that microorganisms such as bacteria are capable of surviving in space, and, further, propagating endospores -- but sea plankton is certainly a new discovery, Vladimir Solovyev, chief of the Russian ISS orbital mission, told the news agency.

"The results of this experiment are absolutely unique," he said. "We have found traces of sea plankton and microscopic particles on the illuminator [window] surface. This should be studied further."

As for how the plankton got there in the first place, researchers are yet unclear, although they do have some theories.

"[Plankton in] such phases of development is found on the surface of the ocean. It isn't characteristic to Baikonur [Cosmodrome, from where supplies are launched to the space station]," Solovyev said. "It turns out that there are some rising air currents, which settle on the surface of the station."

The first parts of the ISS were launched in 1998, which also means it's not impossible that the plankton has been living up there for quite some time.

Solovyev also noted that the surface of the space station is quite heavily polluted from various activities that occur on and around it, such as the arrival and departure of supply craft. "We are conducting special works to polish somehow and put the illuminators in order. This is particularly needed during long space flights," he said.