This week, the Russian space agency stated that several astronauts discovered traces of sea plankton, presumably from Earth, when doing a routine cleaning on the outside of the International Space Station. However, NASA officials remain skeptical of the announcement.

The discovery came during a spacewalk by cosmonauts Olek Artemyev and Alexander Skvortov, who were wiping down windows, also known as illuminators, on the outside of the Russian part of the ISS. After studying the material they used for cleaning with "high precision equipment," they found evidence of plankton and other microorganisms.

"The results of the experiment are absolutely unique," says Vladimir Solvyev, the head of the Russian ISS mission. "We have found traces of sea plankton and microscopic particles on the illuminator surface. This should be studied further."

Although it sounds far-fetched, the plankton may have hitched a ride from Earth to space in 1998 when the ISS originally launched. However, plankton isn't usually found in the area where the station launched from. But this is still the most likely explanation, according to most scientists.

According to Solovyev, however, the plankton, which are often found on the surface of Earth's oceans, came from those oceans on an air current and "uplifted" 260 miles to the station.

The only problem with this discovery is that NASA wasn't aware of it until it started making headlines. No official reports about the plankton have reached NASA from the Russian space agency.

"What they're actually looking for is residues that can build up on the visually sensitive elements, like windows, as well as just the hull of the ship itself that will build up whenever they do thruster firings for things like re-boosts," says Dan Huot, a NASA spokesperson. "That's what they were taking samples for. I don't know where all the sea plankton talk is coming from."

NASA scientists, though, believe if the plankton is actually on the ISS, it probably came from Earth on one of the space station's modules. The agency hasn't commented on the Russian theory about rising air currents, but it seems they're not buying it.

Plankton, and other microbes, can survive in the harsh conditions of space, so the plankton living on the ISS isn't a huge surprise. Scientists have also even found microbes and bacterial life in Earth's upper atmosphere.

These hearty microbes are a concern for upcoming space exploration missions, particularly those to other planets, when we don't want Earth microbes contaminating any equipment and confusing the search for alien microbes.