Russian scientists on board the International Space Station have reported that sea plankton has been growing on its outside in an "absolutely unique" situation.

"Plankton in these stages of development could be found on the surface of the oceans," said Vladimir Solovyev, head of the Russian ISS orbital mission, as quoted by The Telegraph. "This is not typical for Baikonur [in Kazakhstan]. It means that there are some uplifting air currents which reach the station and settle on its surface."

According to a Russian Itar-Tass news agency report, the life forms were not native to the ISS launch site in Kazakhstan.

NASA scientists have said that sea plankton could potentially have attached itself to the space station from Earth; however, the agency is not officially aware of the find.

"As far as we're concerned, we haven't heard any official reports from our Roscosmos colleagues that they've found sea plankton," NASA spokesman Dan Huot told Space.com.

If the specimens are confirmed to be sea plankton, they may be contaminants that launched into space along with the space module, according to NASA scientist Lynn Rothschild.

Cosmonauts took samples from outside the ISS, but NASA has not confirmed any sea plankton.

"I'm not sure where all the sea-plankton talk is coming from," Huot told Space.com. "The Russians did take samples from one of the windows on the Russian segment, and 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. That's what they were taking samples for."

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