May 26 (UPI) -- Officials with Russia's space agency, Roscosmos, say their scientists have identified plankton and other microorganisms among dust samples collected from the outside of the International Space Station.
"The micrometeorites and comet dust that settle on the ISS surface may contain biogenic substance of extra-terrestrial origin in its natural form," Roscosmos officials said in a news release. "The ISS surface is possibly a unique and easily available collector and keeper of comet substance and, possibly, of biomaterial of extra-terrestrial origin."
NASA officials said they couldn't confirm the story.
"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 in 2014 when reports of plankton on the outside of the ISS surfaced.
Huot said Russian cosmonauts did recently collect dust samples from the outside of their space station module's window.
"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," Huot said. "That's what they were taking samples for. I don't know where all the sea plankton talk is coming from."
Russian officials claim cosmonauts have been collecting dust samples -- 19, so far -- from the outside of the International Space Station since 2010.
Russian scientists believe the ISS spends the majority of its time orbiting through dust left behind by the tails of comets. Scientists have long hypothesized that comets carry the secret ingredients for life and may have delivered the building blocks that sparked life's beginnings on Earth.
Scientists with both NASA and the European Space Agency have proved microorganisms can survive in space. Tardigrades, or water bears, a resilient invertebrate, can withstand a variety of harsh conditions. Researchers have also found microbes in Earth's upper atmosphere.
Despite such discoveries, researchers have yet to announce the discovery of extraterrestrial life.