Traces of plankton and other microorganisms have been found living on the exterior of the International Space Station (ISS), according to Russian space officials.
They claim the plankton were not carried there at launch – but are thought to have been blown there by air currents on Earth.
Incredibly, the tiny organisms were found to be able to survive in the vacuum of space despite the freezing temperatures, lack of oxygen and cosmic radiation.
The discovery was made during a routine spacewalk by Russian cosmonauts Olek Artemyev and Alexander Skvortsov, who were launching nanosatellites into space.
They used wipes to polish the surface of windows - also known as illuminators - on the Russian segment of the ISS and later found the presence of plankton and other microorganisms using ‘high-precision equipment’.
‘The results of the experiment are absolutely unique,’ said the head of the Russian ISS orbital mission Vladimir Solovyev.
‘We have found traces of sea plankton and microscopic particles on the illuminator surface. This should be studied further.’
The plankton are not known to be indigenous to Baikonur, Kazakhstan, where the Russian modules of the station blasted off from.
Mr Solovyev is not absolutely sure ‘how these microscopic particles could have appeared on the surface of the space station,’ according to Russian news agency Itar-Tass.
But he thinks they they may have been 'uplifted' to the station at an altitude of 260 miles (420km).
‘Plankton in these stages of development could be found on the surface of the oceans,' he said ( via dailymail.co.uk ).
‘This is not typical for Baikonur. It means that there are some uplifting air currents which reach the station and settle on its surface.’
Nasa is yet to comment on what this might mean for the American segment of the ISS, and whether similar findings have been made in the past.