SEA PLANKTON FOUND ON HULL OF THE INTERNATIONAL SPACE STATION
No one can explain how it got there, as these life forms are not present at the launch point.
The only explanation offered is that perhaps they floated up from the ocean 2oo miles below, something that does not sound very likely. Or, perhaps there was some unknown contamination. Others are willing to believe that primitive life exists outside earth and populates space.
It is a mystery that needs to be researched.