There are plenty of places you'd expect to find plankton -- lakes, oceans, reruns of SpongeBob Squarepants -- but the external hull of the International Space Station probably wouldn't make your list. And yet, that's exactly where Russian cosmonauts claim to have found some, according to Russian news agency ITAR-TASS. As it happens, you may want to take that report with a grain of salt: We reached out to NASA for comment and spokesperson Dan Huot said the organization has received "zero official data" from Russia's Roscosmos space agency to corroborate these claims. Looks like it'll be a while before we actually get to the bottom of this.Let's say for the sake of argument, though, that cosmonauts collecting residue samples from the space station's windows (sorry, illuminators) really did find tiny sea organisms clinging to them. How on earth did they get there? A few theories are floating around right now: Russian ISS mission chief Vladimir Solovyev wondered if air currents lifting plankton up through the atmosphere were to blame, while NASA scientist Lynn Rothschild told Space.com that the tiny organisms could've hitched a ride on a space station module as it blasted into orbit. If this all pans out, it may just mean that those little water-dwellers -- like bacteria and tardigrades -- are hardier than we gave them credit for.