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The curious case of space plankton

It’s increasingly becoming clear that space is a more hospitable environment than was assumed.

The Sun, seen from the International Space Station. Photo: STS-129/Nasa
The Sun, seen from the International Space Station. Photo: STS-129/Nasa

While on earth it may be a difficult time for US-Russia relations, above us the International Space Station (ISS) remains an outpost of collaboration between the two countries. At least, that’s the idea. In practice, communication may be breaking down between the astronauts on board humanity’s most expensive scientific experiment.

Russia’s Itar-Tass news agency reported on 19 August that Roscosmos, the Russian space agency, had found sea plankton living on the outside of the ISS. It quoted the ISS mission chief for Roscomos, Vladimir Solovyov, who said they were found outside the Russian section of the ISS. This is surprising, as none of the astronauts or agencies involved put them there. Indeed, Nasa doesn’t quite believe it. Its spokesperson said that Nasa hadn’t heard any official reports from its Russian colleagues.

Plankton (from the Greek for “drifter”) are micro-organisms such as bacteria and algae that float around in water and are unable to swim against the current. We don’t know yet what kind of plankton Roscosmos claims to have found. Yet the assertion is plausible – if unlikely.

It’s increasingly becoming clear that space is a more hospitable environment than was assumed. It’s a mistake we can be forgiven for making – after all, for human-sized animals, space is a terrible place. Yet, for some organisms, it is no more challenging than some of earth’s more intimidating ecological niches, such as volcanic vents at the bottom of the oceans or Antarctica. The high radiation, lack of pressure and extremes of heat and cold in space are tough but not deadly to creatures that exist on the scale of fractions of a millimetre or less.

We know this because for years the ISS has been running experiments to test micro-organism hardiness. In 2008, bacteria living in rocks found in Devon were put outside the ISS and left there for 533 days. When the rocks were brought back to earth, the bacteria happily began multiplying again. These were ordinary Gloeocapsa cyanobacteria, of a kind found all over the world. Several other experiments – with lichen and with the particularly hard-to-kill tardigrades (eight-legged creatures known as “water bears”) – have also shown how some life forms can hibernate until conditions improve. This is why the panspermia hypothesis – that earth life originally came on an asteroid or comet – has been gaining traction in recent years.

If there are plankton living on the outside of the ISS, they could have come from a contaminated component, or been blasted on to the station by thrusters from a supply ship. Cleaning spacecraft is exceedingly difficult – Nasa is reasonably certain that its landers, including Viking and Curiosity, were probably not completely sterile when they were launched. Perhaps when human beings finally travel to Mars, we won’t be the first earthlings there. Some of our microscopic relatives could be waiting for us. 

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