Tardigrades Survived 10 Days of Open Space

In September 2007, the European Space Agency strapped two species of tardigrade to the outside of the Foton-M3 satellite and pointed them at the sun for ten days. Most lived.

These eight-legged invertebrates, rarely larger than a poppy seed, can enter a desiccated state in which water content drops below 3% and metabolism essentially stops. Ingemar Jönsson, a zoologist at Kristianstad University in Sweden, sent dehydrated Richtersius coronifer and Milnesium tardigradum into low Earth orbit aboard the BIOPAN-6 platform.

Vacuum alone was survivable. Combined with full-spectrum UV-A and UV-B, the survival rate dropped sharply, but a few M. tardigradum still rehydrated and laid viable eggs back on Earth. They became the first animals known to survive direct exposure to space.

Why it matters is not that tardigrades came from space — that hypothesis is unsupported. It is that the dormant state, called a tun, is more robust than biologists had assumed. The conditions previously considered sterilizing turn out not to be, which has implications for planetary protection rules and the search for life on Mars.

The result re-raised an older question: what is the actual ceiling? A 2017 paper by David Sloan, Rafael Alves Batista, and Avi Loeb at Oxford modelled tardigrade survival against asteroid impacts, gamma-ray bursts, and a nearby supernova. Their conclusion was that no plausible astrophysical event short of the Sun itself going supernova would wipe the lineage out.

If life on Earth ends, in other words, it probably will not be tardigrades that go first.