Tardigrade

In September 2007 dried-out tardigrades (water bears) rode on the European Space Agency's FOTON-M3 mission and spent 10 days exposed to the vacuum and radiation of space. Many survived, some even endured strong solar ultraviolet light, and survivors went on to reproduce.

They survived in a dried, dormant state. That does not make them indestructible in every setting.

Context

Tardigrades are microscopic animals, usually well under a millimetre long, found in moss, soil and water worldwide. When their surroundings dry out they can enter a state called cryptobiosis, shrinking into a dried form often called a tun and slowing their metabolism to a very low level. Revived with water, they can move and feed again.

The 2007 experiment, known as TARDIS, flew on a capsule launched by Russia for the European Space Agency. Groups of dried animals were exposed to vacuum alone, to vacuum plus different parts of the solar ultraviolet spectrum, and to cosmic radiation. Exposure to vacuum and cosmic radiation alone caused little harm to many animals, but full solar ultraviolet radiation killed most of them, with only a small number surviving.

These results show a remarkable tolerance, not invincibility. Active, hydrated tardigrades are far more vulnerable, and the tests covered a particular set of conditions for 10 days. Later laboratory work has explored how special proteins and repair systems may protect their cells, which interests researchers studying radiation damage and dry preservation of biological material.