Lichens are strange organisms, a partnership between a fungus that offers shelter, water and minerals, and an alga or cyanobacterium that supplies food from their photosynthesis. And even though lichens tend to be modest to look at, they are so incredibly tough that some can even survive the harsh environment of space.
When lichens were attached to the outside of the International Space Station for 18 months they survived the vacuum of space, no water, extreme temperatures and the full onslaught of radiation and ultraviolet rays from the sun, and carried on photosynthesising.
Lichens that were kept in a simulated Martian environment on Earth survived and were active, raising the prospect that life could exist on Mars, where the environment is intensely dry and cold, with low atmospheric pressure and radiation bombardment. In fact, lichens can cope with radiation 12,000 times the lethal dose for humans and still carry on photosynthesising, although their reproduction can be harmed. However, bacteria given the same treatment died. There is even a thought that life on Earth, or any other planet, could conceivably have been spread through space by lichens hitching a ride on meteorites, comets or asteroids.
