What’s crusty, grows on bare rock and appears barely alive? Lichens. Many also grow on trees, but you’d be hard pressed in northern Minnesota to find a rock face not spattered with pale green, yellow and orange lichens.
These amazing creatures are a happy marriage or symbiosis of fungi and algae. The fungus provides a home for the algae; the algae provide food for the fungus via photosynthesis.
In 2008 scientists with the European Space Agency (ESA) sent the suitcase-sized Expose-E to the space station filled with 664 organic compounds and a variety of living organisms to see how they’d survive exposed to the vacuum and radiation-filled environment of space. Here on Earth the atmosphere not only provides essential air for respiration but serves to shield living things from dangerous cosmic rays and the full brunt of UV or ultraviolet radiation from the sun.
The samples were exposed to open space for 18 months. While insulated to a degree by the space station, the assortment experienced airlessness, “hard” ultraviolet radiation, cosmic rays and temperatures constantly rising and falling between 10 and 104 degrees F.
So who came out on top? The lichens of course! Xanthoria elegans, an attractive orange lichen gathered from the mountains of Spain, “were the best survivors we know”, said René Demets, a biologist working in ESA. They put themselves into “off mode” while waiting for better days to return. Once returned to Earth, the symbionts roared back to life after a good soak in the water. Think of the healing power of a hot shower after a physically demanding day.
Water vaporizes almost immediately from living things exposed to the vacuum of space. Only animals and plants capable of carrying on in extremely dry conditions can tough it out. Besides lichens and some dried plant seeds, tardigrades (also called water-bears), brine shrimp and larvae of an African midge are the only animals known to survive the means streets of outer space.
All this talk of living things surviving outside the planet’s protection may have you wondering if life might not have come from elsewhere. Maybe as bacteria tucked under the stony skin of a meteorite. It certainly seems possible.
Of course there are two ways to tango. Life on Earth could have been launched by asteroid impact into outer space to potentially seed other planets. Seeing how common invasive species are – everything was once an invasive species, right? – I wouldn’t be surprised at all if life hitched a ride to parts unknown by the most unlikely paths.
I’ll often see lichens on my walks and wonder if they’re dead or alive, especially after a long dry spell. Some of them crumble away at the touch. Next time I’ll have more faith.
To read the complete set of articles on the Expose-E mission, click HERE for the May 2012 issue of Astrobiology Magazine.