Havens, Hells, and H2O
Several hundred meters above the ocean floor, something like a flying saucer wheels across the underwater landscape. Carried within the giant swirling vortex are chemicals, warmth, and the larval forms of living creatures, bound on an uncertain journey that began above a volcanic vent and may end with the colonization of a new vent hundreds of kilometers away. Deep below the ocean floor, microbial moles bore through solid rock, assimilating chemical energy as they dissolve their way along. And on the floor itself, 700 meters down, strange worms dwell contentedly in explosive methane ice, tending kitchen gardens of bacteria.
A vision of alien life? Absolutely. But these particular aliens happen to live here on Earth. They're among the mind-boggling discoveries of the past few years, encouraging the view that life may be able to adapt to all sorts of bizarre extraterrestrial regimes, perhaps including some that are on neighboring worlds in the solar system.
The notion of life as a delicate flower that needs careful nurturing under mild conditions has faded into the past—and with it the belief that life might be rare. Today, many astrobiologists have a growing sense that life is uncannily good at exploiting whatever niches the universe tosses its way. It seems almost to relish the challenge, popping up in the most outrageous places, dining happily on toxic waste. Wherever a supply of organics, liquid water, and energy exist together, scientists now suspect living things may not be far away. The question then becomes, in what sort of places do these essentials coincide. Where are the havens for life in space?
Suitable energy sources seem less of a problem than before, now that thermal energy welling up from inside a world can be added to the repertoire