Extremophiles are organisms that live in environments generally considered too extreme to be hospitable to most other organisms. This can include extremes of temperature, pressure and acidity. In fact, some extremophiles thrive in exotic environments and cannot survive in more temperate settings. Microbal life Carleton College: Who are the extremophiles?

Extremophiles are of significant interest to the field of astrobiology, which is concerned with the search for extraterrestrial life. Because extremophiles can survive in severe conditions, many of which are replicated on other worlds or in outer space, it is believed that extremophile bacteria might be found in the soil of Mars, on other planets or on asteroids.NASA: Ask an astrobiologist A September, 2008 study published in Current Biology stated that the nearly microscopic animal known as a 'water bear' was able to survive in space for 10 days.New Scientist Space: 'Water bears' are first animal to survive space... (September 8, 2008)