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By Barrie Jones

Astrobiology (also called exobiology) comprises the search for life beyond the Earth and the study of any such life that might be found. The search extends throughout the Solar System, particularly the planet Mars, which could well have developed life in its warmer and wetter early history, and Europa - one of the large satellites of Jupiter, which probably has an ocean under its icy carapace maintained by tidal heating from Jupiter. Saturn's large satellite Titan has a thick atmosphere that might resemble that of the Earth at about the time life was emerging here.

The search also extends beyond the Solar System. We have already discovered giant planets around over 100 stars, and as soon as planets of about the mass of the Earth are found in the habitable zones of their stars they will be investigated to see if they are potential or actual habitats. Space telescopes proposed for launch around 2015 would make such investigations, in particular the European Space Agency's Darwin and NASA's Terrestrial Planet Finder.

It is believed that the most likely form of extraterrestrial life will have the same broad basis as life on Earth - complex carbon compounds and liquid water. Consequently astrobiology includes the study of life on Earth, particularly its origin and the wide range of habitats that it occupies, including 'extremophiles' that can live at temperatures over 100C and in other extreme conditions. This ensures that we are not overly narrow in our search for life elsewhere.

Astrobiology is a rapidly growing, interdisciplinary area that is already one of the most exciting areas in science, and promises to remain so throughout this century.

Exo fig Exo fig
A possible configuration of the Darwin infrared telescope. Each aperture is a few metres across and they are spaced by a few tens of metres (courtesy Alcatel) A notional hydrobot, searching a Europan ocean for an acquatic biosphere (courtesy JPL/Caltech/NASA)


Frequently asked questions:
  • What are the chances of finding extraterrestrial life?
    Most scientists regard it as beyond reasonable doubt that there is life elsewhere in our Galaxy of about 200,000 million stars, and in the billions of galaxies beyond our own. It is also conceivable that there was once life on Mars and might still be beneath its surface. Europa could still have an acquatic biosphere. Quite how far any such life has advanced is a more tricky question. Life on Earth started as single cells, such as bacteria, and for most of Earth history remained single-celled. It is possible that evolution to plants and animals is rare, leaving the Earth alone in the galaxy as an abode of complex creatures, including intelligent creatures.
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