As scientists refine their methods, exoplanets are becoming easier and easier to detect. The current count is 163 planets orbiting 97 main-sequence stars, of which only one is even remotely Earth-like. All the others are massive bodies, ranging from “tiny” Uranus-like worlds (at about 15 Earth masses) to super-Jupiters (at thousands of Earth masses). The direct detection of terrestrial planets around stars like our Sun may have to wait until the launch of dedicated satellites such as COROT and Kepler (scheduled for 2006 and 2008, respectively). In the meantime, some researchers have begun to wonder whether these extrasolar gas giants could harbor habitable moons. Our own solar system has four gas giants, and each has been blessed with an abundance of satellites. All these moons are far smaller than the Earth, but six could qualify as planets in their own right if they orbited the Sun: Jupiter's four Galilean satellites Europa, Callisto, Ganymede, and Io; Saturn's Titan; and Neptune's Triton.

Europa is known to have large amounts of water ice, and Titan has a thick atmosphere. If our solar system is not atypical, many of the known exoplanets probably have rich moon systems as well. Caleb Scharf, Columbia University's Director of Astrobiology, has been exploring the conditions necessary for such moons to be habitable. His recent work investigates the conditions necessary for a moon to contain enough water to sustain biological life, at temperatures capable of supporting biological activity.

View: Full Article | Source: Physorg.com