Question

Is there an exoplanet that could have life among all the ones who have been already found?

None of the exoplanets discovered so far appears to be habitable, but there are many uncertainties, about both the properties of the planet and the definition of habitability. The great majority of the planets discovered by radial velocity surveys are giant planets without solid surfaces, and many of these are also in unsuitable orbits, either too close to the star or non-circular. The problem, of course, is a selection effect: radial velocity surveys preferentially detect big planets close to their stars. The most interesting nearby planetary system is called Gliese 581. On April 21, 2009, the planet called Gliese 581e was announced with an approximate mass of 1.9 Earth masses, which is now the smallest known exoplanet around a main sequence star, and hence the most likely to be habitable. Astrobiologists are especially interested in the results that will come from the Kepler mission, which is designed to search for Earth-size planets in the habitable zone of their stars. Successfully launched on March 6, 2009, Kepler is now checked out and is returning excellent data. You can follow the progress of Kepler at (kepler.nasa.gov).

David Morrison
NAI Senior Scientist
June 23, 2009