Searching for Water in Exoplanets

Up to now about 50 extraterrestrial planets have been discovered with different optical methods mostly based on the Doppler velocity technique (1, 2). This successful technique allows the detection of giant planets with sufficient mass in order to excite a gravitational wobbling of the central star and it allows the determination of mass, period and distance from the star and eccentricity, but it does not give any chemical information on the atmospheric structure.