As the long quest for alien life goes on and with the discovery of earth-like planets outside the solar system in distant galaxies, here is a surprising find in our own neighbourhood. NASA's Cassini spacecraft has discovered evidence that points to the existence of an underground ocean of water and ammonia on Saturn's moon Titan. The findings made using radar measurements of Titan's rotation appear in the March 21 issue of the journal Science. With its organic dunes, lakes, channels and mountains, Titan has one of the most varied, active and Earth-like surfaces in the solar system. Nineteen passes Members of the Cassini mission's science team used Cassini's radar to collect imaging data during 19 separate passes over Titan between October 2005 and May 2007. The radar can see through Titan's dense, methane-rich atmospheric haze, detailing never-before-seen surface features and establishing their locations on the moon's surface. Using data from the radar's early observations, the scientists and radar engineers established the locations of 50 unique landmarks on Titan's surface. They then searched for these same lakes, canyons and mountains in the reams of data returned by Cassini in its later flybys of Titan. They found prominent surface features had shifted from their expected positions by up to 19 miles. Crust movement A systematic displacement of surface features would be difficult to explain unless the moon's icy crust was decoupled from its core by an internal ocean, making it easier for the crust to move. The team members believe that about 62 miles beneath the ice and organic-rich surface is an internal ocean of liquid water mixed with ammonia. The study of Titan is a major goal of the Cassini-Huygens mission because Titan may preserve, in deep-freeze, many of the chemical compounds that preceded life on Earth. The moon's atmosphere is 1.5 times denser than Earth's. The combination of an organic-rich environment and liquid water is very appealing to astrobiologists. Further study of Titan's rotation will enable understanding of the watery interior better, and because the spin of the crust and the winds in the atmosphere are linked, seasonal variation in the spin in the next few years may be seen. The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The mission is managed by the Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena. The Cassini orbiter also was designed, developed and assembled at JPL. The Cassini radar will be used to investigate the surface of Saturn's moon Titan by taking four types of observations: imaging, altimetry, backscatter, and radiometry. In the imaging mode of operation, the radar instrument will bounce pulses of microwave energy off the surface of Titan from different incidence angles and record the time it takes the pulses to return to the spacecraft. These measurements, when converted to distances (by multiplying by the speed of light), will allow the construction of visual images of the target surface. Radar will be used to image Titan because the moon's surface is hidden from optical view by a thick, cloud-infested atmosphere: radar can