For a number of decades now, astronomers have wondered about water on Mars. Thanks to ESA's Mars Express, much of the speculation has been replaced with facts. Launched on 2 June 2003, Mars Express has changed the way we think of Mars.
Since the Viking missions of the 1970s, planetary scientists have changed their perception of water on Mars several times, passing from the picture of a dry planet to that of a warmer and wetter one. Mars Express's data are now shading a new light on the complex issue of the evolution of water on the Red Planet. "We are re-writing the history of Mars," says Gerhard Neukum, Freie Universitaet Berlin, Germany, and the Principal Investigator on Mars Express's High Resolution Stereo Camera (HRSC). "The big picture of a warm wet Mars is not completely correct. Any warm wet period lasted only a few hundred million years. By four thousand million years ago, it was over," he adds.
Three instruments on Mars Express have been at the centre of this revolution in thought. One is the Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS). Since July 2005, MARSIS has probed beneath the surface of Mars to depths of thousands of metres. This is the first time such investigations have taken place.
"MARSIS has shown that many of the upper layers of Mars contain water ice," says Jeffrey Plaut of the Jet Propulsion Laboratory, Pasadena, who is the co-Principal Investigator on the MARSIS experiment.
The scientists detected abundant water ice in the Martian polar regions and also received a surprise from some of the very first results that MARSIS returned. When the radar passed over the mid northern latitudes of Chryse Planitia, the signals showed a buried impact crater, below the surface. Inside this impact structure was a thick layer of possibly water-ice-rich material. "We are finding reservoirs of ice that have never been seen before," says Plaut, "But we are still puzzling out when and whe
Contact: Agustin Chicarro
European Space Agency