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http://www.esa.int/esaCP/SEMADOV74TE_Life_0.htmlMars Express and the story of water on MarsEuropean Space Agency16 October 2006For a number of decades now, astronomers have wondered about water onMars. Thanks to ESA's Mars Express, much of the speculation has beenreplaced with facts. Launched on 2 June 2003, Mars Express has changedthe way we think of Mars.Since the Viking missions of the 1970s, planetary scientists havechanged their perception of water on Mars several times, passing fromthe picture of a dry planet to that of a warmer and wetter one. MarsExpress's data are now shading a new light on the complex issue of theevolution of water on the Red Planet."We are re-writing the history of Mars," says Gerhard Neukum, FreieUniversitaet Berlin, Germany, and the Principal Investigator on MarsExpress's High Resolution Stereo Camera (HRSC). "The big picture of awarm wet Mars is not completely correct. Any warm wet period lastedonlya few hundred million years. By four thousand million years ago, it wasover," he adds.Three instruments on Mars Express have been at the centre of thisrevolution in thought. One is the Mars Advanced Radar for SubsurfaceandIonospheric Sounding (MARSIS). Since July 2005, MARSIS has probedbeneath the surface of Mars to depths of thousands of metres. This isthe first time such investigations have taken place."MARSIS has shown that many of the upper layers of Mars contain waterice," says Jeffrey Plaut of the Jet Propulsion Laboratory, Pasadena,whois the co-Principal Investigator on the MARSIS experiment.The scientists detected abundant water ice in the Martian polar regionsand also received a surprise from some of the very first results thatMARSIS returned. When the radar passed over the mid northern latitudesof Chryse Planitia, the signals showed a buried impact crater, belowthesurface. Inside this impact structure was a thick layer of possiblywater-ice-rich material. "We are finding reservoirs of ice that havenever been seen before," says Plaut, "But we are still puzzling outwhenand where the water on Mars was liquid.""The last MARSIS observations have been done on the South Pole," addsGiovanni Picardi, MARSIS Principal Investigator, from the University ofRome "La Sapienza". "The quality of the preliminary results of theadvanced analysis we are still performing are really exciting andpromising, with respect to the main scientific objectives of ourexperiment." The objectives include the detection of subsurface water.The OMEGA Visible and Infrared Mineralogical Mapping Spectrometer hastaken giant steps towards answering that question. OMEGA detectsminerals on the surface of Mars. Three in particular reveal the historyof Martian water. "We have demonstrated that water could have beenstable on Mars's surface but not for very long," says Jean-PierreBibring, Institut d'Astrophysique Spatiale, Orsay, France, and OMEGA'sPrincipal Investigator.OMEGA detected clay-like minerals that form during long-term exposuretowater, but only in the oldest regions of Mars. That suggested waterflowed during the first few hundred million years of the planet'shistory only. When these bodies of water were lost, water thenoccasionally burst from inside the planet but quickly evaporated.During the evaporation they made sulphates, the second mineral thatOMEGA detected. When even this stopped and the remaining water on Marsbecame permanently frozen, then the atmosphere gradually turned thesoilred by creating the third mineral OMEGA detected, ferric oxide.Mars has been like this for thousands of millions of years. "It isremarkable that, for the first time, we have identified where and whenliquid water might have been present on Mars. It is not where onethought of before," says Bibring.The images from the High Resolution Stereo Camera (HRSC) point towardsthe same conclusions. They show the Martian surface in the mostexquisite detail, revealing features just 10 metres across. Theyclearlyshow extremely old Martian regions that have been eroded by flowingwater. The pictures also show a huge valley, Kasei Valles, carved by agigantic Martian glacier that persisted for a thousand million yearsduring the time when the temperature of Mars had dropped too low forliquid water to flow across the surface."We see a clear link between volcanic regions and water flows," saysNeukum. Wherever there has been volcanic activity on Mars, it hasmeltedwater inside Mars and let it flow to the surface. Some of these flowsare recent - geologically speaking. "At the foot of Olympus Mons, HRSCsees evidence for water flows that have happened within the last 30million years," says Neukum.NASA's latest spacecraft, the Mars Reconnaisance Orbiter (MRO), carriesinstruments that lead on from those of Mars Express. Many scientistsfrom the teams at work on MARSIS are now working on the ASI's ShallowRadar (SHARAD) on board MRO. This is tuned to focus on the shallowerlayers of Mars, whereas MARSIS looks deeper. OMEGA's sister instrumenton MRO is the Compact Reconnaissance Imaging Spectrometer for Mars(CRISM). This will look in more detail at minerals on the Martiansurface. However, the instrument only has a small field of view, so itwill need guidance. "They will target primarily the areas that OMEGAhasshown to be interesting," says Bibring."Mars Express has provided unprecedented evidence on the history ofwater on Mars. Now, we look forward to new investigations that willbuild on this legacy," says Augustin Chicarro, Mars Express?s ProjectScientist at ESA.Note to editorsMars Express data is still streaming down from HRSC, MARSIS, Omega butalso the probe's other instruments, PFS, SPICAM, ASPERA, and MaRS. Theyare probing all aspects of the Martian environment - studyingatmospheric gases, searching for eventual biological processes,detecting high altitude clouds and hidden volcanoes and digging intothescavenging effects of the solar wind.For more informationAgustin Chicarro, ESA Mars Express Project ScientistEmail: agustin.chicarro @ esa.intGerhard Neukum, HRSC Principal Investigator, Freie Universitaet Berlin,GermanyEmail: gneukum @ zedat.fu-berlin.deJean-Pierre Bibring, OMEGA Principal Investigator, Institutd?Astrophysique Spatiale - IAS, Orsay, FranceEmail: jean-pierre.bibring @ ias.u-psud.frGiovanni Picardi, MARSIS Principal Investigator Univ. di Roma 'LaSapienza', ItalyEmail: picar @ infocom.uniroma1.itJeffrey Plaut, MARSIS Co-Principal Investigator, NASA/JPL, USAEmail: plaut @ jpl.nasa.gov