Chloride Deposits Found On Mars

NASA's Mars Odyssey spacecraft has detected fields of chloride deposits, an elusive mineral formation associated with water evaporation, on the red planet. A team of researchers led by Mikki M. Osterloo at the University of Hawaii, Manoa, report that the spacecraft's thermal emission imaging spectrometer spotted over 200 patches of the chloride deposits (shown in blue) on Mars's southern highlands, where the planet's most ancient rocks lie (Science 2008, 319, 1651). They confirmed their results with the help of data from NASA's Mars Global Surveyor and Mars Reconnaissance Orbiter spacecraft. The authors show that the fractured, polygonal shapes of the deposits indicate they were dissolved in standing or subsurface water, which eventually evaporated, leaving the minerals. A thinner, less well-developed morphology would be expected if the chloride had been spewed from volcanoes-another possible scenario. The authors believe the deposits formed between 3.5 billion and 3.9 billion years ago, when Mars may have been warmer and wetter. The deposits are "evidence of the presence of extensive reservoirs of surface and/or subsurface groundwater in the planet's early history," the authors write.