Meridiani Planum: "Drenched"
Long ago, parts of Mars were soaked in liquid water, say scientists analyzing data from NASA's Mars rover Opportunity.
March 2, 2004: Some rocks at Opportunity's landing site in Meridiani Planum on Mars were once soaked in liquid water. Members of the Mars Exploration Rovers' international science team presented the evidence today to news reporters at NASA Headquarters in Washington, DC.
Here are some of the clues that water formerly pervaded an outcropping of rocks where Opportunity has been working:
(1) The rover's alpha particle X-ray spectrometer found lots of sulfur in the outcrop. Related clues from that instrument and the miniature thermal emission spectrometer suggest the sulfur is in the form of sulfate salts (similar to Epsom salts). On Earth, rocks containing so much salt either formed in water or, after formation, were soaked in water a long time.
Above: These spectra show that a rock dubbed "McKittrick" near the Mars Exploration Rover Opportunity's landing site at Meridiani Planum, Mars, possesses the highest concentration of sulfur yet observed on Mars. [More]
(2) The rover's Moessbauer spectrometer detected jarosite, a hydrated iron sulfate mineral that could result from the target rock spending time in an acidic lake or acidic hot springs environment.
(3) Pictures from Opportunity's panoramic camera and microscopic imager show many--"about the size of pennies," says Squyres--in an outcrop rock selected for close-up examination. These holes, or "vugs," match the distinctive appearance of Earth-rock vugs that form where crystals of salt minerals grow inside rocks that sit in briny water then disappear by eroding or dissolving.
Right: A spherule in a region of the rock outcrop dubbed "El Capitan." The area in this image, taken on Sol 28 of the Opportunity mission, is 1.3 centimeters (half an inch) across. 
(5) Some of the spherules in pictures from the microscope appear to have stripes that correspond to layering of the matrix rock around them. This would be consistent with the interpretation that the spherules are concretions that formed inside a wet rock.
There is still much to learn: When was the area wet? And how long did the wet conditions last? How was the water collected--e.g., in a salty lake or sea? How deep was the water? Scientists and engineers plan to keep Opportunity busy in the days ahead looking for more clues that might answer some of these questions.
Visit http://marsrovers.jpl.nasa.gov for the latest information about Spirit and Opportunity.