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SCIENCE. Cont'd.

Photo: Flyover from the submerged northeast Hellas Planitia to the Hesperia Planum.

Squyres, a Cornell University scientist and principal investigator for the science instruments on Opportunity, said the rover's study of formations near its landing site show that liquid water once flowed there, changing the chemistry and composition of the rocks. Asked how long ago water might have existed on Mars, Squyres said, "It's very, very difficult to infer age simply by looking at pictures, by measuring this kind of composition. What you really need is samples brought back." He did say that whatever process in the past produced the water, "There's nothing like this going on on Mars today." The twin rovers now on Mars will not return to Earth, but will remain on the red planet after they stop functioning. U.S. President George W. Bush has proposed sending manned flights to the moon and Mars. Opportunity landed five weeks ago near an exposed bedrock embedded in the wall of a small crater. The rover conducted a chemical analysis of the outcrop, including a rock named El Capitan by scientists, and found a concentration of sulphur rich in magnesium, iron and other sulfate salts. Opportunity's instrument also detected jarosite, an iron sulfate mineral. On Earth, such minerals would have formed in water and the presence of jarosite suggests an acid-rich lake or hot springs environment, scientists said. John Grotzinger, a geologist from the Massachusetts Institute of Technology in Cambridge, said the evidence of water also includes three direct visual observations: the presence in El Capitan of small voids, called vugs; the presence of spherules, and the layering of the rock. Images shows that El Capitan is pocked with one-centimetre-long indentations or voids that may have once contained salt minerals. Such voids, or vugs, form when crystals of salt minerals aggregate within a rock sitting in salty water. Later processes cause the crystals to disappear, leaving behind the voids within the rock.

Photo: Flyover from the submerged Isidis Planitia to the Hesperia Planum. The Du Martheray crater is in front.

BB-sized particles, called spherules, also formed in the rock. These can be formed from molten droplets originating from meteor impacts or from volcanic action, or they can precipitate from solution inside of porous rock. NASA scientists said that since the spherules are randomly distributed they probably formed in water. If they were of volcanic or impact origin, the spherules would probably concentrate in rock layers that were exposed at the time of those events, the researchers said in a statement. The rock also has layers in a pattern called crossbedding that can be formed by water or wind action, the statement said. More study of the target rocks is planned. Officials said they will manoeuvre the six-wheeled rover closer to the outcrop to get closer, more detailed views.

Note: Gallery of amazing photos on the following pages.