LOS ANGELES, Feb. 15 (Xinhuanet) -- The US twin Mars rovers, Spirit and Opportunity, are still working on their extended missions 10 months after their scheduled life-span, the US space agency NASA said Tuesday.

Spirit's miniature thermal emission spectrometer examined this rock, dubbed "Wishstone," and data indicated that the mineralogy of the rocks in this area is different from that of rocks encountered earlier in the plains of Gusev Crater or in the bedrock outcrops examined so far in the "Columbia Hills" inside the crater. (NASA)

    Spirit found a new class of water-affected rock, while its twin, Opportunity finished inspecting its own heat shield and set a new Martian driving record, said NASA's Jet Propulsion Laboratory based in Pasadena, California.

    "This is probably the most interesting and important rock Spirit has examined," said Dr. Steve Squyres, principal investigator for the rovers. The rock, dubbed "Peace," is an exposure of bedrock in the Columbia Hills. The hills are in Gusev Crater, where Spirit landed 13 months ago.

    "This may be what the bones of this mountain are really made of.It gives us even more compelling evidence for water playing a major role for altering the rocks here," Squyres added.

    Observations by Spirit show the rock contains significant amounts of the minerals olivine, pyroxene and magnetite, all of which are common in some types of volcanic rock. The rock's texture appears to be sand-size grains coated with a material loosely binding the rock together. Spirit's rock abrasion tool dug about one centimeter deep in two hours.

    "It looks as if you took volcanic rocks that were ground into little grains, and then formed a layered rock with them cemented together by a substantial quantity of magnesium-sulfate salt," Squyres said in a press briefing.

This image from Opportunity shows a portion of the heat shield that the spacecraft jettisoned shortly before landing. The US twin Mars rovers, Spirit and Opportunity, are still working on their extended missions 10 months after their scheduled life-span, the US space agency NASA said Tuesday. (NASA)

    It could come from liquid water with magnesium sulfate salt dissolved in it, percolating through the rock, then evaporating and leaving the salt behind. Or it could come from weathering by dilute sulfuric acid reacting with magnesium-rich minerals that were already in the rock. Either case involves water, the researchers said.

    Opportunity used its microscopic imager to examine a cross section of the heat shield that protected the spacecraft as it slammed into Mars' atmosphere. This is the first time experts have been able to examine a heat shield after it entered another planet' s atmosphere.

    NASA engineers said they need months to analyze the data, expecting the findings to aid design for future missions.

    Since leaving the heat shield, Opportunity has been traveling south to explore new sites. The rover set a single-day Martian driving record, covering 154.65 meters on Jan. 28. Two days later it broke the record by driving 156.55 meters.

    The first 90 meters of each drive were performed in blind-drive mode, following a route planners created from stereo images from the rover and maps created from orbital imagery. The rest was autonomous driving, with the rover choosing its own route to avoid any hazards it perceived in stereo images taken along the way. Enditem