Astronomy

A patch of Martian soil analyzed by NASA’s rover Spirit is so rich in silica that it may provide some of the strongest evidence yet that ancient Mars was much wetter than it is now. The processes that could have produced such a concentrated deposit of silica require the presence of water.

The alpha particle X-ray spectrometer, a chemical analyzer at the end of Spirit’s arm, had measured a composition of about 90 percent pure silica for this soil. Exploring a low range of hills inside a Connecticut-sized basin named Gusev Crater, Spirit had previously found other indicators of long-ago water at the site, such as patches of water-bearing, sulfur-rich soil; alteration of minerals; and evidence of explosive volcanism.

One possible origin for the silica could have been interaction of soil with acid vapors produced by volcanic activity in the presence of water. Another could have been from water in a hot spring environment. The latest discovery adds compelling new evidence for ancient conditions that might have been favorable for life, according to members of the rover science team.

Spirit and its twin rover Opportunity completed their original three-month prime missions in April 2004. Both are still operating, though showing signs of age. One of Spirit’s six wheels no longer rotates, so it leaves a deep track as it drags through soil. That churning has exposed several patches of bright soil, leading to some of Spirit’s biggest discoveries at Gusev, including this recent discovery. The newly discovered patch of soil has been given the informal name “Gertrude Weise,” after a player in the All-American Girls Professional Baseball League.

The Spirit’s miniature thermal emission spectrometer provides mineral composition information about targets viewed from a distance. The indications it found for silica in the overturned soil prompted a decision this month to drive Spirit close enough to touch the soil with the alpha particle X-ray spectrometer. Silica commonly occurs on Earth as the crystalline mineral quartz and is the main ingredient in window glass. The Martian silica at the Gertrude Weise patch is non-crystalline, with no detectable quartz.

Spirit worked within about 50 yards of the Gertrude Weise area for more than 18 months before the discovery was made. Meanwhile, on the other side of the planet, Opportunity has been exploring Victoria Crater for about eight months. Opportunity had completed the initial survey of the crater’s rim and is now headed back to the area called Duck Bay, which may provide a safe path down into the crater.

Source: marsrovers.jpl.nasa.gov

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