Spirit, Opportunity Rovers Completed Original Missions In 2004

A patch of Martian soil analyzed by NASA's rover Spirit is so rich in silica 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 rover science team heard from a colleague during a recent teleconference that 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, according to the agency.

"You could hear people gasp in astonishment," said Steve Squyres of Cornell University in Ithaca, NY and principal investigator for the Mars rovers' science instruments. "This is a remarkable discovery. And the fact that we found something this new and different after nearly 1,200 days on Mars makes it even more remarkable. It makes you wonder what else is still out there."

Spirit's miniature thermal emission spectrometer observed the patch of soil, and Steve Ruff of Arizona State University, Tempe, noticed its spectrum showed high silica content. The team has already laid out plans for further study of the soil patch and surrounding deposits.

A thermal emission spectrometer (TES) is both an instrument and a technique. It measures the thermal infrared energy (heat) emitted from a planet and is capable of producing two-dimensional images of Mars' surface, according to Arizona State University.

While exploring a low range of hills inside a basin named Gusev Crater, the rover found other evidence of water, such as patches of water-bearing, sulfur-rich soil; alteration of minerals; and evidence of an explosive volcano.

"This is some of the best evidence Spirit has found for water at Gusev," said Albert Yen, a geochemist at NASA's Jet Propulsion Laboratory, Pasadena, CA.

Some possible explanations for the silica could have been interaction of soil with acid vapors produced by volcanic activity in the presence of water or perhaps water in a hot spring environment. This latest discovery adds compelling new evidence that conditions, at some point in the planet's history, might have been able to sustain life.

"What's so exciting is that this could tell us about environments that have similarities to places on Earth that are clement for organisms," said David Des Marais, an astrobiologist at NASA's Ames Research Center, Moffett Field, CA.

Spirit and its twin rover, Opportunity, actually completed their original three-month missions in April 2004. But, they are still operating, although their age is starting to show. One of Spirit's six wheels no longer rotates, so it leaves a deep rut as it drags through the soil.

However, age does have its benefits: those ruts are what exposed several patches of bright soil, leading to some of Spirit's biggest discoveries at Gusev, including this one.

"This unexpected new discovery is a reminder that Spirit and Opportunity are still doing cutting-edge exploration more than three years into their extended missions. It also reinforces the fact that significant amounts of water were present in Mars' past, which continues to spur the hope that we can show that Mars was once habitable and possibly supported life," said Doug McCuistion, director of NASA's Mars Exploration Program.

The newly discovered patch of soil has been dubbed "Gertrude Weise," after a player in the All-American Girls Professional Baseball League, according to Ray Arvidson of Washington University in St. Louis, deputy principal investigator for the rovers.

"We've looked at dozens of disturbed soil targets in the rover tracks, and this is the first one that shows a high silica signature," said Ruff, who last month proposed using Spirit's miniature thermal emission spectrometer to observe this soil.

The TES provides mineral composition information from a distance. The discovered silica prompted a decision this month to drive Spirit close enough to touch the soil with the alpha particle X-ray spectrometer (APXS).

The APXS determines the elemental chemistry of rocks and soils using alpha particles and X-rays, according to NASA. 

Silica commonly occurs here 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, and has no detectable quartz.

"This discovery has driven home to me the value of in-depth, careful exploration," Squyres said. "This is a target-rich environment, and it is a good thing we didn't go hurrying through it."

Meanwhile, on the other side of the planet, Opportunity has been exploring the Victoria Crater for about eight months.

"Opportunity has 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," said John Callas, project manager for the rovers at JPL, a division of the California Institute of Technology, Pasadena, which manages the Mars Exploration Rover project for NASA.

FMI: www.nasa.gov/rovers, http://tes.asu.edu/