Image: Microscopic view of Humphrey
NASA / JPL / Cornell / USGS
A microscopic image provided by the Spirit rover focuses on the rock known as Humphrey. The yellow and red circles highlight crystal-filled fissures that hint at interaction with water during the rock's formation. The blue and green circles highlight features that were probably created by the rover's scientific tools.
updated 3/5/2004 5:47:40 PM ET 2004-03-05T22:47:40

NASA scientists say their Spirit rover has found more evidence that water once existed on Mars, following close behind the announcement that its twin, Opportunity, sits in a region that was soaked by water in the distant past.

Toiling away in the shadow of its robotic twin, which snagged the Martian water spotlight earlier this week, Spirit made its find by studying Humphrey, a 23-inch-tall (60-centimeter-tall rock at Gusev Crater. The rover found that despite the rock's volcanic beginnings, water apparently seeped through it at one time, allowing minerals to crystallize inside.

"We're not talking about a lot of water here," said Ray Arvidson, deputy principal investigator for the rover mission, during a press briefing Friday at NASA's Jet Propulsion Laboratory in Pasadena, Calif. "But it means Mars is a diverse planet, and that water was there."

Spirit conducted extensive studies of Humphrey with the multiple science tools on its robotic arm. During those studies, which included drilling into Humphrey with the rock abrasion tool then taking images of the area with the microscopic imager, Spirit detected fractures in the rock filled with minerals that were most likely formed in the presence of a tiny amount of water.

The amount of water needed to form the minerals seen in Humphrey is nowhere near that suggested at Meridiani Planum, where Opportunity found signs that the rocks there were once drenched in water. Scientists aren't yet sure whether water existed at Meridiani Planum in the form of a lake, sea or merely groundwater that percolated through rocks on the way to the surface.

"I don't believe it was a groundwater percolation situation here," Arvidson said of Spirit's water evidence.

Most likely, Humphrey's water was mixed with Martian magma, flowing through the rock that later formed as the magma cooled, Arvidson said.

Mars rover scientists said their next step is to look for similar mineral deposits inside future rock targets, and to look even deeper than previous studies once it reaches Bonneville crater, a region that lies at the end of its current drive. Spirit has just left Middle Ground, where Humphrey was located, on an 82-foot (25-meter) drive toward Bonneville.

"When we're up on the rim, we're going to drill deeper and deeper holes into the rock, like 4 millimeters, to get in there and make sure we see the same textures [as at Humphrey]," Arvidson said.

Image: Heatshield
An enlarged portion of a panoramic view taken by the Opportunity rover shows the rover spacecraft's heatshield and a divot that it made when it fell to the surface. The UFO-like heatshield is about a half-mile away from the rover.
Matthew Wallace, mission manager for Opportunity at JPL, said that the terrain around Spirit is gradually becoming more challenging on the approach to Bonneville, largely because it is strewn with rocks. But rover handlers will soon send a new flight software upgrades to both Spirit and Opportunity that should enhance their navigation systems.

"I think we're on track to get it on both vehicles within the next two or three weeks,'" Wallace said.

Meanwhile, the Opportunity rover is expected to make a sweep of the small crater it has spent the last 40 days exploring. The robot was able to photograph a brief eclipse of the sun by the small Martian moon Deimos. They hope to be able to catch a similar eclipse with the larger moon Phobos — which could blot out half the sun or more — in the near future. Those observations, however, lie outside Opportunity's normal operational times.

Mission planners expect Opportunity to leave its crater about the same time Spirit reaches Bonneville in a few weeks.

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