NASA says rover Opportunity still stuck in Mars sand
LOS ANGELES, May 24 (Xinhua)-- The Mars rover Opportunity is trying to escape from a sand trap after being stuck for three weeks, the US National Aeronautics and Space Administration (NASA) said on Tuesday.

The rover has been hindered by soft sand, but traction is difficult in the ripple-shaped dune of windblown dust and sand that Opportunity drove into on April 26, NASA's Jet Propulsion Laboratory (JPL) said in a statement.

Since it began trying to get out on May 10, the rover has advanced only 26 centimeters in 11 days. Without the slippage caused by the rover's wheels spinning in the sand, Opportunity could have driven 46 meters in eight drives.

"If Opportunity gets free, its next task will be examining the site to give the rover team a better understanding of how this ripple differs from dozens Opportunity easily crossed," said Jim Erickson, manager for the Mars Exploration Rover project at JPL in Pasadena.

However, Opportunity's twin, Spirit, has been busy finding new clues inside Mars' Gusev Crater to a wet and violent early Martian history.

"Spirit has finally found the kind of geology you can really sink your teeth into," said Steve Squyres, principal investigator for the Mars rovers' science instruments.

According to Squyres, multiple layers of rock in the "Columbia Hills" Spirit is exploring suggest successive deposits of water- altered explosive debris.

"In the last few weeks, we have gone from a state of confusion about the geology of the 'Columbia Hills' to having real stratigraphic sequence and a powerful working hypothesis for the history of these layers," said Squyres.

For several months, Spirit climbed a flank of "Husband Hill," the tallest in the range. The slope closely matched the angle of underlying rock layers, which made the layering difficult to detect.

Spirit reached an intermediate destination then continued uphill and looked back to see the layering. That was the critical moment when it all began falling into place.

It has been examining rocks in a series of outcrops. Some of the rocks contain the mineral ilmenite, not found previously by Spirit.

According to team scientists, ilmenite is a titanium-iron oxide formed during crystallization of magma. Its occurrence is evidence for diversity in the volcanic rocks in the Gusev region.

Rocks from different layers share compositional traits, high in titanium and low in chromium, which suggests a shared origin. However, the degree to which minerals in rocks have been chemically altered by exposure to water or other processes varies greatly. The textures also vary.

"Our best hypothesis is we're looking at a stack of ash or debris that was explosively erupted from volcanoes and settled down in different ways," Squyres said.

"We can't fully rule out the possibility the debris was generated in impact explosions instead of volcanic ones. But we can say, once upon a time, Gusev was a pretty violent place. Big, explosive events were happening, and there was a lot of water around."

The rovers have worked under harsh Martian conditions much longer than expected. They have been studying geology on opposite sides of Mars for more than a year since successfully completing their three- month primary missions.


Publication date: 2005-05-25