Mars rover strikes 'pot of gold' with most bizarre rock yet seen

This close-up image, taken by the Mars rover Spirit, highlights the nodular nuggets that cover the rock dubbed "Pot of Gold." These enigmatic features appear to stand on the ends of stalk-like projections. NASA/JPL/Cornell

By David Brand

PASADENA, Calif. -- As the rover Spirit celebrates its first six months on Mars at the end of this week (it bounced down Jan. 3), the vehicle has made a remarkable discovery of a type of rock formation never seen before, with a bizarre shape and chemistry that might hold yet more clues to the previous existence of water on the planet.

At a press briefing at the Jet Propulsion Laboratory (JPL) here June 25, Cornell astronomer Steven Squyres, the leader of the Mars rover mission's scientific program, declared, "This is a remarkably strange-looking rock, and I will be very honest with you in saying we have not got this figured out yet."

The softball-size rock was found by Spirit in the lower reaches of the Columbia Hills, where the rover arrived after a 2.5-kilometer trek across the plains from its landing site in the Gusev Crater. "We completed this very long trek across the plains hoping we would find something different, and we have. We may have a water story here," said Squyres, who is professor of astronomy at Cornell.

Dubbed "Pot of Gold," the rock has been analyzed by the rover's spectrometers and has been found to contain hematite, a mineral often formed in the presence of water.

Squyres

A panoramic camera image shows a rock with thin planar features, but the microscopic images show something "dramatically different," said Squyres: tiny stalks with irregularly shaped nuggets on their tips, which he characterized as looking like "jellybeans on the end of toothpicks." He added, "I don't know how these things formed, and they are driving me nuts, to be perfectly honest."

Spirit will spend some time performing chemical tests on Pot of Gold. Hematite forms in a number of different ways, Squyres explained, many of them involving water, "but the key is, you can tell the difference between a watery origin for hematite and a non-watery origin if you can measure other stuff that goes along with it -- if you can figure out what other minerals are present."

Hematite already has been discovered by Spirit's twin rover, Opportunity, on the opposite side of Mars, when it examined rocks in its landing site, dubbed "Eagle Crater." Hematite identified from orbit was NASA's key reason for choosing Opportunity's landing site.

Opportunity now is slowly inching its way down the slopes of another crater, dubbed "Endurance." Squyres noted at the press briefing that the rover has driven far enough into the stadium-size crater to put it within reach of three layers of rock beneath a sulfate-rich layer. The rover's instruments have analyzed the layers as containing sulfate salts and spherical concretions, both signs of the formation of the rocks under wet conditions. Squyres noted that he had expected to see just basalt below the top salty layer, but instead there is salt as far down as the rover instruments have been able to see so far. "There is an awful lot of salt down there, much more than initially expected," said Squyres. "That means there was a lot more water there than believed."

He hypothesized that "we are seeing large amounts of salt that were deposited and mixed by the wind. We are looking for tell-tale signs of wind action."