As NASA scientists pored over striking new photos from Mars revealing finely layered formations of ancient bedrock, engineers labored on Tuesday to diagnose problems with two robotic rovers on opposite sides of the red planet.  

Besides a serious malfunction that has idled the first rover, Spirit, since last Wednesday, mission controllers at NASA's Jet Propulsion Laboratory said they are now contending with a power drain on Spirit's newly arrived twin, Opportunity.

Mission manager Jim Erickson told reporters the power loss appeared to be from one of the craft's heating units that keeps turning itself on and running overnight without receiving commands from NASA to do so.

While engineers do not believe the faulty thermostat will overheat the vehicle, the long-term consequences of the glitch and whether it can be fixed are not yet known, Erickson said.

"I'd like to have a little more information on what we're seeing from the vehicle before we make any judgments there," he said.

Otherwise, the rover was "in pretty good shape" as a new martian day, its fourth, dawned over Opportunity's landing site on a wide, flat plain known as the Meridiani Planum.

The area is of interest to scientists because it is believed to contain large deposits of an iron-bearing crystalline mineral called hematite, which on Earth usually forms in the presence of liquid water.

Both Opportunity and Spirit are equipped with a mobile laboratory of geologic tools designed to search for evidence that the barren martian surface was once wetter, and possibly more hospitable to life, than it is now.

Seeing rock layers

The first three-dimensional, panoramic images beamed back from Opportunity showed an intriguing outcrop of exposed bedrock "in exquisite detail," said principal science investigator Steve Squyres of Cornell University.

The nearby bedrock formation, the first ever found on Mars, consists of fine layers, some no thicker than a finger, that are believed to be billions of years old, Squyres said. Also visible is a feature believed to be cross-bedding, in which the mineral layers lie at angles to the horizontal stack, which can form from cyclical patterns of sediments that build up, then partially erode away, then rebuild again.

"It's going to be fascinating beyond words to get up close" to the bedrock, he said. "We're going to drive up to this rock outcropping and beat on it with everything we've got."

Andrew Knoll, a science team leader from Harvard University, said the rock layers either originated from ash spewed by volcanic activity early in Mars' history, or from sediments deposited there by wind or water. Closer examination should answer those questions, he said.

Opportunity's "high-gain" antenna, the one used for high-speed communications directly with Earth, has been moved into position, and engineers plan to lift the folded rover off its belly during the day and stretch out its front wheels, Erickson said.

He added that Opportunity was probably still a week away from being ready to roll off its landing platform and onto the floor of the small, shallow crater where the spacecraft is resting. Spirit rolled onto the martian surface 12 days after it landed January 3 in a giant, Connecticut-sized basin known as Gusev Crater, half a planet away.

Spirit still idle

JPL controllers say they are proceeding cautiously with Opportunity in hopes of avoiding a repeat of the difficulties that have left Spirit crippled since last week.

Mission manager Jennifer Trosper said engineers are exploring several scenarios for what may have caused problems with Spirit's onboard computer memory, including an overload from the buildup of data files during the spacecraft's eight-month voyage to Mars.

Another possibility is a burst of charged particles from a solar flare that could have bombarded the rover at a vulnerable point during its communications with Earth.

Project managers have said they hope to understand and overcome their problems with Spirit and return the rover to service in the next few weeks.

(China Daily January 29, 2004)