Rover Exploring Mars Under Its Own Guidance

The rover Sojourner set a new land distance record on Mars last week, navigating almost 20 feet over silty, salmon-colored sand and around jagged rocks without help from controllers, scientists at the Jet Propulsion Laboratory said Thursday.

The Sojourner’s solo drive marks the beginning of a new, more adventurous phase of exploration for NASA’s one-foot-high geologist. “In the last seven days or so, it’s been much more on its own,” said rover scientist Henry Stone, adding that Sojourner’s proud scientists were thrilled with its new independence. So, apparently, was Sojourner, said project scientist Matthew Golombek. “It did a wheelie, it was so excited.”

Researchers at a press briefing also unveiled images of swirling, rose-colored ice clouds in the predawn Martian skies, and a deep red sunset that fanned out in an unexplained pattern.

The weather station on the mother ship Pathfinder picked up temperature differences so extreme that, at midday, a person standing on Mars could comfortably go barefoot (about 70 degrees at ground level), yet have to wear a wool hat (only about 15 degrees) at an altitude of five feet.

The Imager for Mars Pathfinder--the camera known as IMP--sighted a strange white spot on a nearby hillside, which researchers concluded was probably the back shell ejected from the Pathfinder seconds before touch down on Mars. “We think we’ve found the first piece of litter on Mars,” said participating scientist Michael Malin. “And it’s our own.”

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Sojourner’s recent travels have taken it through an area called Cabbage Patch, between two rocks called Calvin and Hobbes, and past a small mountain scientists have dubbed the Mini-Matterhorn. Using its own sensors, it found a rock called Souffle, then turned around a took a snapshot of its mother ship, Pathfinder, sitting in a pile of deflated air bags resembling rumpled sheets on an unmade bed.

Pathfinder plans to take Sunday and Monday off to recharge its batteries, not gathering data or transmitting it to Earth. On Tuesday, Sojourner will make its way to Mermaid Dune, stopping to make chemical analysis of the unusually dark soil. Then it will head for Book Shelf, and the Rock Garden, where it will “go after Shark, Half Dome, Stimpy and Wedge,” Golombek said. All are large, dark rocks of special interest to researchers because they appear to be bare of the ubiquitous pink Martian dust.

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Eventually, Sojourner will try to make a complete 360-degree clockwise circumnavigation of the Pathfinder lander site: Magellan on Mars.

During its early weeks on Mars, controllers sent Sojourner explicit instructions: Drive forward so many feet. Turn right. Drive forward again. Last week it got license to navigate on its own.

Now, controllers only give it a destination and general directions--for example, the headings for Souffle. The rover sets out in that direction, avoiding rough terrain by sending out laser beams that reflect off the rocks and soils. If the rover’s stereo cameras detect a rock too large to crawl over, Sojourner turns to go around it.

At the same time, motion sensors embedded in the rover’s wheels and suspension systems warn Sojourner if it’s tilted precariously, or if one of its wheels is spinning. Last week, a current overload in one of the wheels suggested to controllers that a Sojourner may have picked up a pebble; they told it to drive backward to free the rock.

During the rover’s sojourns, Pathfinder’s IMP camera has been sending home postcard quality scenic views of fluffy, swirling ice clouds that look like hot pink lamb’s wool. Although researchers knew that frozen water made up most of Mars’ northern polar cap, and water vapor lurked in its tenuous atmosphere, they had never seen clouds in such detail before. “We were hoping to see these kind of clouds,” said Mark Lemmon of the University of Arizona, an IMP team member.

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Still, ice clouds do not mean there’s any liquid water on Mars, which would be necessary for life. “It will definitely not rain on Mars,” said Robert Haberle of NASA Ames Research Center.

Unfortunately, when IMP tried to image Earth, our planet hid behind a Martian cloud bank, blocking the view. Pathfinder will try again soon, however, scientists said.

Martian weather turns out to be wildly turbulent on time scales much shorter than expected, according to Haberle. Atmospheric pressure swings up and down much more drastically than it does on Earth, and temperatures can climb 30 to 40 degrees and then plummet again in periods as short as a second.

The variations, said Haberle, are probably caused by extreme turbulence. The turbulence, in turn, is probably the result of the extreme temperature differences recorded between the bottom sensor--close to the surface--and the top sensor, which is several feet up.

The Pathfinder is approaching the end of its planned 30-day mission, which began July 4, when it bounced to the surface in a cocoon of air bags.