Pathfinder at the End of Its Road on Mars

As the little rover Sojourner on Mars continues futile attempts to rouse its stone-cold and silent mother ship, scientists at the Jet Propulsion Laboratory in Pasadena on Tuesday officially bade a reluctant farewell to the Pathfinder mission.

In sharp contrast to the exuberant atmosphere surrounding the landing on Mars just four months ago--cheered on by NASA chief Dan Goldin and Vice President Al Gore--the ending was much more subdued. Tuesday’s expected telephone call from President Clinton never came. “He got distracted,” said project manager Brian Muirhead.

Mission scientists reviewed panoramic images of the Red Planet--taken in the early, heady days of the mission--like proud grandparents passing around graduation pictures. “We come to praise Pathfinder, not to bury her,” Muirhead said.

On Mars, meanwhile, Pathfinder has not sent home any data since Sept. 27, despite the best efforts of the engineers to reestablish communications. Because the spacecraft’s electronic systems haven’t been turning on to warm up the instruments, mission managers fear that Pathfinder has been literally frozen silent. The end could have come in the form of a solder joint that cracked in the cold or a circuit malfunction, according to mission manager Richard Cook.

Without instructions from Pathfinder, the rover continues to follow its built-in contingency plan, which directs Sojourner to head straight toward the center of the mother ship. The rover cannot actually reach the lander, however, because its programmed instructions also tell it never to come nearer than three meters (about 10 feet) from the center, as determined by its on-board sensors. So it stops, moves around the lander for some distance, then tries to reach the center again the next day.

Some speculate that in these attempts to reach Pathfinder, it may have literally dug a circular ditch around the lander.

Where is Sojourner right now? “That’s what I ask every morning,” said rover scientist Jacob Matijevic. “It will wake up each morning and keep trying to get to the center of the lander,” each time being thwarted, he said, by Pathfinder’s virtual barrier. “My own speculation is that it drove up on a rock and is waiting for instructions from home.”

Nevertheless, Muirhead said, “the mission is not over.” He stressed that periodic attempts will still be made to contact the spacecraft and that much work remains analyzing the data already sent. However, he conceded that “the likelihood of hearing from the spacecraft again diminishes with each day.”

Even if Pathfinder never sends another signal to its home planet, it will have left a memorable legacy both in science and in the hearts of the public. Since the moment the air bag-encased Pathfinder bounced down onto the surface of Mars on July 4, the trip to the Red Planet has been as much a sentimental journey as a technical tour de force.

Overloaded Mars Web sites set new records for “hits,” and Mars rover models sold out in toy stores nationwide. “I think we managed to inspire a lot of people,” Muirhead said.

Pathfinder scientists made the rover’s adventures on Mars seem real to people by giving them human qualities, describing the events as “kissing” or “snuggling up to” a rock, “doing a wheelie,” or sending back “her” thanks to the taxpayers who supported her journey. The rover was named after African American civil rights champion Sojourner Truth.

The researchers also brought the surface of Mars to life with spectacular 3-D images and fanciful names for the rocks--many of them namesakes of familiar cartoon characters such as Yogi Bear and Casper the Ghost.

Among the most important scientific highlights, Pathfinder provided ample evidence that the Red Planet was indeed a warm, wet world in ancient times. It very possibly once had standing water that carved smooth, round pebbles and sand grains, and left traces of long-dried puddles and ponds.

Those findings, said mission scientist Matthew Golombek, will help answer the questions propelling NASA’s continuing Mars missions over the next 10 years: “Could life have developed on Mars if water was stable? If not, why not? And if [life did develop], what happened to it?”

The rover Sojourner’s chemical analyses of silica-bearing surface rocks suggested that Mars’ interior was hotter longer than previously thought--warm enough to recook the original basalt into more highly evolved forms such as silica, which were later “burped up” from the depths onto the surface, Golombek said.

Most of all, the rover proved that an independent, mobile robot can get around on Mars, take pictures, analyze rocks, survey the territory, avoid obstacles and navigate on its own. “That marks a transition in our thoughts of what a mobile vehicle on the surface of a planet can actually do,” Matijevic said.

Sojourner has far exceeded its planned one-week “primary” mission, and Pathfinder’s terminal chill-out is pretty much the end its designers had expected. Still, until future Mars missions happen by for a closer look, no one will know exactly how Sojourner and its mother ship spent their final hours.

“The only evidence may be that we’ll see the lander with a little trough around it,” Matijevic said.

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Farewell, Pathfinder

NASA’s dramatic mission to Mars officially came to a close Tuesday after scientists had tried unsuccessfully for a month to communicate with the spacecraft or its tiny rover.

Dec. ’96

MISSION BEGINS: Pathfinder is launched to Mars.

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June

LANDING: Spacecraft bounces safely on the surface of the Red Planet, and sends first pictures.

ROVER VENTURES OUT: Spacecraft’s 22-pound rover, known as Sojourner, begins to explore.

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Sept.

TROUBLE: First communication problems with Earth begin. Soon, Pathfinder’s transmitter is out of commission.

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Nov.

MISSION ENDS: JPL announces end to Pathfinder’s mission, though data analysis will continue for months.