PASADENA, Calif. (AP) -- The Sojourner rover became the firstmobile vehicle to roam another planet Sunday, rolling ontothe floury martian soil into a diverse landscape bearingunmistakable signs of ancient water activity, the basicrequirement for life on any planet.
Hours after it rolled down a ramp from the Mars Pathfinderlander, the tiny rover began a new era of exploration of thered planet.
"She is the robotic equivalent of Neil Armstrong on Mars,"rover scientist Henry Moore said proudly. "She's your fieldgeologist, and she wants to thank the people of the United States and all foreign contributors payingfor her."
Mission scientists treat the foot-high Sojourner, which has a 3-D camera and an instrument designedto chemically analyze the martian surface, as if it were alive. Just before 4 p.m., as they woke therover for its first full day on martian soil, they played the theme to the television show "Mad AboutYou" in the control room.
"We have the perfect site, the perfect spacecraft, the perfect instruments and the perfect rover,"said project scientist Matthew Golombek.
On Sunday afternoon, Sojourner sat just beyond the ramp, at the end of a distinct pair of tracks inthe red dust. From studying the tracks, geologists said the surface seemed like a thin dusting offlour over a harder layer.
By day's end, Sojourner was expected to have completed a 90-degree counterclockwise rotation,then backed up a few inches to put its alpha proton X-ray spectrometer in contact with "BarnacleBill," a bumpy rock about the size of the rover.
Already, mission scientists were beginning to do field geology by looking at the landscape in imagestransmitted from 120 million miles away. A light-colored vertical mark on a hillside could be anavalanche gully, said University of Arizona geologist Ron Greeley. Horizontal features on anotherhill could be terraces cut by moving water, horizontal rock layers laid down in a lake or a bathtubringlike feature left along an ancient shoreline.
"These all are indicators of water activity," Greeley said.
Because the search for life on Mars is the central theme of NASA's long-term Mars exploration strategy, much of Pathfinder is dedicated to determining whether water once flowed across the landing site, and if so, for long.
Analysis of its chemical elements would follow to figure out what minerals are in the rock. The ultimate goal -- to understand the geologic history of the landing site -- will take years of scientific wrangling.
"The full story isn't going to emerge in a short period of time, but we really have the tools to do the job now," said Greeley.
Communications with Pathfinder are not continuous because radio signals can't reach the spacecraftwhile it is on the opposite side of Mars from Earth. Because the martian day is slightly longer than24 hours, communications happen roughly on a 12-hour on, 12-hour off schedule.
As the mission continues, the 12-hour on period gets later and later. It now extends from earlyafternoon to a few hours after midnight. A week from now, mission controllers will findthemselves up all night.
Geologists said they couldn't have been happier with the landing site, a mostly flat plain studdedwith rocks and boulders, thought to have washed down from distant highlands in violent floodsbillions of years ago. On the horizon are hills with horizontal colored bands -- the fingerprint ofliquid water.
"We really wanted to see the geologic diversity of Mars, and we have not been disappointed,"Greeley said.
Mars is thought to have had water, a vital component of life, on its surface billions of years ago.That water could have been lost to space, or it could still be on Mars today, frozen undergroundand in the polar caps.
"Mars may even be more water-rich than Earth is. We really don't know," Golombek said.
The site is so varied, with distinctive hills and a small crater less than a mile away, that scientistshave already figured out exactly where the craft is on Mars. When the Viking missions went toMars in 1976, it took a year to figure out where one of the spacecraft landed. The position of theother was never accurately determined.
Scientists presented the first panoramic photograph of the Pathfinder site Saturday, ablack-and-white 360-degree view that can be accessed through Internet sites.
Internet sites were being added as NASA's got swamped. By Sunday morning, those computers hadreceived an estimated 100 million "hits," said Rich Pavlovsky, a programmer helping manage thesite for the Jet Propulsion Laboratory.
It was among the biggest Internet events yet; by comparison the traffic was similar to that on themost popular political sites during the busiest few hours on election night.
The lander's camera mast was extended to full height early Sunday and subsequent photographswere expected to be full-color and more detailed.
Scientists also provided a weather report from Mars. Pathfinder's meteorological equipment washaving some problems but did return noontime conditions from the first two days of the mission.Temperatures hovered around zero degrees Fahrenheit, with light breezes that occasionally causedthem to dip as low as 25-below.
"It's better than what people are used to in the northern United States in the fall and in the winter,"said Peter Smith, a University of Arizona professor who heads the lander camera team.
Mission managers now feel confident that Sojourner will last much longer than its intendedone-week lifetime, and the lander will continue to operate much longer than the month it wassupposed to. The lander's batteries could easily last for months, said flight system manager BrianMuirhead, and theoretically, Sojourner could live forever.
"I think the rover and the lander have a long life together on Mars," Muirhead said.