Pathfinder Reaches Out For Life Beyond Earth Space Probe To Land On Mars On Friday, May Be First Step Toward Human Exploration

We humans are taking a giant step this week in our quest for signs of life beyond Earth.

Two-and-a-half hours before the sun rises on Mars on Friday (about 10 a.m. PDT), an American rocket ship swathed in 16 balloons is to land with a series of humongous bounces in a rock-strewn flood plain near the Martian equator.

After rolling to a stop, the spaceship Pathfinder is to open like the petals of a flower to let a little roving robot, tagged Sojourner, trundle down a ramp and start exploring the ruddy surface of the Red Planet - an object of awe and speculation since the dawn of mankind.

“This is a new way of landing a spacecraft on a planet,” said Brian Muirhead, flight systems manager at the National Aeronautics and Space Administration’s Jet Propulsion Laboratory in Pasadena, Calif. “Frankly, we’ll be very surprised if everything goes just right.”

But if it does, Pathfinder, about four hours after landing, will pop up an antenna and radio back the first close-up pictures of Mars since the Viking landings 21 years ago. Live television pictures are expected that evening and daily through the first week of the mission.

In advance of the landing, the Hubble Space Telescope is checking the Martian weather. It is expected to be unusually cold, cloudy and windy.

As its name implies, Pathfinder’s purpose is to open an era of scientific exploration that NASA hopes will lead to a human expedition to Mars early in next century. The $250 million mission - cheap by NASA standards - is the first of a dozen voyages planned over the next eight years by the United States, Russia, Europe and Japan.

The ultimate goal, according to NASA Administrator Dan Goldin, is to find out if living organisms once existed - or still exist - on or under the frosty surface of Mars, the heavenly body most like Earth and most likely to support life.

Although the Viking missions found no signs of life in 1976, they sent back thousands of pictures revealing that Mars once was a warm and watery planet, much like Earth when life took hold here some 4 billion years ago.

“Mars fascinates us,” Goldin told a scientific symposium. “It’s not so close to the sun that its water boiled away, and it’s not so far away that its water froze.”

On this visit, NASA officials don’t expect to find evidence of primitive Martian life - past or present - although they would be delighted if they did.

Instead, Pathfinder and its 23-pound roving sidekick will check out what scientists believe is a likely site for finding rocks like the 4-billion-year-old Martian meteorite that was picked up in Antarctica in 1984.

Last August, after years of intense study, some researchers claimed the meteorite contained what looked like ancient fossils of micro-organisms resembling the strange bacteria recently found at the bottom of the ocean and deep underground on Earth.

Other scientists dispute the meteorite evidence, however. A definitive answer probably must wait until a future spacecraft brings back Martian samples to study in terrestrial laboratories - a mission planned for 2005.

Pathfinder’s landing site, Ares Vallis, was chosen because it contains a treasure-trove of rocks washed down from the Martian highlands during what scientists believe was a catastrophic flood more than 3 billion years ago.

The site “drains a region of ancient, heavily cratered terrain that dates back to early Martian history,” said Matthew Golombek, the chief project scientist. “By examining rocks in this region, Pathfinder should tell scientists about the early environment on Mars, which is important in evaluating the possibility that life could have begun there.”

Another important goal of Pathfinder is to learn how to operate robots safely and successfully on Mars, a necessity for further exploration.

“We need robots that can see, hear, smell, feel and be trained,” said Goldin.

Sojourner, for example, has a small on-board computer to control its six wheels, steer it over and around obstacles and aim its three cameras. It has to be somewhat self-reliant because it takes at least 20 minutes to relay a radio message from Mars to Pasadena and back.

Donna Shirley, a Mars program manager, said the oven-sized rover is “about as smart as a bug.”

Here is how NASA expects the mission to unfold:

At dawn today, after a voyage of 308 million miles from Cape Kennedy, Fla., Pathfinder was still 1.3 million miles from Mars, traveling at about 12,000 miles per hour. It is supposed to enter the Martian atmosphere at 10:02 a.m. PDT on Friday at a speed of 16,600 miles per hour.

The next 4-1/2 minutes are critical. Starting at a height of about six miles above the surface, the spacecraft is to deploy a parachute, inflate its air bags and fire small rockets to cut its speed.

Striking ground at about 50 mph, the ungainly beach ball will bounce as high as a 10-story building and tumble and roll for as long as several minutes before coming to a stop.

The air bags automatically will deflate, and three large metal petals that form the shell of the spacecraft will unfold. During the Martian day, the petals will serve a solar panels to provide power.

Pathfinder will be unable to send messages to Earth until the sun rises, about 2 p.m. PDT, but a low-powered radio carrier wave will let controllers know when the craft has landed. The first detailed transmission is expected about 5 p.m. PDT, showing a black-and-white image of a part of the spacecraft and one of its air bags. The first color pictures of the region around the rover will follow soon after.

Sojourner will remain parked on one of Pathfinder’s petals for up to three days after the landing while controllers study photographs to decide if conditions are safe for it to move.

If so, it will spend the next seven Martian days creeping about the nearby area at a pace of about 120 feet per hour, using its own solar panel and batteries for power. At first, it won’t be allowed to venture beyond 50 yards, but its travels could be extended as long as its power and electronics last.

The mother ship itself is supposed to operate for at least 30 days - possibly up to a year - taking color pictures of the terrain and atmosphere and collecting meteorological data.

As it makes its rounds, the rover will carry a tool kit of miniature scientific instruments, including cameras and an X-ray spectrometer to determine the chemical composition of rocks and soil.

It can do clever tricks such as determining the nature of the soil by measuring how deep its wheels sink.

Pathfinder also carries stereoscopic cameras and instruments to measure wind speed and atmospheric conditions.

Starting in September, Pathfinder and its partner, if they are still awake, will be joined by a second American spaceship, the Mars Global Surveyor, which was launched last November, a month before Pathfinder, but is taking a longer route to get there.

Surveyor won’t land on Mars but will spend two years in orbit making a detailed map of the planet, including its enormous volcanoes, vast canyons and network of winding river channels. It will be able to photograph objects as small as automobiles, including the abandoned Viking landers and Pathfinder.

As with Pathfinder, Surveyor’s goal is to prepare the way for a possible human expedition to Mars and to help identify the best spots to search for signs of extraterrestrial life.