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Pathfinder Blazes a Trail to Mars
by Damond Benningfield
For the first time since the Viking missions of the 1970s, an American spacecraft is set to land on Mars. The small, high-risk Mars Pathfinder will drop onto an ancient Martian flood plain on July 4, beginning up to a year of scientific studies. It will photograph its surroundings, monitor the weather, and deploy a small rover to scoot around the landing site and determine the composition of Martian rocks.
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Pathfinder will descend directly to the Martian surface without orbiting. A parachute and airbags will cushion its landing. (NASA)
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Pathfinder will land at the mouth of Ares Vallis ("Valley of Mars"), a flood plain created when a wall of water gushed from an underground reservoir in the distant past. The torrent was equivalent to all the water in the Great Lakes rushing to the Gulf of Mexico in just a few weeks. The flood sliced deep channels and carved teardrop-shaped islands. It gathered rocks and soil representing billions of years of Martian history and deposited them at the mouth of Ares Vallis.
Pathfinder is primarily a technology demonstration project. It was built on a limited budget, so designers relied on risky, unproven techniques for landing the craft.
Unlike the Vikings, which entered orbit before landing, Pathfinder will drop directly to the surface.
Pathfinder will encounter the first wisps of Martian air about 78 miles (125 km) above the surface, traveling at about 17,000 miles an hour (27,000 kph). Friction with the thin atmosphere will generate intense heat, surrounding Pathfinder in a fireball. A blunt heat shield will protect the craft.
Several miles above the surface, the heat shield will fall away and a parachute will open to slow Pathfinder even more. A few minutes later, powerful rocket motors will fire to slow Pathfinder to a crawl. The parachute will then cut away and Pathfinder -- protected by a cocoon of airbags -- will drop the final 40 to 65 feet (12 to 20 meters), bouncing several times before coming to rest. It will be a few hours before dawn at the landing site.
Shortly after touchdown, Pathfinder will unfold three electricity-producing solar panels, scan its surroundings with stereoscopic cameras, and switch on a small weather station.
A few hours later, scientists on Earth will map a trail for Pathfinder's rover, Sojourner, which is named for nineteenth-century abolitionist and women's rights advocate Sojourner Truth.
Sojourner will travel up to a few hundred yards from the lander. Each night, the rover will park beside a different rock and measure its composition. Its findings will reveal how the rocks formed -- whether they came from volcanoes, for example, or from sediments at the bottom of a lake. Such information will tell scientists whether conditions when the rocks formed were favorable for the formation of life.
Even if Pathfinder and Sojourner are surrounded by Martian fossils, though, neither craft is likely to detect them. While the Vikings looked for signs of life on Mars, Pathfinder isn't equipped with such complex instruments. Scientists must wait for future missions to return rock and soil samples to Earth to determine if anything lives on Mars now, or lived there in the past.
Mars Pathfinder is the second of NASA's "Discovery" probes -- innovative missions that must be built and launched within three years for no more than $150 million. The first Discovery mission, the Near Earth Asteroid Rendezvous, was launched in February 1996. The third, Lunar Prospector, is scheduled for launch in October.
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