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Roving Around Mars
by Damond Benningfield
Barnacle Bill rested quietly amid the hills and channels of Ares Vallis for a billion years or more. A great flood had dropped the football-sized rock near the bottom of a shallow depression, where it was disturbed only by the occasional Martian dust storm.
But on July 7 -- three days after Mars Pathfinder bounced to a stop just inches away -- Barnacle Bill became a star. Giggly scientists gave it a catchy name, television networks gave it more air time than Spice Girls and Will Smith combined, and the rock's own secrets gave it a spot in the planetary history books.
Sojourner, the six-wheeled rover that Pathfinder carried to Mars, stuck its nose against the rock and "sniffed" it awhile. It found that Barnacle Bill may have melted and resolidified long ago, like the rocks blasted from volcanoes on Earth. The finding suggests that Mars may be far more complex -- and far more interesting -- than scientists ever suspected. "We have to start from scratch" to explain Barnacle Bill's history, says Nadine Barlow, a planetary geologist at the University of Central Florida.
Pathfinder sniffed out a few other surprises during its early weeks on Mars. It saw a greater variety of rocks and soil than the twin Viking landers of the 1970s, and found that several great floods may have washed across its landing site, not just one.
Perhaps the biggest surprise is that Pathfinder and Sojourner survived their bumpy landing.
Many of Pathfinder's landing systems and techniques were untried. In particular, no spacecraft had ever used airbags to cushion its landing. After a heat shield, a parachute, and retro rockets slowed Pathfinder to a crawl, the craft fell the final 65 feet (21 meters) to the Martian surface, striking at a speed of about 40 miles an hour. Protected by airbags, it bounced 50 feet (15 meters) high the first time, then bounced and rolled about six-tenths of a mile (one km) over the next two and half minutes before finally stopping.
When Pathfinder switched on its cameras, it confirmed that its landing site in Ares Vallis (Mars Valley) is an ancient outflow channel. Between one billion and three billion years ago, a catastrophic flood rattled Ares Vallis; a volume of water equal to the Mediterranean Sea poured through the valley in just a few weeks. The flood carved channels and teardrop-shaped islands, and deposited rocks and boulders that may have been carried from hundreds of miles upstream.
"The site is everything we hoped it would be," said project scientist Matthew Golombeck a few days after the landing. "We are finding more and more surprises as we look in detail at the rocks and terrain."
Pathfinder landed near a ridge that runs from southwest to northeast. Two sharp-peaked hills are visible in the distance, and stereo images from Pathfinder's camera show gently undulating terrain toward the hills. Thin, high-altitude water-ice clouds condense at night but evaporate soon after sunrise.
A small circular depression beside the lander may have contained a last puddle of water from the flood. Rocks around the craft range from pebbles to boulders, and most sit atop the powdery Martian soil as though they were gently dropped into place.
Scientists gave the rocks names that sound like Cartoon Network program listings: Yogi and Boo-Boo, Scooby-Doo, Casper, and Calvin and Hobbes, with Baker's Bench and Souffle thrown in for those who prefer the culinary arts to the animated kind.
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