ARES VALLIS, MARS—While children on Earth scoured their local toy stores for the Mattel "Hot Wheels" models of Mars Pathfinder and rover Sojourner, the Pathfinder team at the Jet Propulsion Laboratory in Pasadena, Calif., settled down to the business of "doing science" on the Red Planet. To accomplish "science" this week, Sojourner was commanded to drive from Yogi rock through the granular patch known as the Cabbage Patch and on to Scooby Doo.
The Mars rocks typically get names that indicate something about their shape—for example, Yogi bears a profile resembling that of a cartoon character of the same name.
Yogi was the center of attention during the second week on Mars (Figure 1). On July 15, the team announced the alpha proton X ray spectrometer (APXS) results for this meter-sized boulder. Yogi has the composition of a basalt. Yogi's composition was not a big surprise. Mars has shield volcanoes and volcanic plains formed by flood lavas, similar to the Columbia Plateau in the state of Washington. But Yogi is the first Mars rock confirmed to have a basaltic composition. Yogi is different from the rock examined during Week 1, Barnacle Bill, which has the chemistry of an andesite.
Fig. 1. Sojourner backing up to Yogi (silhouette at far right). Analysis of this meter-sized boulder indicated a basaltic composition.
The Ares Vallis channel was selected for the Pathfinder landing because it was hoped that the flood waters had transported a wide variety of rock types to the site. Sojourner can only explore an area within a few tens of meters of the lander, so easy access to many different rocks is the key to scientific success of the mission. By the end of the second week, Sojourner had driven across the Cabbage Patch, and placed the APXS on the white rock, Scooby Doo. It's composition was planned to be announced at a press conference during Week 3.
Meanwhile, weather on Mars (Figure 2) continued to be the object of much discussion. Prior to landing, some investigators were predicting a relatively dust-free, blue sky. According to Todd Clancy of the Space Science Institute in Boulder, Colo., Mars' climate has been much cooler and less dusty over the past several years than it was during the Viking missions in the 1970s. The pink, dusty sky seen by Pathfinder was a surprise—it didn't fit the predictions based on the observations made by Clancy and his colleagues. The Hubble Space Telescope helped solve the mystery. A dust storm near the north polar ice cap of Mars developed and decayed rather rapidly sometime between July 2 and 10. A small amount of dust was apparently transported to the south of this storm, so that it drifted over the landing site just on time for the July 4th landing. Another dust storm that occurred in late June in Valles Marineris (south of the landing site) probably also contributed dust to the skies over Ares Vallis.
Temperatures on Mars continued to range from between about -80°C and -1°C throughout Week 2. Winds were light and the direction from which they came varied throughout each day. Plans for Week 3 include moving Sojourner back toward the southern side of the lander, to investigate rocks in the neighborhood of "Flat Top" and "Shark."—Ken Edgett, Arizona State University, Tempe
Back to Science for Everyone
