The Mars Pathfinder Mission; July 1998; Scientific American Magazine; by Golombek; 10 Page(s)

"Rocks, rocks, look at those rocks," I exclaimed to everyone in the Mars Pathfinder control room at about 4:30 P.M. on July 4, 1997. The Pathfinder lander was sending back its first images of the surface of Mars, and everyone was focused on the television screens. We had gone to Mars to look at rocks, but no one knew for sure whether we would find any, because the landing site had been selected using orbital images with a resolution of roughly a kilometer. Pathfinder could have landed on a flat, rock-free plain. The first radio downlink indicated that the lander was nearly horizontal, which was worrisome for those of us interested in rocks, as most expected that a rocky surface would result in a tilted lander. The very first images were of the lander so that we could ascertain its condition, and it was not until a few tense minutes later that the first pictures of the surface showed a rocky plain--exactly as we had hoped and planned for.

Why did we want rocks? Every rock carries the history of its formation locked in its minerals, so we hoped the rocks would tell us about the early Martian environment. The two-part Pathfinder payload, consisting of a main lander with a multispectral camera and a mobile rover with a chemical analyzer, was suited to looking at rocks. Although it could not identify the minerals directly--its analyzer could measure only their constituent chemical elements--our plan was to identify them indirectly based on the elemental composition and the shapes, textures and colors of the rocks. By landing Pathfinder at the mouth of a giant channel where a huge volume of water once flowed briefly, we sought rocks that had washed down from the ancient, heavily cratered highlands. Such rocks could offer clues to the early climate of Mars and to whether conditions were once conducive to the development of life.