Pathfinder's Port of Call
When Pathfinder touched down on Mars it faced a rock-strewn and barren landscape. The landing site was in a region called Chryse Planitia, which means Plain of Gold. But the surface is actually colored by the red iron oxide dust found everywhere on Mars. Chryse Planitia is a wind-whipped flood plain, thought to have been formed when massive flows of water, enough to fill all five of Earth's Great Lakes, rushed over the northern lowlands a few billion years ago.
The target location was the mouth of Mars Valley (Ares Vallis), an ancientriverbed north of the Martian equator. (Vallis means "valley" in Latin.) It lies 850 kilometers (530 miles) southeast of the spot where the Viking 1 Lander touched down in 1976.
Why It Was Chosen
The landing site was chosen after consultation with more than 60 scientists from the United States and Europe. Information gained from the Viking 1 and 2 missions was used to get the lay of the land. Several other possible sites were considered before this one was selected. A number of factors influenced the decision.
The spot had to suit the needs of both the lander and Sojourner, the microrover vehicle that will be examining samples and sending information back to Earth. Shortly after Pathfinder entered the thin Martian atmosphere, a huge descent parachute unfurled to slow it down. The target landing area had to be in a region of low elevation. That's because the lower the elevation, the more time the open parachute had to reduce the speed of the lander. Furthermore, the lower the elevation, the denser the atmosphere; and the denser the atmosphere, the more the parachute will slow the lander.
The fact that both lander and rover are solar powered was another important consideration. They require maximum sunlight to operate efficiently. The position of the Sun in July 1997 was directly over 15 degrees N. latitude. The closest low-elevation, flat area lies on Chryse Planitia.
Finally, the mouth of Mars Valley was ideal because it is a sort of "grab bag" location, according to Pathfinder Project Scientist Matthew Golombeck. Scientists expected to find a large and representative sampling of rocks and soil, all within Sojourner's reach, and they did. Because the material examined had been washed down the valley by floods originating in the northern highlands, it was not possible to determine the exact origin of the samples. Nonetheless, it was the best way to ensure that a wide variety of specimens could be found within the limited reach of the slow-moving Sojourner.
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