Robot Explorers: US Unmanned Space Missions: page 22

Artist's rendering of Pathfinder dropping onto the surface of Mars.

Pathfinder's scientific objectives included atmospheric entry science, long-range and close-up surface imaging, with the general objective being to characterize the Martian environment for further exploration. The spacecraft entered the Martian atmosphere without going into orbit around the planet and landed on Mars with the aid of parachutes, rockets and airbags, taking atmospheric measurements on the way down. Prior to landing, the spacecraft was enclosed by three triangular solar panels (petals), which unfolded onto the ground after touchdown.

The rover "Sojourner" was a six-wheeled vehicle which was controlled by an Earth-based operator, who navigated using images obtained by both the rover and lander systems. The primary objectives were scheduled for the first seven sols (1 sol = 1 Martian day = ~24.7 hours), all within about 10 meters of the lander. The extended mission included more analyses of nearby rock and soil and more tests of the rover capabilities.

This image of Sojourner was taken by the camera on the Pathfinder lander on Sol 30.

Below is a full-color panorama of the landing site from the Mars Pathfinder camera. Images such as this one from Pathfinder are consistent with the earlier results from Viking Orbiter images that Ares Vallis was the site of a massive flood about one to three billion years ago, and with measurements by the Viking Landers showing large quantities of iron oxides in the soil.

Sojourner was outfitted with an instrument that allowed it to determine the chemical content of Martian rocks and soil. Analysis of the rock "Barnacle Bill" showed its origin to be consistent with the Martian meteorites. The rock was found to be about 1/3 quartz, 1/3 feldspar, and 1/3 orthopyroxene. This would classify it as an andesite if it is an igneous rock, a highly differentiated quartz-rich rock compared to the Martian meteorites, which are classified as basalts. This would indicate that Mars has been more thermally active in its past than was previously thought, producing at least some highly remelted and differentiated rocks.

Preliminary analysis of the rock "Yogi" suggested it was very different from Barnacle Bill. If Yogi is of volcanic origin, it appeared to be basalt, a primitive, unprocessed rock type. However, a thin covering of dust on the rock indicates there is probably a soil component mixed in these measurements. Rough estimates have been made of the contribution of the soil component. Subtracting this out gives a composition of Yogi similar to that of Barnacle Bill.

The rock "Scooby-Doo" appeared to be a sedimentary rock composed primarily of compacted soil.

The analysis of soil samples showed a very close match to soils examined by the Viking Landers, with a few differences. Soils at the Mars Pathfinder site were found generally to have higher aluminum and magnesium, and lower iron, chlorine, and sulfur than those studied by Viking.

The Pathfinder lander and Sojourner rover operated until communication was lost for unknown reasons on September 27, 1997.

For more information on Pathfinder and Sojourner visit  http://marsprogram.jpl.nasa.gov/MPF/

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Copyright ©2004 Colleen Gino

Images and content courtesy JPL and NASA.