Sojourner Rover

Mars
Pathfinder
Mission

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Mars
Pathfinder

Robots on Mars

After the Mars Pathfinder landed in July, 1997 it began a successful mission exploring Mars with on-board instruments and the robot Sojourner rover. The rover, named Sojourner after American civil rights crusader Sojourner Truth, is 65 centimeters (2 feet) long, 48 centimeters (1.5 feet) wide and 30 centimeters (1 foot) tall. On Earth it weighed 10.5 kilograms (23 pounds) but on Mars weighed only 4 kilograms (8.8 pounds) due to the difference in the size of the two planets. The robot carried a device called an Alpha Proton X-ray Spectrometer used to test soil and rock samples to determine what minerals were present.

In the descriptions below from NASA/JPL the Sol dates refer to Mars "days" to distinguish them from Earth days.

Sojourner rover tests the rock called Moe This color image (left) shows the Sojourner rover's Alpha Proton X-ray Spectrometer (APXS) deployed against the rock "Moe" on the morning of Sol 65. The rock behind the rover is "Half Dome", which was previously measured by the APXS.
(Image Description by NASA/JPL)

Half Dome Rock (right)
"This image of the rock "Half Dome" was taken by the Sojourner rover's left front camera on Sol 71 (September 14). Pits, linear textures, and pronounced topography on the rock are clearly visible."
(Image Description by NASA/JPL)

Half Dome rock is about the size of the rover. In the lower left corner a rover track is visible.

Sojourner rover on the rock called Wedge Wedge (left)
"This image taken on Sol 44 shows the Sojourner rover with its left front and middle wheels perched on the rock "Wedge". The rover's Alpha Proton X-ray Spectrometer (APXS) is the cylindrical object extending from the back of the rover."
(Image Description by NASA/JPL)

Using the Alpha Proton X-ray Spectrometer (APXS), it takes about 10 hours for a full study of a sample to determine its composition. The APXS bombards the sample with alpha particle radiation. Alpha particles are the nucleus of a Helium atom. The studies showed that Mars and Earth are made up of similar material, such as andesite from volcanic activity and basaltic igneous rock.

The image at right is the rover's view of the lander showing the deflated airbags, ramps and solar panels. The dark circle is the NASA logo on the side of the lander. Click image or here for a diagram of the lander and its instruments.

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Mars Pathfinder
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Geology Terms

Here are some basic terms used on this page. Find more geology terms in the Glossary.

Andesite: Volcanic igneous rock related to granite.
Ares Vallis: Area of Mars where the Mars Pathfinder and Sojourner Rover landed.
Basalt: Volcanic rock caused by partial melting of the Earth's crust.
Floodplain: A smooth plain covered by deposits of sand, gravel and rocks from floods. Sharp-edged rocks have only been carried by floodwaters a short distance while smooth, rounded rocks have traveled long distances.
Granite: Coarse-grained igneous rock usually without obvious bands or markings.
Igneous Rock: Rock that has been melted, cooled and become solid.
Metamorphic Rock: Rocks that have changed form through high pressure and heat. Examples are marble, gneiss and slate.
Regolith: Weathered rocks, gravel, soil and such that covers bedrock.
Sedimentary Rock: Rock formed by pressure and accumulation, e.g., lakebeds changed into rock form loose sand, silt and organic materials.
Volcano: A vent at the surface where magma, gas and steam erupt. Also, the landform constructed by volcanic material.

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