Sojourner

Credit: NASA

On July 4, 1997, Mars Pathfinder landed on Mars using a combination of an entry capsule, a parachute, solid rockets, and large airbags. About 21.5 meters above the surface of the planet, the lander and rover, protected by a 5.2-meter "bubble" of airbags, detached from the parachute and bounced onto the surface of the planet. The lander and rover bounced a total of 15 times (the first bounce went up 12 meters into the air), rolling approximately a kilometer from the initial impact site. The lander deflated the airbags, then opened up three "petals" that surrounded the rover, the petals being covered with solar panels to generate electricity. Ninety-eight minutes after landing, Pathfinder began signaling Earth with the data it had accumulated during the descent and landing.

The heart of the mission was the tiny rover, Sojourner, named after the American abolitionist and women's rights activist Sojourner Truth (1797-1883). Sojourner was very small, measuring 65 cm long, 48 cm wide, 30 cm tall, and weighing 10.6 kg. (In comparison, the Mars Exploration Rovers Spirit and Opportunity are both 1.6 meters long, 2.3 meters wide, 1.5 meters tall, and weigh 180 kg.)

While the Mars Pathfinder mission was primarily concerned with engineering and budgetary hurdles (namely, proving the "faster, better and cheaper" program by sending a simple system to another planet at 20% of the cost of the Viking missions), the lander and Sojourner did carry a number of scientific instruments. The lander carried a stereoscopic camera on an extendable pole, plus a meteorological station that measured air pressures, temperatures, and wind speeds and directions. Sojourner carried an Alpha Proton X-ray Spectrometer (APXS) that was used to analyze the components of the rocks and soil. The rover also had three cameras, two black and white and one for color images, plus a number of other experiments.

In the above image, Sojourner is taking Alpha Proton X-ray Spectrometer (APXS) measurements of the rock named "Yogi." The image clearly shows the "two-toned" surface of this large rock. The nature of this color difference is not known; however, it might consist of wind-blown dust accumulated on the surface (the rock is leaning into the prevailing wind) or it might be evidence of a break from a larger boulder as it was deposited in the ancient flood that scoured this area.