Wednesday, August 29, 2007

Results from Mars Pathfinder

Credit: NASA

Although Mars Pathfinder was expected to operate any time between a week to a month, it eventually lasted for almost three months. The final contact with Pathfinder was at 10:23 UTC on September 27, 1997, on sol 83. Although mission planners tried to restore contact during the following five months, the mission was terminated on March 10, 1998. The Lander's silver-zinc battery was only capable of being recharged about 40 times; as a consequence, after about sol 40, the battery was not able to keep the Lander warm at night. The exact reason for the final failure of the Lander is not certain, but it was probably due to an electronics failure due to the very cold night-time temperatures that were experienced in the final weeks of the mission. After sol 92, the automatic backup procedures should have instructed Sojourner to return to the Lander and circle it while attempting to re-establish communications. This behavior would have continued until hardware failure.

Mars Pathfinder returned 16,500 images from the lander and 550 images from the rover, as well as more than 15 chemical analyses of rocks and soil, plus extensive data on winds and other weather factors. Among the scientific findings were:
  • The APXS analysis of "Barnacle Bill" showed its origin to be consistent with the Martian meteorites. The rock is about 60% felsic, 40% mafic, roughly 1/3 quartz, 1/3 feldspar, and 1/3 orthopyroxene. This would classify it as an andesite (a type of rock found in the Andes mountain) 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. "Barnacle Bill" could also be a mixture of basalt or granite mixed in a sedimentary rock or impact melt. However, results from spot reflectance spectra compared with spectral results from fresh volcanic earth rocks strengthen the case that it is a volcanic andesite.
  • Preliminary analysis of the APXS data returned for "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" appears to be a sedimentary rock composed primarily of compacted soil. The APXS analysis of Scooby-Doo shows only minor differences from the local soils analyzed.
  • Images 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.
  • The analysis of soil samples by the APXS shows a very close match to soils examined by the Viking Landers. There are some differences, however. Soils at the Mars Pathfinder site generally have higher aluminum and magnesium, and lower iron, chlorine, and sulfur than those studied by Viking.
  • Preliminary analysis indicates the possibility that all Martian dust is at least slightly magnetic. The dust is believed to contain maghemite, a strongly magnetic mineral formed in environments of scarce oxygen.
  • Temperatures measured from the top of the 1 meter mast on Mars Pathfinder varied from daily highs of about 260 K (+8 F) to lows of 196 K (-107 F).
  • Imaging of the sky and the sun at different elevations above the horizon showed the atmosphere to be moderately dusty, consistent with what was seen by the Viking Landers. The optical depth indicates that about 35% of the direct sunlight at noon is scattered or absorbed by dust. Visibility tends to be about 30 km. The dust appears to be spread vertically high into the atmosphere and is globally distributed. The sky is hazy and salmon-colored, as it was for Viking.
  • Extensive water-ice clouds have been imaged in the pre-dawn hours by the Lander camera. The clouds moved from the NE at about 7 meters per second (15 mph) and disappeared right around sunrise. The clouds are thought to consist of frozen water condensed around dust particles.

    The above photo was taken by the left-side camera on the Mars Pathfinder Lander. The Lander carried a stereoscopic camera on an extendable pole that allowed "3-D" images to be taken. The photo shows the "Rock Garden" in the foreground and "Twin Peaks" in the background. The "Twin Peaks" are modest-sized hills to the southwest of the Mars Pathfinder landing site. The peaks were discovered on the first panoramic photos taken by Pathfinder's camera on July 4, 1997, and subsequently identified in Viking Orbiter images taken over 20 years ago. The peaks are approximately 30-35 meters (100 feet) tall. North Twin is approximately 860 meters (2,800 feet) from the lander, and South Twin is about a kilometer away (3,300 feet). The scene includes bouldery ridges and swales or "hummocks" of flood debris that range from a few tens of meters away from the lander to the distance of the South Twin Peak.
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