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Mars Pathfinder Mission Status
August 27, 1997

      Images of the Martian sunrise and sunset, with water ice clouds floating through the atmosphere, were unveiled today at a Mars Pathfinder press briefing, held on Sol 53 of the mission, at NASA's Jet Propulsion Laboratory.

      Today's collection of photographs included one portion of the super panorama view looking to the north-northeast from the Sagan Memorial lander. The super panorama of the landing site, which is being constructed from high resolution color images taken by the Imager for Mars Pathfinder (IMP) instrument, will be comprised of about 3,000 images when it is completed in about eight weeks, said Dr. Matthew Golombek, Pathfinder project scientist at JPL. This mammoth color and stereo data set, which is now about 65 percent finished, will be used to derive high quality topographic maps of the Martian surface and detailed shapes of rocks and other surface features. Scientists will also be able to examine subtle chemical, mineralogical and textural variations in rocks and soils from this panorama.

      Temperatures on Mars today remained in roughly the same temperature range. Today's low was minus 75 degrees Celsius (-103 degrees Fahrenheit) and the high was minus 10 degrees Celsius (14 degrees Fahrenheit). The highest pressure measurements seen yet on Mars were recorded yesterday (Sol 52) at 6.8 millibars, said Dr. Tim Schofield, atmospheric structure/meteorology package team leader at JPL. In addition to temperature and pressure measurements, Pathfinder has observed a total of 12 dust devils, small swirls of dust kicked up by winds blowing down through the canyons in the Ares Vallis landing zone.

      Scientists are finding that Martian temperatures are cooler at higher altitudes (about 80 kilometers or 50 miles) than on the ground. They think that ice clouds forming about 10 kilometers to 15 kilometers (6 to 9 miles) above the surface are responsible for this cooling trend higher in the atmosphere. The clouds are thought to be made of very small ice particles, about one-tenth the size of Martian dust or one-thousandth the thickness of a human hair.

      Dr. Mark Lemmon, a member of the lander camera imaging team at the University of Arizona, noted color variations in some of the sunset pictures. The blue color is not caused by clouds of water ice but by Martian dust in the atmosphere, Lemmon said. The dust absorbs blue light, giving the sky its red color, but it also scatters some of the blue light into areas that looked very blue around the Sun. The blues only show up near sunrise and sunset, when the light has to pass through the largest amount of dust.

      Sojourner, which remains in excellent health, began exploring the Rock Garden yesterday, after spending about a week en route to the region. The Rock Garden is an assemblage of several large boulders and many smaller rocks near the lander. After conducting a chemical analysis yesterday of the rock nicknamed Shark, the rover moved toward another rock called Half Dome today, but climbed too high up on the rock and automatically shut itself off.

      Tomorrow the rover team will instruct the rover to back down the rock and reposition the alpha proton X-ray spectrometer against the side of Half Dome. Chemical analyses of all of the rocks studied so far indicate that at least two types of rocks are present in the Pathfinder landing zone: those with high levels of silicon and those with high levels of sulfur, reported Dr. Tom Economou, co-investigator of the alpha proton X-ray spectrometer team at the University of Chicago.

      Soil mechanics experiments using the rover's wheels and cleats to dig below the surface have revealed different layers of material, Howard Eisen, principal investigator on the soil mechanics technology experiment at JPL, pointed out. Soil surfaces differ near the lander, where the soil contains a mixture of pebbles, fine-grained sand and clods, from regions a bit farther out. There, the surface is covered with a bright drift material, Eisen said. Using the rover's cleats to dig below the surface, scientists have discovered that cloddy material was present underneath the drift.

      After traveling a total of about 80 meters (263 feet) around the landing site, Sojourner will continue to explore the Rock Garden for the next several days, taking as many chemical analyses as possible of the large boulders in the vicinity. After these rocks have been studied, the rover will head back to the ramp on which it exited the lander and study a dust sample that has been accumulating on a magnet, Golombek said. This study may provide new information about magnetic properties that might be present in the Martian soil. Longer range plans for the rover may take it much farther away from the lander, so that it may peer over the rim of what appears to be a shallow riverbed, and photograph a region that cannot be seen by the lander.

      The Earth rose over Mars on Sol 53 at 8:15 p.m. Pacific Daylight Time and the Sun rose at 11:05 p.m. PDT yesterday (Aug. 26). The Earth set this morning at 9:55 a.m. PDT and the Sun set at 11:35 a.m. PDT.

      Images and comprehensive updates on Pathfinder science results are available on the Internet at or via JPL's home page at . Daily audio updates are also available by calling 1-800-391-6654.