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Pathfinder Images Show Martian Sunset
By DIANE AINSWORTH

     Recent images taken by taken by the Imager for Mars 
Pathfinder (IMP) instrument aboard the Carl Sagan Memorial 
Station show the Martian sunrise and sunset, with water ice 
clouds floating through the atmosphere.
     The collection of photographs included one portion of the 
super panorama view looking to the north-northeast from the 
Pathfinder 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 
seven weeks, said Pathfinder Project Scientist Dr. Matthew 
Golombek. 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 remained in roughly the same range they 
have been in since the start of the mission. The low on Aug. 27 
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 Aug. 
26 (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 (six to nine 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 Aug. 28 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 of the rock nicknamed Shark, the 
rover moved toward another rock called Half Dome, but climbed too 
high up on the rock and automatically shut itself off.
     On Aug. 28, the rover team instructed 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. 
     Images and comprehensive updates on Pathfinder science 
results are available on the Internet at 
http://mpfwww.jpl.nasa.gov or via JPL's Web site at 
http://www.jpl. nasa.gov/marsnews/. Daily audio updates are also 
available by calling (800) 391-6654. 

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