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Mars Pathfinder surpasses expectations 
By DIANE AINSWORTH and MARK WHALEN

     It keeps going and going and going ...
     That familiar slogan associated with the pink Energizer 
Bunny was one of the many ways the Mars Pathfinder rover 
Sojourner was described at a press briefing this week, three 
weeks after the mission's historic July 4 landing in an ancient 
outflow channel known as Ares Vallis.
     In fact, the Mars Pathfinder rover and lander have surpassed 
the flight team's greatest expectations. With a primary lifetime 
of seven days, the rover continues to operate nearly flawlessly, 
traversing short distances to specific rocks each day, making 
measurements of their composition, then turning to head for the 
next rock a few meters away. Although it is hard to predict how 
long the rover will last, the flight team thinks the hearty robot 
could last much longer. 
     Data from the lander camera -- affectionately called the 
"IMP," for Imager for Mars Pathfinder -- and several other 
experiments continue to be returned in record volume. During the 
last week, more than 300 megabits of data were returned, said 
Pathfinder Project Scientist Dr. Matthew Golombek.
     (As a point of reference, 300 megabits is approximately 
equal to 37.5 megabytes, exceeding that of a computer with 32 
megabytes of memory. It's roughly equivalent to more than 18,000 
typewritten pages.)
     Meanwhile, science data are beginning to reveal more about 
weather and dust patterns on Mars, the magnetic characteristics 
of Martian soil and the origin and composition of rocks in Ares 
Vallis. 
     Rover surface operations were officially under way after 
Sojourner safely crawled off its ramp on July 5. Within three 
days of its exit, the rover had placed its spectrometer on 
Barnacle Bill, the first rock ever to be analyzed on the surface 
of another planet.
     The rock turned out to be unusually rich in silicon, which 
puts Barnacle Bill in one of the most common categories of 
volcanic rocks on Earth, known as "andesites," said Dr. Rudolph 
Rieder of Germany's Max Planck Institute for Chemistry, who is 
principal investigator on the Alpha Proton X-Ray Spectrometer 
(APXS) team. This was completely unexpected for Mars, as high 
silica rocks require differentiation beyond that expected in 
primitive planets.
     Weather on Mars has become the topic of another team's 
studies. Using data from the Atmospheric Science 
Instrument/Meteorology Package (ASI/MET), the weather team led by 
Dr. John "Tim" Schofield has reported each day's weather 
forecast. Because it is currently summer in Mars' northern 
hemisphere, the variations are minimal (for Mars). Generally, the 
temperatures are dropping to about -73 degrees Celsius 
(-100 degrees Fahrenheit), while rising to approximately -15 to -13 
degrees Celsius (5 to 8 degrees Fahrenheit) during the day, 
similar to the temperatures recorded by the Viking landers of the 
mid-1970s.  
     "Future astronauts on Mars won't have much to talk about as 
far as weather goes," said Dr. Julio Magalhaes, a member of the 
ASI/MET team from NASA Ames Research Center in Mountain View, 
Calif. "Northern summer in the subtropics on Mars is pretty much 
the same from day to day. Fifty or 60 days from now, we'll start 
to see dramatic changes with fall," said Dr. Jeffrey Barnes of 
Oregon State University, who is a member of the 
atmospheric/meteorological experiment. The winds are fairly weak, 
blowing up to about 26 kilometers per hour (16 mph) during the 
day. However, scientists expect the winds to increase and begin 
kicking up dust as the Martian fall approaches this September.   
     Atmospheric opacity -- or how clear the sky is, according to 
Pathfinder's atmospheric experiment -- showed that Mars is 
moderately dusty up to about 40 kilometers (25 miles) above the 
surface. The dust appears to be uniformly distributed, and is 
expected to rise as Mars approaches its dusty season in the fall, 
Barnes said. The visibility on Mars was estimated to be about 32 
kilometers (20 miles) or more, roughly equivalent to a moderately 
smoggy day in Los Angeles. 
     Worldwide interest in the mission has peaked with all of the 
new science being reported. On July 22, more than 400 million 
hits had been reported on the 20 Pathfinder mirror sites built 
specially for the mission. Kirk Goodall, Mars Pathfinder Web 
engineer, along with David Dubov, Mars Pathfinder Webmaster, 
reported the most hits ever recorded in a day on a Web site -- 46 
million -- which occurred on July 8. 
     "That's more than double the number of hits received in a 
single day during the 1996 Olympic Games in Atlanta," Goodall 
said.
     "The Mars landing has excited and inspired the public like 
very few activities today," Mission Manager Richard Cook noted. 
"It shows the rest of the world that we can achieve a 
technological marvel like this."
     Speaking of technologies, another popular science tool being 
used in this mission is three-dimensional modeling, which 
recreates the surface of Mars based on stereo images of the 
planet's surface. Three-D modeling has been useful in visualizing 
otherwise unnoticed geologic features, such as the overhang on 
the back side of a large boulder named Yogi. Dr. Carol Stoker, a 
participating scientist from Ames, said the images were shipped 
to Ames, where they were processed and later returned to JPL. The 
3-D imagery was also used to measure distances and sizes of 
objects.
     One of the few problems encountered by the flight team so 
far was a communications glitch, which occurred over the July 19-
20 weekend. The problem was associated with ground operations, 
rather than with faulty hardware on the spacecraft, Cook 
explained during a recent briefing.
     Unlike on other deep space missions, the DSN is required to 
reconfigure its equipment and software on a daily basis and to 
establish the communications links only during short periods of 
time when the lander's transmitter is on. By the middle of this 
week, the team felt confident that the problem was fully 
understood and would not interrupt surface operations. 
     Other recent science studies include soil abrasion 
experiments performed by Sojourner's wheel tracks, asking it to 
perform soil abrasion experiments and measuring the material 
properties of the dust and soil by interacting with it by the 
rover. Dr. Henry Moore, a rover scientist with the U.S. 
Geological Survey in Menlo Park, Calif., likened the Martian soil 
to a very fine-grained silt that could be found in Nebraska, 
finer than talcum powder.
     Dr. Peter Smith of the University of Arizona, who is 
principal investigator of the lander camera, described more about 
the Martian landscape, pointing out a shallow riverbed crossing 
through the landing site and rocks in the distance that were 
washed into this outflow channel from the Martian highlands.
     Science activities for July 23 were set to take the rover 
through the "cabbage patch," an area of soil and small rocks in 
between Scooby Doo and the rock named Lamb. The rover will 
conduct a soil experiment, then turn and move toward Lamb. 
Scientists will take measurements of the dark soil near that rock 
before moving on towards the rocks Cradle and Souffle.
     For the latest mission updates, check Pathfinder's Web site 
at http://www.jpl.nasa.gov/marsnews. An audio update on 
Pathfinder's status can be heard by calling (800) 391-6654. 

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