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Mars Pathfinder Results Featured In This Week's Science Magazine

PUBLIC INFORMATION OFFICE
JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
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http://www.jpl.nasa.gov

Contact: Diane Ainsworth                         Dec. 1, 1997

PATHFINDER RESULTS FEATURED IN THIS WEEK'S SCIENCE MAGAZINE

     Based on the first direct measurements ever obtained of 
Martian rocks and terrain, scientists on NASA's Mars Pathfinder 
mission report in this week's Science magazine that the red 
planet may have once been much more like Earth, with liquid water 
streaming through channels and nourishing a much thicker 
atmosphere. 

     Among the more significant discoveries of the Mars 
Pathfinder mission was the identification of possible 
conglomerate rocks, which suggests the presence of running water 
to smooth and round the pebbles and cobbles, and deposit them in 
a sand or clay matrix, says Dr. Matthew Golombek, Mars Pathfinder 
project scientist at NASA's Jet Propulsion Laboratory, Pasadena, 
CA.  This scenario supports the theory that Mars was once warmer 
and wetter. 

     "If you consider all of the evidence we have at Ares Vallis 
-- the rounded pebbles and cobbles and the possible conglomerate, 
the abundant sand- and dust-sized particles and models for their 
origins, in addition to the high silica rocks," Golombek says, 
"it suggests a water-rich planet that may have been more Earth-
like than previously recognized, with a warmer and wetter past in 
which liquid water was stable and the atmosphere was thicker."    

     A panoramic view of Pathfinder's Ares Vallis landing site, 
featured on the cover of the Dec. 5 issue of Science, reveals 
traces of this warmer, wetter past, showing a flood plain covered 
with a variety of rock types, boulders, rounded and semi-rounded 
cobbles and pebbles.  These rocks and pebbles are thought to have 
been swept down and deposited by floods which occurred early in 
Mars' evolution in the Ares and Tiu regions near the Pathfinder 
landing site.    

     The cover image, which is a 75-frame, color-enhanced mosaic 
taken by the Imager for Mars Pathfinder, looks to the southwest 
toward the Rock Garden, a cluster of large, angular rocks tilted 
in a downstream direction from the floods. The image shows the 
Pathfinder rover, Sojourner, snuggled against a rock nicknamed 
Moe.  The south peak of two hills, known as Twin Peaks, can be 
seen on the horizon, about 1 kilometer (6/10ths of a mile) from 
the lander. The rocky surface is comprised of materials washed 
down from the highlands and deposited in this ancient outflow 
channel by a catastrophic flood.    

     "Before the Pathfinder mission, knowledge of the kinds of 
rocks present on Mars was based mostly on the Martian meteorites 
found on Earth, which are all igneous rocks rich in magnesium and 
iron and relatively low in silica," Golombek and a team of 
Pathfinder scientists report in a paper entitled, "Overview of 
the Mars Pathfinder Mission and Assessment of Landing Site 
Predictions."  The paper summarizes the scientific results of the 
mission, which are also detailed in six other papers in this 
issue. The scientists report that chemical analyses of more than 
16 rocks and studies of different regions of soil -- along with 
spectral imaging of rock colors, textures and structures -- have 
confirmed that these rocks have compositions distinct from those 
of the Martian meteorites found on Earth. 

     "The rocks that were analyzed by the rover's alpha proton X-ray
spectrometer were basaltic or volcanic rocks, with granite-
like origins, known as andesitic rocks," Golombek reports. "The 
high silica or quartz content of some rocks suggests that they 
were formed as the crust of Mars was being recycled, or cooled 
and heated up, by the underlying mantle.  Analyses of rocks with 
lower silica content appear to be rich in sulfur, implying that 
they are covered with dust or weathered.  Rover images show that 
some rocks appear to have small air sacks or cavities, which 
would indicate that they may be volcanic.  In addition, the soils 
are chemically distinct from the rocks measured at the landing 
site."

     The remarkably successful Mars Pathfinder spacecraft, part 
of NASA's Discovery program of fast track, low-cost missions with 
highly focused science objectives, was the first spacecraft to 
explore Mars in more than 20 years.  In all, during its three 
months of operations, the mission returned about 2.6 gigabits of 
data, which included more than 16,000 images of the Martian 
landscape from the lander camera, 550 images from the rover and 
about 8.5 million temperature, pressure and wind measurements. 

     The rover traveled a total of about 100 meters (328 feet) in 
230 commanded maneuvers, performed more than 16 chemical analyses 
of rocks and soil, carried out soil mechanics and technology 
experiments, and explored about 250 square meters (820 square 
feet) of the Martian surface. The flight team lost communication 
with the lander on Sept. 27, after 83 days of daily commanding 
and data return. In all, the lander operated nearly three times 
its design lifetime of 30 days, and the small, 10.5 kilogram (23-
pound) rover operated 12 times its design lifetime of seven days.    

     Now known as the Sagan Memorial Station, the Mars Pathfinder 
mission was designed primarily to demonstrate a low-cost way of 
delivering a set of science instruments and a free-ranging rover 
to the surface of the red planet. Landers and rovers of the 
future will share the heritage of spacecraft designs and 
technologies first tested in this "pathfinding" mission.

     Golombek points out that the rocky surface and rock types 
found in Ares Vallis match the characteristics of a flood plain 
on Earth, created when a catastrophic flood washed rocks and 
surface materials from another region into the basin.  Ares 
Vallis was formed in the same way that the 40-kilometer-long (25-
mile) Ephrata Fan of the Channeled Scabland in Washington state 
was formed, says Golombek, adding that the Ephrata Fan was 
deposited when channels of water flowing down the Grand Coules 
filled the Quiney Basin. 

     Additional data from the Pathfinder landing site revealed 
that magnetic dust in the Martian atmosphere has been gradually 
blanketing most of the magnetic targets on the lander over time.  
"The dust is bright red, with magnetic properties that are 
similar to that of composite particles," Golombek states. "A 
small amount of the mineral maghemite has been deposited almost 
like a stain or cement.  These results could be interpreted to 
mean that the iron was dissolved out of crustal materials in 
water, suggesting an active hydrologic cycle on Mars.  The 
maghemite stain could be a freeze-dried precipitate."

     Another team of scientists used daily radio Doppler tracking 
and less frequent two-way radio ranging techniques during 
communications sessions with the spacecraft to pinpoint the 
location of the Pathfinder lander in inertial space and the 
direction of Mars' rotational axis. 

     In his published paper, Dr. William Folkner, an 
interdisciplinary scientist at JPL, and co-authors present 
estimates of the Martian polar moment of inertia, which show that 
Mars has a dense core surrounded by a lighter mantle.  The 
results imply that the radius of Mars' core is larger than about 
1,300 kilometers (807 miles) and less than about 2,400 kilometers 
(1,490 miles).  Mars' core and mantle are probably warmer than 
Earth's at comparable depths.  Eventually, scientists may be able 
to determine whether Mars' core is presently molten or fluid.
 
     "Variations in Mars' rotation around its own spin axis are 
thought to be dominated by mass exchange between the polar caps 
and the atmosphere," Folkner reports. "During winter, part of the 
atmosphere condenses at the poles. If the southern cap increased 
symmetrically as the northern cap decreased, then there would not 
be any change in moment of inertia or rotation rate.  However, 
because of Mars' orbital eccentricity, difference in elevation 
and difference in albedo, the polar caps are not formed 
symmetrically. 

     "The unbalanced waxing and waning of the Martian polar ice 
caps results in seasonal changes in air pressure at the 
Pathfinder and Viking landing sites, " he says.  "These changes 
in air pressure are correlated with changes in Mars' rotation 
rate, which have been observed in our radio tracking 
measurements."

     The season and time of arrival of Mars Pathfinder in the 
late northern summer resulted in some variations in the 
temperature of the upper atmosphere compared to Viking data, 
reports Dr. Tim Schofield, JPL team leader of the atmospheric 
structure and meteorology instrument, and colleagues in their 
published report.  

     High in the atmosphere, at altitudes of 80 kilometers (50 
miles) above the surface, temperatures were cold enough to make 
carbon dioxide condense and form carbon dioxide clouds.  At 
altitudes of between 60 kilometers and 120 kilometers (37 miles 
and 75 miles), the Martian atmosphere was an average of 20 
degrees colder than Viking measurements, Schofield reports.  
Seasonal variations and Pathfinder's entry at 3 a.m. local solar 
time, compared with Viking's entry at 4 p.m. local solar time, 
may account for these variations.  On the surface, however, 
daytime temperatures were typically 10 to 12 degrees warmer than 
Viking surface temperatures.  

     Mars Pathfinder measured regular pressure fluctuations twice 
a day, which suggested that a moderate amount of dust is being 
uniformly mixed in a warm lower atmosphere, as was the case with 
Viking data.  The daily average pressure reached a minimum on the 
20th day of the mission (Sol 20), indicating the winter south 
polar cap had reached its maximum size.  

     Schofield reports that surface temperatures follow a regular 
daily cycle, with a maximum of 15 degrees Fahrenheit during the 
day and a minimum of minus 105 degrees Fahrenheit at night.  The 
science team also observed rapid daytime temperature fluctuations 
of up to 30 degrees Fahrenheit in as little as 25 to 30 seconds. 
These observations suggest that cold air was warmed by the 
surface and convected upward in small eddies.   

     Pathfinder encountered winds that were light and variable 
compared to the Viking landers, Schofield reports.  The winds 
blew steadily from the south during the Martian nights, but 
during the day they rotated in a clockwise direction from south 
to west to north to east.  Whirlwinds or dust devils were 
detected repeatedly from mid-morning through the late afternoons.    

     Other scientific findings of the Mars Pathfinder mission, 
presented in this week's issue of Science, are: 

     - Chemical analyses returned by Mars Pathfinder indicate some 
rocks appear to be high in silica, suggesting differentiated 
parent materials.  These rocks are distinct from the 
meteorites found on Earth that are thought to be of Martian 
origin.  
 
     - The identification of rounded pebbles and cobbles on the 
ground, and sockets and pebbles in some rocks, suggests 
conglomerates that formed in running water, during a warmer 
past in which liquid water was stable.
 
     - The measurement of the moment of inertia of Mars by tracking 
Pathfinder radio data indicates the radius of the central 
metallic core is greater than 1300 km but less than roughly 
2000 km.
 
     - Airborne dust is magnetic with a mean size of about 1 micron. 
Interpretations suggest the magnetic mineral is maghemite, 
which may have been freeze- dried on the particles as a stain 
or cement, and that the iron may have been leached out of 
crustal materials by an active hydrologic cycle.
 
     - Remote-sensing data at a scale of generally greater than 1 
kilometer and an Earth analog correctly predicted a rocky 
plain safe for landing and roving, with a variety of rocks 
deposited by catastrophic floods that are relatively dust 
free.
 
     - Imaging revealed early morning water ice clouds in the lower 
atmosphere, which sublimate away as the atmosphere warms.
 
     - Abrupt temperature fluctuations with time and height were 
recorded in the morning, which was consistent with warming of 
the atmosphere by the surface and convected upwards in small 
eddies into the atmosphere.
 
     - Dust devils were frequently measured by temperature, wind and 
pressure sensors, and at least one likely contained dust, 
suggesting that these gusts are a mechanism for mixing dust 
into the atmosphere.
 
     - The soil chemistry of Ares Vallis appears to be similar to 
that of the Viking 1 and 2 landing sites, suggesting that the 
soil may be a globally deposited unit.
 
     - Some rocks at the landing site appear grooved and fluted, 
suggesting abrasion by saltating sand-sized particles.  Dune-
shaped deposits were also found in a trough behind the Rock 
Garden, indicating the presence of sand.
 
     - The weather was similar to the weather encountered by Viking 
1; there were rapid pressure and temperature variations, 
downslope winds at night and light winds in general. 
Temperatures at the surface were about 10 degrees Kelvin 
warmer than those measured by Viking 1.
 
     - The atmosphere has been a pale pink color due to fine dust 
mixed in the lower atmosphere, as was seen by Viking.  
Particle size and shape estimates and the amount of water 
vapor in the atmosphere are also similar to that measured by 
Viking.

     Additional information, images and rover movies from the 
Mars Pathfinder mission are available on JPL's Mars news media 
web site at http://www.jpl.nasa.gov/marsnews or on the Mars 
Pathfinder project's home page at http://marsweb.jpl.nasa.gov . 
Images from Mars Pathfinder and other planetary missions are 
available at NASA's Planetary Photojournal web site at 
http://photojournal.jpl.nasa.gov. 

     The Mars Pathfinder mission is managed by the Jet Propulsion 
Laboratory for NASA's Office of Space Science, Washington, DC. 
The mission is the second in the Discovery program of fast track, 
low-cost spacecraft with highly focused
science goals. JPL is managed by the California Institute of 
Technology, Pasadena, CA.

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