PUBLIC INFORMATION OFFICE
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http://www.jpl.nasa.gov
Contact: Diane Ainsworth
Dec. 1, 1997
EMBARGOED FOR RELEASE AT 4 P.M. EST DECEMBER 4
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://mars.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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