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1998 American Geophysical Union Abstracts

Morning turbulence observed near Mars' surface with Mars Pathfinder

J. D. Mihalov (
R. M. Haberle (
J. R. Murphy (
MS245-3, Planetary Systems Branch, NASA-Ames Research Center
Moffett Field, California 94035-1000 U. S. A.

A. Seiff (
G. R. Wilson (
San Jose State Univ. Foundation/NASA-Ames Research Center
Moffett Field, California 94035-1000 U. S. A.

G. R. Wilson (
Arizona State University/NASA-Ames Research Center
Moffett Field, California 94035-1000 U. S. A.

For several hours as Mars' surface warmed each morning, prominent atmospheric thermal fluctuations were measured by Mars Pathfinder with thin-wire thermocouples at three heights on the 1.1 m long meteorology mast. A major component of these fluctuations appears to be not completely random in nature, but rather may be due to the movement past the mast of distinct atmospheric parcels that belong to several different families. The time scales associated with these parcels range from ~200 s down to a 4 s limit of experimental resolution. Some data were acquired with higher time resolution. Distinct atmospheric parcels are identified from temperature ratios available from the temperatures measured at different heights, as well as from computed temperature gradients. Different families of atmospheric parcels that have been identified are: 1) those with a "normal" daytime gradient, which increased with time from 0 (neutrally stable) to - ~9 deg K/m, as the mornings progressed; 2) those during the morning but with positive temperature gradients, up to several deg K/m, characteristic of nighttime conditions; 3) those with abnormally steep negative gradients, up to twice "normal" values. The incidence of these various atmospheric surface layer microstates was found to change between Sols 25 and 69; during this time the maximum sun angles decreased and the days became shorter.

SC: P DE: 3379 DE: 6225 DE: 3307 MN: 1998 Spring Meeting

Chemistry of Rocks and Soil at Ares Vallis in Comparison to Martian Meteorites

*G Dreibus (
J. Brueckner
R Rieder
H. Wänke
Max-Planck-Institut f. Chemie, PO Box 3060
Mainz D-55020 Germany

T. Economou
Enrico Fermi Institute, University of Chicago
Chicago Ilinois, IL 60637 USA

The APXS (Alpha-Proton-X-ray-Spectrometer) analyses of the Mars Pathfinder Mission demonstrate significant chemical differences between rocks and soil at the Ares Vallis landing site. The soils with their high S- and Cl-contents have similar compositions to those measured by Viking at two different sites separated by thousands of kilometers. The mineralogy of Martian soils at least at mean latitudes can be explained as weathering products of mafic igneous rocks with a high content of sulfate and chloride salts. The Pathfinder rocks with their high Si, Al, and K content but low Mg abundance can be interpreted as highly differentiated crustal material, whereas the 12 martian meteorites ejected from the martian surface to Earth in probably 5 events have varying but generally more mafic compositions. Most of the rocks on Mars are partially covered by dust which is indicated by their high S content and ranges from several percent to about half of their surface area. Using a linear regression calculation based on the correlation of S with each element the composition of a ‘soil-free’ rock was calculated. When comparing the composition of rocks and soils of Ares Vallis it appears that the martian soil cannot be made directly from the nearby rocks through weathering processes. Components much richer in Mg, Cr and Fe and lower in Si and K as observed in the martian meteorites have to be added. More detailed analyses of the APXS data for minor elements, especially for Cr and Mn, provide further insight into the relationship between martian rocks, soils and meteorites.

SC: P DE: 1060 DE: 5400 DE: 5470 MN: 1998 Spring Meeting

Comparisons of Ground-based Millimeter and TES Infrared Temperature Profile Sounding of the Mars Atmosphere (Sep97-Mar98)

*R. T. Clancy (
Space Science Institute, 1540 30th St., Suite 22
Boulder, CO 80303-1012 USA

B. J. Sandor
NCAR, P.O. Box 3000
Boulder, CO 80307 USA

P. R. Christensen
Geology Department, Arizona State University
Tempe, AZ 85287 USA

J. C. Pearl
B. J. Conrath
M. D. Smith
GSFC, MC 693 0
Greenbelt, MD 20771 USA

Ground-based monitoring of the millimter and submillimeter rotational lines of Mars atmospheric CO allows retrieval of disk-average atmospheric temperature profiles over the 0-80 km altitude range. The long-term accumulation of such measurements have supported conclusions that the Mars atmosphere is typically colder and less dusty than the Viking model of Mars climate; that interactions between dust-ice cloud aerosols play a major role in large orbital variations of the compositional and thermal structure of the Mars atmosphere (Clancy et al., Icarus, 122, 1996); and that condensation of the CO2 atmosphere is common in the cold mesosphere of Mars (Clancy and Sandor, GRL, 24,1998). These conclusions have been called into question by imaging and meteorological analyses of Pathfinder measurements (Smith et al. and Schofield et al., Science, 278, 1997), implying a large (minus 15-20K) bias in the millimeter temperature profiles. As part of MGS aerobraking operations, both ground-based (millimeter and submillimeter) and TES IR temperature profiling have been obtained with a high frequency over the Sep96 to Mar97 period (Ls=180-290). Comparisons between the two methods of temperature retrievals show excellent (better than 5K) agreement, during very clear/cold atmospheric conditions (compared to Viking) and during a perihelion dust storm event in November of 1997.

SC: P DE: 5405 DE: 5409 DE: 5464 MN: 1998 Spring Meeting

Mars 2001 Landing Site Selection

*M. S. Gilmore
R S. Saunders (
Jet Propulsion Laboratory, Mail Stop 183-335
4800 Oak Grove Drive
Pasadena, CA 91106 USA

G. Briggs
C. McKay
NASA Ames Research Center

M. Carr
US Geological Survey

D. Crown
U. Pittsburgh

M. Duke
Lunar and Planetary Institute

G. McGill
U. Massachusetts USA

D. Paige

S. Squyres
Cornell U.

J. Zimbleman
National Air and Space Museum

The Mars Surveyor Program (MSP) ‘01 mission consists of an orbiter, lander and rover that will complete the global characterization studies of Mars, perform experiments in preparation for human exploration, and select rock and soil samples to be cached and returned to Earth in a subsequent mission (2004 launch). In keeping with the themes set forth by NASA for Mars exploration: 1) the search for life, 2) understanding climate history, and 3) mapping of resources, the preferred site for the 2001 rover is to be on the ancient Noachian highlands where conditions are most likely to preserve possible evidence for prebiotic or biotic components. Given engineering constraints for the mission of 15&#176;S - 5&#176;N latitude, and <2.5 km above the 6.1 mbar datum, approximately 50 sites have been thus far proposed by the planetary community [Mars Surveyor 2001 Landing Site Workshop, NASA Ames Research Center, Jan. 26, 27, 1998]. The majority of the sites are within Xanthe Terra, S. Arabia Terra, SE Elysium Planitia, S. Isidis Planitia, and within Valles Marineris and represent a variety of geological environments. In order to maximize the chances of finding life, the optimal site should have the following characteristics: accessible Noachian-age materials, evidence of surface or subsurface water, a mechanism of concentration of possible organic components (such as a lake bed), evidence of an energy mechanism such as volcano or large impact crater basin which could provide heat, and a mechanism of rapid burial for better preservation. Detailed mapping using image data from Viking and, where possible, the Mars Global Surveyor camera now in orbit are being utilized to determine the geology of each site. Following the example of Pathfinder, each site is being assessed to ascertain rock abundance, surface slopes and other fundamental surface properties in order to minimize hazard and maximize spacecraft performance. We are also weighing the benefits of several sampling strategies; a site with several interesting features within reach of the rover is likely the most desirable.

SC: P DE: 6225 DE: 5470 DE: 6297 MN: 1998 Spring Meeting

Detection of Thermospheric Density Bulges on Opposite Sides of Mars and Major Global Thermospheric Response to a Regional Dust Storm

*G M Keating
R H. Tolson
D. T. Baird
G. J. Cancro
S. N. Noll
J. S. Parker
T. J. Schellenberg (
George Washington University/ NASA Langley, MS 269
Hampton, VA 23681

S. W. Bougher
University of Arizona
Tucson, AZ 85721

R. W. Zurek
Jet Propulsion Laboratory
Pasadena, CA 91109

J. L. Hollingsworth
J. R Murphy
NASA Ames Research Center
Moffett Field, CA 94035

R T. Clancy
Space Science Institute
Boulder, CO 80309

J. C. Pearl
B. J. Conrath
M. D. Smith
NASA Goddard Space Flight Center
Greenbelt, MD 20771

R C. Blanchard
NASA Langley Research Center
Hampton, VA 23681

The Mars Global Surveyor (MGS) spacecraft carries an accelerometer which points essentially along the velocity vector in the vicinity of periapsis. The MGS Accelerometer Experiment measures atmospheric drag effects over about 30 degrees of latitude. The accelerometer is 38 times more sensitive than the Viking accelerometers, has a dynamic range of 700, and is extremely stable. The MGS Accelerometer Experiment has already obtained in situ measurements of over 200 thermospheric vertical structures ranging in altitude from 110 km to 170km, compared to only three in the past from Viking 1, Viking 2, and Mars Pathfinder. Persistent thermospheric density bulges have been discovered in the Northern Hemisphere on opposite sides of Mars near 90 W and 90 E longitude, in the vicinity of the Tharsis and Arabia highlands. This Wave 2 pattern, occurring in both the upper and lower thermosphere (and not like the Earth's thermosphere), may be caused by topographically-forced planetary waves propagating up from the lower atmosphere. On November 25, 1997, a regional dust storm occurred in the martian Southern Hemisphere, in the Noachis Terra region centered near 30 S, 30 E, heating and expanding the lower atmosphere. Within 3 days, the effect of the storm resulted in a 130\% increase of thermospheric densities near 40 N latitude, and eventually raised the thermosphere by as much as 8 km. The effect of the storm in the Northern Hemisphere upper and lower thermosphere took about 1 month to subside as the dust settled. Previously it had been thought that only global dust storms would have such global effects in the thermosphere. Other results, in addition to dust storm and wave 2 effects, include thermospheric storms without increased dust activity, colder than expected temperatures near 130 km, generally disturbed conditions, and strong gravity wave activity.

SC: P DE: 0343 DE: 5409 DE: 6225 MN: 1998 Spring Meeting

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