Joint Inversion of Time-variable Elevation and Gravity to Reveal Seasonal and Inter- annual Changes of the Volume Density of Martian Snow

Details Joint Inversion of Time-variable Elevation and Gravity to Reveal Seasonal and Inter- annual Changes of the Volume Density of Martian Snow Joint Inversion of Time-variable Elevation and Gravity to Reveal Seasonal and Inter- annual Changes of the Volume Density of Martian Snow

Dec 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufm.g53c..08m&link_type=abstract

American Geophysical Union, Fall Meeting 2008, abstract #G53C-08

Physics

0736 Snow (1827, 1863), 1217 Time Variable Gravity (7223, 7230), 1221 Lunar And Planetary Geodesy And Gravity (5417, 5450, 5714, 5744, 6019, 6250), 5422 Ices, 6225 Mars

Scientific paper

The Martian atmosphere seasonally exchanges CO2 with the surface by repeating condensation and sublimation, causing seasonal growth and decay of the polar CO2 snow caps. These processes leave two kinds of geodetic signatures, i.e. seasonal changes of the Martian gravity field and of surface elevation of the snow-covered regions. These were simultaneously observed by Doppler tracking of MGS as time-variable J3 component [Konopliv et al., 2006], and by laser altimetry from the satellite [Smith et al., 2001], respectively. Here we study gradual increase of the volume density of the Martian snow due to compaction, by combining the two data sets 1999-2001 covering three Martian winters. We tried three models, (model 1) constant density throughout the year, (model 2) gradually increasing density with the same peak value, and (model 3) gradually increasing density with different peak values for the three winters, and found that the agreement between the two data sets gets better as we increase the number of parameters. We found that light fresh snow of about 0.1 g/cm3 slowly becomes denser reaching about 1.0 g/cm3 or more immediately before it thaws. From analogy to terrestrial H2O snow, we suggest densification mechanisms such as gravity-driven compaction and/or sintering of CO2 crystals. The densities reached their maxima when solar longitude was 60"|85 degrees (northern hemisphere, equivalent to May-Jun. of the Earth) and 240"|265 degrees (southern hemisphere, Nov.-Dec.). The maximum snow density varies slightly from year to year, and between hemispheres. In the second southern winter, the density became as high as ~1.6 g/cm3 possibly reflecting enhanced mixing ratio of silicate particles by a large-scale dust storm that occurred around the South Pole early in 2000 (solar longitude 270-285 degrees). We also evaluated sources of systematic errors, such as atmospheric pressure variations (factor A), influence of elastic deformation of the solid Mars by snow loads onto the two observed quantities, gravity (factor B) and elevation (factor C). Among them, factor B might introduce systematic underestimation of snow densities, but inferred load Love numbers of Mars suggest that this error would not exceed ten percent.

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