Preliminary Thickness Measurements of the Seasonal Polar Carbon Dioxide Frost on Mars

Details Preliminary Thickness Measurements of the Seasonal Polar Carbon Dioxide Frost on Mars Preliminary Thickness Measurements of the Seasonal Polar Carbon Dioxide Frost on Mars

Dec 2003

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003agufm.p21a..08k&link_type=abstract

American Geophysical Union, Fall Meeting 2003, abstract #P21A-08

Physics

1863 Snow And Ice (1827), 5462 Polar Regions, 6225 Mars

Scientific paper

The exchange of carbon dioxide between the atmosphere and the polar caps on Mars creates a seasonal cycle of growth and retreat of the polar caps. CO2, the major component of the Martian atmosphere, condenses in the polar regions of the planet during the winter seasons, precipitating as CO2 frost. It then sublimates during the spring and summer seasons in response to solar radiation. The concentration of an element within the top few tens of centimeters of the surface is proportional to the flux of the gamma-rays emitted at the element's characteristic energy. Variations in the thickness of the carbon dioxide frost over time can be approximated by observing the attenuation of this signal caused by increases and decreases in CO2 coverage throughout the Martian seasons.
We have attempted here to quantize the time-dependence, spatial extent, and thickness of the polar carbon dioxide frost through the use of gamma-ray data measured by the Gamma-Ray Spectrometer (GRS) instrument suite on Mars Odyssey. Both the north and south poles are studied using the hydrogen neutron-capture gamma-ray line at 2.223 MeV.
CO2 thickness versus latitude plots are created by incorporating this gamma-ray flux data binned over 5° by 360° latitude bands. Depths are given in terms of the mass abundance of the column of CO2 (g/cm2) above the surface to avoid assumptions regarding the density of the column. As sublimation of carbon dioxide to the atmosphere occurs on one pole, the growth of the CO2 cap can be seen on the opposite pole. Retreat/growth takes place at a fairly constant rate as the seasons progress. As expected, greater frost depth is observed at increasingly poleward latitudes for both hemispheres.
The growth and retreat of the seasonal carbon dioxide frost can also be plotted at specific latitudes as a function of LS. CO2 thickness will be plotted for latitudes poleward of approximately +/-62.5° . In addition to the increase of frost depth as we move toward the poles, the CO2 cap coverage continually decreases (increases) over time for any specific latitude band from approximately LS = 0° to 180° in the north (south), at which point the frost begins again to condense (sublimate).
Polar maps of the seasonal CO2 frost can be produced from 5° by 5° gridded gamma-ray data using IDL analysis software and incorporating smoothing techniques. For all calculations, the H gamma-ray signal is basically completely attenuated above 80 g/cm2, so accurate CO2 thickness measurements are not possible.

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