HR: 09:45h
AN: P21A-08 [PDF]
TI: Preliminary Thickness Measurements of the Seasonal Polar Carbon Dioxide Frost on Mars
AU: * Kelly, N J
EM: nkelly@gamma1.lpl.arizona.edu
AF: Lunar and Planetary Laboratory, University of Arizona
1629 E. University Blvd., Tucson, AZ 85721-0092 United States
AU: Boynton, W V
EM: wboynton@gamma1.lpl.arizona.edu
AF: Lunar and Planetary Laboratory, University of Arizona
1629 E. University Blvd., Tucson, AZ 85721-0092 United States
AU: Boynton, W V
EM: wboynton@gamma1.lpl.arizona.edu
AF: Department of Planetary Science, University of Arizona
1629 E. University Blvd., Tucson, AZ 85721-0092 United States
AU: Kerry, K
EM: krisk@gamma1.lpl.arizona.edu
AF: Lunar and Planetary Laboratory, University of Arizona
1629 E. University Blvd., Tucson, AZ 85721-0092 United States
AU: Hamara, D
EM: daveh@lpl.arizona.edu
AF: Lunar and Planetary Laboratory, University of Arizona
1629 E. University Blvd., Tucson, AZ 85721-0092 United States
AU: Janes, D
EM: buck@gamma1.lpl.arizona.edu
AF: Lunar and Planetary Laboratory, University of Arizona
1629 E. University Blvd., Tucson, AZ 85721-0092 United States
AU: Feldman, W C
AF: Los Alamos National Laboratory, P.O. Box 1663, Los Alamos, NM 87545 United States
AU: Prettyman, T H
AF: Los Alamos National Laboratory, P.O. Box 1663, Los Alamos, NM 87545 United States
AB:
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. CO$_{2}$, the major component of the Martian atmosphere, condenses in the polar regions of the
planet during the winter seasons, precipitating as CO$_{2}$ 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 CO$_{2}$ 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. \\ \\
CO$_{2}$ thickness versus latitude plots are created by incorporating this gamma-ray flux data binned over $5\deg$ by
$360\deg$ latitude bands. Depths are given in terms of the mass abundance of the column of CO$_{2}$ (g/cm$^{2}$) 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 CO$_{2}$ 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
L$_{S}$. CO$_{2}$ thickness will be plotted for latitudes poleward of approximately $\pm$$62.5\deg$. In addition to the
increase of frost depth as we move toward the poles, the CO$_{2}$ cap coverage continually decreases (increases) over time
for any specific latitude band from approximately L$_{S}$ = $0\deg$ to $180\deg$ in the north (south), at which point the
frost begins again to condense (sublimate). \\ \\
Polar maps of the seasonal CO$_{2}$ frost can be produced from $5\deg$ by $5\deg$ 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/cm$^{2}$, so accurate CO$_{2}$ thickness measurements are not possible.
DE: 1863 Snow and ice (1827)
DE: 5462 Polar regions
DE: 6225 Mars
SC: Planetary Sciences [P]
MN: 2003 Fall Meeting