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David E. Smith,1*Maria T. Zuber,12Gregory A. Neumann12
Using topography collected over one martian year from the Mars
Orbiter Laser Altimeter on the Mars Global Surveyor (MGS) spacecraft,we have measured temporal changes in the elevation of the martiansurface that correlate with the seasonal cycle of carbon dioxideexchange between the surface and atmosphere. The greatest elevationchange (1.5 to 2 meters) occurs at high latitudes ( above 80°),whereas the bulk of the mass exchange occurs at lower latitudes(below
75° N and below 73° S). An unexpected period of sublimationwas
observed during northern hemisphere autumn, coincident withdust storms
in the southern hemisphere. Analysis of MGS Dopplertracking residuals
revealed temporal variations in the flatteningof Mars that correlate
with elevation changes. The combined changesin gravity and elevation
constrain the average density of seasonallydeposited carbon dioxide to
be 910 ± 230 kilograms per cubic meter,which is considerably
denser than terrestrial snow.
1 Laboratory for Terrestrial Physics,
NASA/Goddard Space Flight Center, Greenbelt, MD 20771, USA.
2 Massachusetts Institute of Technology, Cambridge,
MA 02139-4307, USA.
*
To whom correspondence should be addressed. E-mail:
dsmith{at}tharsis.gsfc.nasa.gov
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