Other
Scientific paper
Dec 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufm.p31d..07z&link_type=abstract
American Geophysical Union, Fall Meeting 2008, abstract #P31D-07
Other
1217 Time Variable Gravity (7223, 7230), 1218 Mass Balance (0762, 1223, 1631, 1836, 1843, 3010, 3322, 4532), 6225 Mars
Scientific paper
Since February 1999, one and at times multiple spacecraft have been operating in Mars orbit, continuously tracked by the NASA Deep Space Network. This nearly decade-long time series of tracking observations has afforded the opportunity to monitor the Martian gravity field and its miniscule changes due to the seasonal cycling of the primary atmospheric constituent, CO2, between the planet's atmosphere and surface. Beginning with Mars Global Surveyor (MGS), followed by Mars Odyssey (Odyssey), and finally Mars Reconnaissance Orbiter (MRO) we have recovered changes in the masses of the seasonal icecaps and the atmosphere through analyses of small perturbations of the orbits of the spacecraft. Using models of the two seasonal icecaps derived from temporal spectral and altimetric observations and a general circulation model (GCM) of the atmosphere as a priori constraints, we have obtained estimates of the masses of the CO2 on each of the icecaps and the mean global atmospheric pressure at 5-day intervals for over 4 Mars years (approx. 8 Earth years). MGS and Odyssey provide the strongest solutions because the altitude (approx. 400 km) of both spacecraft dictates that their orbits are less affected by atmospheric drag than spacecraft in lower-altitude orbits. MRO, with a periapse at 255 km, is more sensitive to Mars' gravity but also more affected by atmospheric drag and its variability, making the identification of the very small seasonal changes in the gravity field more difficult to extract. Clear but small inter-annual departures from the predictions of GCMs are evident and some are consistent across years, suggesting that other processes could be involved in the seasonal cycling of volatiles. Gravity is the only measurement able to detect these changes.
Mazarico Erwan
Smith Douglas E.
Torrence Mark H.
Zuber Maria T.
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