Martian Atmospheric Density Near 250km Altitude From MRO Radio Tracking Data

Details Martian Atmospheric Density Near 250km Altitude From MRO Radio Tracking Data Martian Atmospheric Density Near 250km Altitude From MRO Radio Tracking Data

Dec 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007agufm.p32a..04m&link_type=abstract

American Geophysical Union, Fall Meeting 2007, abstract #P32A-04

Physics

0350 Pressure, Density, And Temperature, 5405 Atmospheres (0343, 1060), 5445 Meteorology (3346), 6225 Mars, 6952 Radar Atmospheric Physics (1220)

Scientific paper

We present the atmospheric density results obtained from more than one year of Mars Reconnaissance Orbiter spacecraft (MRO) radio tracking data. The stronger signature of atmospheric drag in the MRO Doppler data, compared to the Mars Global Surveyor and Mars Odyssey missions, enables density estimation at higher temporal frequency, up to once every 2 orbits (4h). We processed the high quality, 1-second Doppler tracking data in short arcs using the GEODYN program, starting after the October 2006 solar conjunction. We first used long-arc durations (desaturation maneuvers are separated by 2 to 3 days), but the arc convergence started to deteriorate in April-May 2007. This increase in the Doppler residuals is linked to the seasonal density enhancement. The a priori atmospheric models do not completely capture the density structure, and modeling errors accumulate. Thus, we shortened the arcs (0.7day), with no data gap greater than 5 hours and no desaturation maneuver. The resulting Doppler residual RMS is low (0.7-0.8mm/s) and stable from arc to arc. To assess the robustness of the measurements and evaluate the temporal variability of the density, we processed the tracking data using different sets of a priori models and adjustable physical parameters. Densities calculated from two independent a priori atmospheric models (Stewart 1987 and the recent MCD4.2) show reasonable agreement, given the large prediction discrepancy. We also used MCD4.2 with a high dust opacity setting starting June 2007 to account for the dust storm observed by various remote sensing instruments. We use the obtained density results to evaluate those models. Taking into account the self-shadowing effect on the spacecraft cross-section in the force modeling has an influence on the drag and solar radiation estimation, but surprisingly not on the arc convergence. Of course, the density estimation frequency strongly influences the results. The scatter and formal uncertainty of the measurements increase when we decrease the estimation periods. We calculate the density variability at different timescales from various time series (2, 3, 4 and 6 orbits). The current seasonal trend of increasing atmospheric density is clearly visible in our results, from 10- 13kg.m-3 in November 2006 to 8.10-12kg.m-3 in June 2007 (at 250km altitude above the South Pole). However, contrary to previous MGS and Odyssey results, we do not detect the solar rotation periodicity in the density time series, because of low solar activity and more efficient CO2 cooling processes at lower altitude.

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