DPS 2001 meeting, November 2001
Session 19. Mars Atmosphere Posters
Displayed, 9:00am Tuesday - 3:00pm Saturday, Highlighted, Wednesday, November 28, 2001, 10:30am-12:30pm, French Market Exhibit Hall

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[19.29] Unpredictable day-to-day variability in the martian upper atmosphere

P. Withers, S. W. Bougher (University of Arizona), G. M. Keating (George Washington University/NASA Langley)

Mars Global Surveyor Accelerometer measurements of density in the martian upper atmosphere during aerobraking are now available via the PDS [Keating et al, 2001].

When the martian day was an integer multiple of the spacecraft orbital period, the accelerometer measured densities at the same latitude, local solar time, season, and longitude each martian day. This period of resonance lasted for several days as the spacecraft orbital period decreased through the critical value due to drag. This lets us examine the intrinsic, daily variability of the martian upper atmosphere.

Characterising and understanding such variability is crucial for the success of future aerobraking and aerocapture.

Intrinsic variability in density shows no obvious correlation with longitude or the significant zonal structure in longitude. Measurements made on the inbound and outbound legs of a periapsis pass, which differ only in latitude, show no obvious correlation with latitude. Since there were multiple resonances during aerobraking and since periapsis latitude precessed during aerobraking, we can examine the intrinsic variability at a given latitude, local solar time, (approximately) season, and longitude at times separated by a few weeks. These show significant changes in the intrinsic variability over such timescales.

Intrinsic variability decreases as altitude increases. When the inbound and outbound legs of a periapsis pass are on opposite sides of the terminator and periapsis is near the pole, we can examine intrinsic variability at the same latitude and season at two different local solar times. No obvious differences between night and day are found.

Preliminary results from Mars Odyssey's accelerometer may be available at the time of the meeting.

G.M. Keating, R.H. Tolson, J.L. Hanna, R.F. Beebe, J.R. Murphy and L.F. Huber, MGS-M-ACCEL-5-ALTITUDE-V1.0, NASA Planetary Data System, 2001.

The author(s) of this abstract have provided an email address for comments about the abstract: withers@lpl.arizona.edu

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