HR: 14:40h
AN: P52B-05    [PDF]
TI: Measuring Mars' Atmospheric Neutral Density from 160 to 320km altitude with the MGS Electron Reflectometer
AU: * Lillis, R J
EM: rlillis@ssl.berkeley.edu
AF: Space Sciences Laboratory, University of California Berkeley, 7 Gauss Way, Berkeley, CA 94720 United States
AU: Mitchell, D L
EM: mitchell@ssl.berkeley.edu
AF: Space Sciences Laboratory, University of California Berkeley, 7 Gauss Way, Berkeley, CA 94720 United States
AU: Lin, R P
EM: rlin@ssl.berkeley.edu
AF: Space Sciences Laboratory, University of California Berkeley, 7 Gauss Way, Berkeley, CA 94720 United States
AU: Acuna, M H
EM: mario.h.acuna@gsfc.nasa.gov
AF: NASA Goddard Space Flight Center, Greenbelt Rd., Greenbelt, MD 20771 United States
AB: The Magnetometer/Electron Reflectometer (MAG/ER) experiment aboard Mars Global Surveyor (MGS) samples the local electron population's distribution in energy and pitch angle (angle between electron velocity and local magneticfield direction) at the mapping orbit altitude of ~400km. We develop a single-particle model of the electrons' interaction with the neutral atmosphere and motion along open field-lines connecting the solar wind to remnant crustal magnetization. Electron reflection from magnetic gradients and absorption due to inelastic collisons with atmospheric neutrals results in characteristic pitch angle (PA) distributions for open field lines. By assuming the validity of spherical harmonic expansions (Cain, Arkani-hamed) in the strongest field regions of Mars (such as Terra Sirenum), we trace the electron paths and fit these PA distributions to our model to constrain the scale height and base density of the neutral atmosphere in the interaction region, which is between 160 and 320km altitude. We analyse ~2 martian years of MGS mapping Orbit Data and present the first measurements of Mars' exospheric neutral density. We track density variations over season, latitude and solar cycle and compare with predictions from Mars Thermosphere Global Circulation Model (MTGCM) simulations and with MGS acceleromater data. Our results will help to constrain the upper boundaries of GCMs and assist orbital decay calculations for low-orbiting spacecraft, such as the 2005 Mars Reconnaissance Orbiter.
DE: 0343 Planetary atmospheres (5405, 5407, 5409, 5704, 5705, 5707)
DE: 5405 Atmospheres--composition and chemistry
DE: 5409 Atmospheres--structure and dynamics
DE: 5440 Magnetic fields and magnetism
DE: 5443 Magnetospheres (2756)
SC: Planetary Sciences [P]
MN: 2003 Fall Meeting