HR: 10:55h
AN: SH42A-03    [Abstracts]
TI: Electron Observations Near ``Martian Aurora''
AU: * Winningham, J D
EM: dwinningham@swri.edu
AF: Southwest Research Institute, 6220 Culebra Road, San Antonio, 78238 United States
AU: Frahm, R A
EM: rfrahm@swri.edu
AF: Southwest Research Institute, 6220 Culebra Road, San Antonio, 78238 United States
AU: Sharber, J R
EM: jsharber@swri.edu
AF: Southwest Research Institute, 6220 Culebra Road, San Antonio, 78238 United States
AU: Liemohn, M W
EM: liemohn@umich.edu
AF: Space Physics Research Laboratory, University of Michigan, 2455 Hayward Street, Ann Arbor, MI 48105 United States
AU: Ma, Y
EM: yingjuan@umich.edu
AF: Space Physics Research Laboratory, University of Michigan, 2455 Hayward Street, Ann Arbor, MI 48105 United States
AU: Coates, A J
EM: ajc@mssl.ucl.ac.uk
AF: Mullard Space Science Laboratory, University College London, Holmbury St. Mary, Dorking, Surry, RH5 6NT United Kingdom
AU: Linder, D R
EM: drl@mssl.ucl.ac.uk
AF: Mullard Space Science Laboratory, University College London, Holmbury St. Mary, Dorking, Surry, RH5 6NT United Kingdom
AU: Soobiah, Y
EM: yijs@mssl.ucl.ac.uk
AF: Mullard Space Science Laboratory, University College London, Holmbury St. Mary, Dorking, Surry, RH5 6NT United Kingdom
AU: Team, A
EM: stas@irf.se
AF: Swedish Institute of Space Physics, Box 812, Kiruna, S-981 Sweden
AB: Earlier in 2005, Bertaux et al. in a letter to Nature titled ``Discovery of an Aurora on Mars'' reported an observation of a UV aurora on Mars as measured by the Spectroscopy for the Investigation of the Characteristics of the Atmosphere of Mars (SPICAM) experiment on the Mars Express (MEX) spacecraft. We have examined the electron observations for the same time period as the reported aurora using the Analyzer of Space Plasmas and Energetic Atoms (ASPERA-3) Electron Spectrometer (ELS), also on MEX. SPICAM and ELS do not observe the same volume of space, but do survey the same large region of near-vertical remanent Martian crustal magnetic field. During the auroral observation period, MEX crossed several regions of near-vertical fields based on the Cain et al. 2003 model and ELS observed brief bursts of low-energy electrons. No pitch angle data was available at that time as the field of view of ELS is approximately parallel to the Martian surface. Examination of the burst spectra showed evidence of Martian atmospheric photoelectrons, including carbon dioxide peaks from exobase emissions. At the time of observation, both MEX and the Mars atmosphere beneath were not sunlit. Thus, the photoelectrons must have come from a sunlit region of Mars. Ray tracing with the Cain et al. model shows that the filed lines within the bursts are closed loops connecting to Mars, with one field line foot in the Martian day-lit region. Results will be presented from the University of Michigan MHD model (which includes external magnetic fields) that will show, with a more sophisticated model, that the observed particles are on closed magnetic field loops. Thus, one can more accurately call the UV emissions ``airglow'' rather than ``aurora''.
DE: 2760 Plasma convection (2463)
DE: 5408 Aurorae and airglow
DE: 5440 Magnetic fields and magnetism
DE: 5443 Magnetospheres (2756)
DE: 6225 Mars
SC: SPA-Solar and Heliospheric Physics [SH]
MN: Fall Meeting 2005