HR: 09:45h
AN: SH41C-07    [Abstracts]
TI: Solar Wind Interaction with Venus and Mars: Comparison of Proton Pickup Rates
AU: * Wei, H
EM: hwei@igpp.ucla.edu
AF: University of California Los Angeles, Institute of Geophysics and Planetary Physics, 405 Hilgard Ave., Los Angeles, CA 90095-1567 United States
AU: Russell, C T
EM: ctrussell@igpp.ucla.edu
AF: University of California Los Angeles, Institute of Geophysics and Planetary Physics, 405 Hilgard Ave., Los Angeles, CA 90095-1567 United States
AU: Blanco-Cano, X
EM: xbc@geofisica.unam.mx
AF: Ciudad Universitaria, Inst. of Geophysics., UNAM Coyoaacan, Codigo, 04510, Mexico, D.F 04510
AB: Both Venus and Mars are unmagnetized planets whose ionospheres stand off the solar wind forming an ionopause, magnetosheath and standing bow shock. These planets can be compared using Pioneer Venus and Mars Global Surveyor data, and shortly with data from Venus Express. The principal difference in the solar wind from Venus to Mars is a decrease in the solar wind number density and the magnetic field strength. As a result, the dynamic pressure decreases, and the Mach number of the solar wind flow increases from Venus to Mars. The difference in the size of the planets may also be important. The radius of Mars and the escape velocity are close to half those of Venus. Pioneer Venus and Mars Global Surveyor data show that while the Mars solar wind interaction superficially resembles that of Venus, the occurrence of proton cyclotron waves in the solar wind near the two planets is very different. About 30 percent of the time proton cyclotron waves are found extending from the magnetosheath of Mars to over 12 RM with amplitudes that vary only slowly with distance. In contrast proton cyclotron waves at Venus appear to be confined to the magnetosheath. Since the electromagnetic energy flux of proton cyclotron waves is proportional to the rate of loss of the hydrogen exosphere from the planet, this simple observation indicates that Mars is losing hydrogen at a much more rapid rate than Venus at the present time.
DE: 5421 Interactions with particles and fields
DE: 6225 Mars
DE: 6295 Venus
SC: SPA-Solar and Heliospheric Physics [SH]
MN: Fall Meeting 2005