HR: 09:45h
AN: P41B-08    [Abstracts]
TI: Coherent Electromagnetic Waves Observed Upstream of the Venus Bow Shock Recorded by the MESSENGER Magnetometer Experiment
AU: * Korth, H
EM: haje.korth@jhuapl.edu
AF: The Johns Hopkins University Applied Physics Laboratory, 11100 Johns Hopkins Rd., Laurel, MD 20723, United States
AU: Anderson, B J
EM: brian.anderson@jhuapl.edu
AF: The Johns Hopkins University Applied Physics Laboratory, 11100 Johns Hopkins Rd., Laurel, MD 20723, United States
AU: Acuna, M H
EM: mario.acuna@nasa.gov
AF: Goddard Space Flight Center, 8800 Greenbelt Road, Greenbelt, MD 20771, United States
AU: Slavin, J A
EM: james.a.slavin@nasa.gov
AF: Goddard Space Flight Center, 8800 Greenbelt Road, Greenbelt, MD 20771, United States
AU: Boardsen, S A
EM: scott.a.boardsen.1@gsfc.nasa.gov
AF: Goddard Space Flight Center, 8800 Greenbelt Road, Greenbelt, MD 20771, United States
AB: The MESSENGER gravity assist maneuver at Venus on 5 June 2007 provided an opportunity to observe the interaction of Venus with the solar wind along a unique trajectory through the Venus environment. Closest approach (CA) occurred near 23:08 UTC on 5 June, and the Magnetometer experiment identified the inbound shock crossing at 22:57:55 UTC on 5 June and the outbound crossing at 00:43:47 UTC on 6 June. The Magnetometer experiment operated at its maximum sampling rate for a 12-hour span centered on CA, providing continuous coverage of magnetic signatures of electromagnetic waves up to 10 Hz. Prior to the inbound shock crossing, three intense foreshock magnetic field intensifications, analogous to hot flow anomalies documented at Earth's bow shock, were observed from 22:56:40 to 22:57:35 UTC on 5 June. The first upstream waves were observed as early as 22:25 UTC, more than 30 minutes upstream of the shock crossing at distance of 3 Venus radii upstream of the shock. These waves occurred in two narrow frequency bands, one near 0.05 Hz corresponding to a gyrofrequency of ions with M/Q in the range 10 to 20, and another near 1 Hz corresponding to a gyrofrequency of ions with M/Q near 1. Both waves increased in intensity with decreasing distance from the shock, but the lower-frequency waves ceased around 22:47 UTC whereas the higher-frequency waves persisted up to the inbound shock crossing. The higher-frequency waves were observed again following the outbound shock crossing. We attribute the 1-Hz waves to an ion cyclotron instability excited by solar wind ions reflected upstream by the shock. The lower-frequency waves are consistent with heavy ions originating from the Venus ionosphere and accelerated upstream by the shock.
DE: 2152 Pickup ions
DE: 2154 Planetary bow shocks
DE: 2159 Plasma waves and turbulence
DE: 2164 Solar wind plasma
DE: 6295 Venus
SC: Planetary Sciences [P]
MN: 2007 Fall Meeting