Results from the first lunar-wake flyby of ARTEMIS on wake potential, electron beams, and electrostatic waves

The ARTEMIS (Acceleration, Reconnection, Turbulence, and Electrodynamics of the Moon’s Interaction with the Sun) mission is a new two-probe lunar mission derived from the THEMIS (Time History of Events and Macroscale Interactions During Substorms) mission. On Feb 13, 2010, one of the two probes, ARTEMIS P1 (formerly THEMIS-B), made the first lunar-wake flyby of the mission. Halekas et al. [2010] reported observations of electron beams and derived the wake potential along this flyby. They suggested that the electron beams result from the net potential across the wake. In this presentation, we will show that the net potential is a result of the asymmetric electron distribution function of the solar wind and the quasi-neutrality condition. The electric field waveforms of both low-frequency and high-frequency electrostatic waves associated with the electron beams from the on-board Electric Field Instrument (EFI) will be reported. The low-frequency waves around ion cyclotron frequency showed oblique propagation, and seemed to be associated with the deceleration of the electron beams. The high-frequency electrostatic waves had a broadband spectrogram that is consistent with beam mode. We derived the wave number of the high-frequency waves using high time-resolution EFI data, and performed 1D Vlasov simulations to study the generation mechanism of the high-frequency waves. The results of the simulations are consistent with the observations of the electron beams and the derived potential structure by Halekas, et al. [2010]. Reference: Halekas, et al., 2010. First results from ARTEMIS, a new two-spacecraft lunar mission: Counter-streaming plasma populations in the lunar plasma wake. Space Sci. Rev., submitted.