Abstract:
An alternative generation mechanism for the electrostatic waves observed in the lunar wake
during the first flyby of the Acceleration, Reconnection, Turbulence and Electrodynamics of the Moon’s
Interaction with the Sun (ARTEMIS) mission in terms of slow and fast ion-acoustic and electron-acoustic
solitons is proposed. The lunar wake plasma is modeled by fluid multicomponent magnetized plasma
comprising hot protons, hot heavier ions, 𝛼 particles (He++), electron beam, and suprathermal electrons
following kappa distribution. The electric fields associated with the slow and fast ion-acoustic and
electron-acoustic solitons are in the range of ∼(0.0003–17) mV m−1. This is in excellent agreement with
observed electrostatic wave electric field of 5 to 15 mV m−1. The fast Fourier transform of soliton electric
fields generates broadband spectra having peak frequencies (corresponding to peak in the power spectra)
in the range of ∼(3–1800) Hz. This corresponds to wave frequencies being in the range of ∼(0.001–0.56)fpe,
where fpe is the electron plasma frequency. This matches well with the observed frequency range of
(0.01–0.4) fpe. Further, the widths and velocities of these solitons are in the range ∼(100–8000) m and
∼(30–1300) km s−1, respectively. Both, soliton widths and velocities, match well with the estimated
wavelengths (a few hundred meters to a couple of thousand meters) and estimated phase velocities
(of the order of 1000 km s−1) of the electrostatic waves in the lunar wake.
