Propagation of nonlinear ion-acoustic fluctuations in the mantle of Venus

Abstract

Motivated by the observations of ion-acoustic fluctuations with the Parker Solar Probe (PSP) and earlier by the Pioneer Venus Orbiter (PVO) in the Venusian magnetosheath, we investigate the nature of ion-acoustic solitary and double-layer (DL) structures in the mantle. We employed a hydrodynamic description along with reductive perturbation theory to derive the nonlinear Zakharov–Kuznetsov equation that elucidates the dynamics of three-dimensional ion-acoustic wave packets. Using the spacecraft measurements of the plasma configuration at Venus, we carried out a parametric analysis of these structures, including the influence of the magnetic field strength and the relative densities and temperatures, considering two cases: quasi-parallel and oblique propagation. Moreover, we determined the structural characteristics of these waves, where oblique (quasi-parallel) solitary waves have a potential of $0.4$ V ($0.4$ V) and a maximum electric field amplitude $E_m mV/m ($8$ mV/m) across spatial and temporal widths of $ km ($ 140-200$ m) and $0.4$ s ($1.6$ ms). These waves produce low-frequency electrostatic activity in the frequency range of $1.6-10$ Hz ($630-3160$ Hz). Quasi-parallel DLs have potential drops of ($6.5-13$) V and $E_m mV/m with a width and duration of $(100-120)$ m and $ 1$ ms, and a frequency range of $ Hz. These outcomes can explain the detected electrostatic fluctuations above the ionosphere via PVO in the frequency channels of $730$ Hz and $5.4$ kHz. Furthermore, the DL features estimated in this work are in line with the recent PSP measurements of the DLs propagating in the magnetosheath of Venus.