Solar wind driven plasma fluxes from the Venus ionosphere

TL;DR

This study shows that Venus's ionosphere emits O+ plasma fluxes driven by solar wind kinetic energy, with measurements indicating these fluxes can exceed magnetic pressure, leading to superalfvenic flows in the wake.

Contribution

It provides new observational evidence that Venus's O+ ions are accelerated by solar wind kinetic energy rather than magnetic forces, highlighting plasma channel formation near polar regions.

Findings

O+ ion fluxes can surpass local magnetic pressure.

Detected superalfvenic flow conditions in Venus wake.

Ion beams originate near magnetic polar regions.

Abstract

Measurements conducted with the ASPERA-4 instrument and the magnetometer of the Venus Express spacecraft show that the dynamic pressure of planetary O+ ion fluxes measured in the Venus wake can be significantly larger than the local magnetic pressure and, as a result, those ions are not being driven by magnetic forces but by the kinetic energy of the solar wind. Beams of planetary O+ ions with those properties have been detected in several orbits of the Venus Express through the wake as the spacecraft traverses by the noon-midnight plane along its near polar trajectory. The momentum flux of the O+ ions leads to superalfvenic flow conditions. It is suggested that such O+ ion beams are produced in the vicinity of the magnetic polar regions of the Venus ionosphere where the solar wind erodes the local plasma leading to plasma channels that extend downstream from those regions.