Degenerate induced magnetospheres

Induced magnetospheres of non-magnetized atmospheric bodies like Mars and Venus are formed by magnetic fields of ionospheric currents induced by the convective electric field E = - V x B/c of the solar wind. When the interplanetary magnetic field is mostly radial (the cone angle θ is close to 0°, quasi-parallel conditions) and the convective field E ≈ 0, an induced magnetosphere becomes degenerate. The degenerate induced magnetospheres can be considered as a specific type of the interaction with ambient plasma. This type of interaction were observed at Venus and Mars, for example, 12 observed cases for Venus and 17 observed cases for Mars for θ < 10° as recorded by Venus Express (2006-2014) and Mars express (2014-2019). However, the quasi-parallel conditions are nominal for the majority of discovered exoplanets (hot Jupiters) orbiting the parent stars on distances 0.01 – 0.1 au when θ < 4° (assuming the solar conditions). The conditions at some moons of icy giants, Neptune (Triton) and Uranus, are also quasi-parallel due to large angle between magnetic dipole and the rotation axis though the plasma flow is subsonic.

In this report we introduce degenerate induced magnetospheres as a new type of interaction and review the current works on the subject. We also show examples of observations at Mars and Venus and numerical simulations, and describe the main properties and basic physics of such configurations.