Extreme induced magnetospheres

The structure and dynamics of induced magnetospheres around non-magnetized planets such as Mars and Venus are entirely driven by upstream conditions. These are defined by the solar wind density and velocity, as well as the magnitude and direction of the interplanetary magnetic field (IMF). Certain extreme values of these upstream parameters or specific combinations of them can result in distinct interaction regimes that are morphologically different from the nominal case.

The best-studied examples to date are the degenerate induced magnetosphere (DIM) and the disappearing magnetosphere. The former corresponds to cases where the IMF cone angle is very small (typically <5°-10°), while the latter is associated with extremely low solar wind densities (as low as ~0.05 cm⁻³).

We review extreme cases of morphologically distinct induced magnetospheres, with a focus on the DIM. We also propose a physics-based classification of these extreme cases and outline the main open scientific questions relevant to each category.

Finally, we discuss the importance of studying such interaction regimes, as insights gained may be applicable to understanding:

• Stellar wind–exoplanet interactions
• The space environments of exotic objects (e.g., free-floating planets)
• Past or future solar system conditions
• Moon–magnetosphere interactions around outer planets