Extrasolar giant magnetospheric response to steady-state stellar wind pressure at 10, 5, 1, and 0.2 AU

TL;DR

This study uses 3D multifluid simulations to explore how a giant planet's magnetosphere responds to steady stellar wind pressure at various orbital distances, revealing effects on magnetospheric dynamics, plasma processes, and potential observables.

Contribution

It provides new insights into the magnetospheric behavior of exoplanets at different orbital distances, including the impact of stellar wind pressure on plasma dynamics and auroral currents.

Findings

Magnetospheric size decreases with closer orbit due to increased stellar wind pressure.

Mass loss processes vary with orbital distance, with interchange instability only at larger orbits.

Enhanced ion density and plasma torus features could be observable in warm exoplanets.

Abstract

A three-dimensional, multifluid simulation of a giant planet's magnetospheric interaction with steady-state stellar wind from a Sun-like star was performed for four different orbital semi-major axes - 10, 5, 1 and 0.2 AU. We simulate the effect of the increasing, steady-state stellar wind pressure related to the planetary orbital semi-major axis on the global magnetospheric dynamics for a Saturn-like planet, including an Enceladus-like plasma torus. Mass loss processes are shown to vary with orbital distance, with the centrifugal interchange instability displayed only in the 10 AU and 5 AU cases which reach a state of mass loss equilibrium more slowly than the 1 AU or 0.2 AU cases. The compression of the magnetosphere in the 1 AU and 0.2 AU cases contributes to the quenching of the interchange process by increasing the ratio of total plasma thermal energy to corotational energy. The strength of field-aligned currents (FAC), associated with auroral radio emissions, are shown to increase in magnitude and latitudinal coverage with a corresponding shift equatorward from increased dynamic ram pressure experienced in the hotter orbits. Similar to observed hot Jovian planets, the warm exo-Saturn simulated in the current work shows enhanced ion density in the magnetosheath and magnetopause regions, as well as the plasma torus which could contribute to altered transit signals, suggesting that for planets in warmer ($>$0.1 AU) orbits, planetary magnetic field strengths and possibly exomoons - via the plasma torus - could be observable with future missions.