Energy Dissipation in the Upper Atmospheres of Trappist-1 Planets

TL;DR

This paper introduces a method to estimate the maximum energy transfer from stellar wind to the upper atmospheres of Trappist-1 planets, highlighting potential for significant atmospheric heating.

Contribution

It develops a formalism treating the system as two electromagnetic regions to quantify upper-limit energy transmission from stellar wind to planetary atmospheres.

Findings

High stellar wind energy flux can cause substantial atmospheric heating.

Ohmic energy dissipation can reach 0.5-1 W/m^2, about 1% of stellar irradiance.

Potential for large atmospheric heating in terrestrial planets and hot Jupiters.

Abstract

We present a method to quantify the upper-limit of the energy transmitted from the intense stellar wind to the upper atmospheres of three of the Trappist-1 planets (e, f, and g). We use a formalism that treats the system as two electromagnetic regions, where the efficiency of the energy transmission between one region (the stellar wind at the planetary orbits) to the other (the planetary ionospheres) depends on the relation between the conductances and impedances of the two regions. Since the energy flux of the stellar wind is very high at these planetary orbits, we find that for the case of high transmission efficiency (when the conductances and impedances are close in magnitude), the energy dissipation in the upper planetary atmospheres is also very large. On average, the Ohmic energy can reach $0.5-1~W/m^2$, about 1\% of the stellar irradiance and 5-15 times the EUV irradiance. Here, using constant values for the ionospheric conductance, we demonstrate that the stellar wind energy could potentially drive large atmospheric heating in terrestrial planets, as well as in hot jupiters. More detailed calculations are needed to assess the ionospheric conductance and to determine more accurately the amount of heating the stellar wind can drive in close-orbit planets.