On the escape of CH4 from Pluto's atmosphere

TL;DR

This study models the escape rates of methane and nitrogen from Pluto's atmosphere, showing that methane's escape is limited and can be constrained by observations, providing insights into atmospheric escape processes.

Contribution

It adapts a multi-species escape model for Pluto, linking methane escape rates to observational data to test atmospheric escape theories.

Findings

Methane escape rate is 5-10% of nitrogen's.

Methane maintains a <1% mixing ratio below the exobase.

Observations can constrain methane escape rates.

Abstract

We adapted a multi-species escape model, developed for close-in extrasolar planets, to calculate the escape rates of CH4 and N2 from Pluto. In the absence of escape, CH4 should overtake N2 as the dominant species below the exobase. The CH4 profile depends strongly on the escape rate, however, and the typical escape rates predicted for Pluto lead to a nearly constant mixing ratio of less than 1 % below the exobase. In this case the CH4 escape rate is only 5-10 % of the N2 escape rate. Observations of the CH4 profile by the New Horizons/ALICE spectrograph can constrain the CH4 escape rate and provide a unique test for escape models.