An atmospheric general circulation model for Pluto with predictions for New Horizons temperature profiles

TL;DR

This paper presents a comprehensive 3-D atmospheric model for Pluto that incorporates various heating and cooling processes, surface interactions, and predicts temperature profiles and light curves relevant for New Horizons and ground observations.

Contribution

The study develops a detailed Pluto GCM including non-LTE processes, subsurface effects, and surface-atmosphere exchange, providing novel predictions for temperature profiles and observational signatures.

Findings

Prograde jets identified at multiple altitudes.

Flow direction over poles varies with altitude.

Methane concentration affects temperature profiles and occultation light curves.

Abstract

Results are presented from a 3-D Pluto general circulation model (GCM) that includes conductive heating and cooling, non-local thermodynamic equilibrium (non-LTE) heating by methane at 2.3 and 3.3 microns, non-LTE cooling by cooling by methane at 7.6 microns, and LTE CO rotational line cooling. The GCM also includes a treatment of the subsurface temperature and surface-atmosphere mass exchange. An initially 1 m thick layer of surface nitrogen frost was assumed such that it was large enough to act as a large heat sink (compared with the solar heating term) but small enough that the water ice subsurface properties were also significant. Structure was found in all three directions of the 3-D wind field (with a maximum magnitude of order 10 m/s in the horizontal directions and 10$^-5$ microbar/s in the vertical direction). Prograde jets were found at several altitudes. The direction of flow over the poles was found to very with altitude. Broad regions of up-welling and down-welling were also found. Predictions of vertical temperature profiles are provided for the Alice and REX instruments on New Horizons, while predictions of light curves are provided for ground-based stellar occultation observations. With this model methane concentrations of 0.2% and 1.0% and 8 and 24 microbar surface pressures are distinguishable. For ground-based stellar occultations, a detectable difference exists between light curves with the different methane concentrations, but not for different initial global mean surface pressures.