Evidence of haze control of Pluto’s atmospheric heat balance from JWST/MIRI thermal light curves

Abstract

Pluto and its largest moon Charon display a variety of surfaces, whose thermal and energetic properties are largely unknown. Previous thermal measurements of the Pluto–Charon system yield multiple solutions because most of them did not resolve Pluto from Charon. In addition, recent modelling studies suggest that the atmospheric haze of Pluto could substantially contribute to its mid-infrared emission, thus adding further degeneracy. Here we measure separate Pluto and Charon thermal light curves over 15–25.5 μm with JWST and retrieve the thermophysical and emissivity properties of the different terrains on each. We also detect and measure the thermal emission of Pluto’s haze. The observed fluxes indicate that Pluto’s haze is composed of Titan-like organic particles as well as hydrocarbon and nitrile ices and demonstrate that the haze largely controls Pluto’s atmospheric balance. As a result, Pluto’s temperatures, climate and general circulation should therefore be substantially affected by the haze across seasons.