Self-consistent 1D modelling of Jupiter's upper atmosphere as an exoplanet analogue

Abstract

Jupiter's upper atmosphere provides a real-world laboratory for validating first-principles models of giant gaseous exoplanets and for constraining the key physical processes that govern them. We extended the 1D first-principles thermo-chemical planetary upper atmosphere model Kompot to simulate hydrogen-rich atmospheres of giant exoplanets and benchmarked it against the archetype giant planet Jupiter. We modelled a longitudinal and latitudinal average thermal and chemical profile of Jupiter's upper atmosphere by solving the equations of energy balance, photochemical kinetics, hydrodynamics, and vertical transport in a 1D radial atmospheric grid. The thermal properties of the upper atmosphere were determined by a balance between heating from solar X-ray and ultraviolet (XUV), and infrared (IR) radiation, thermal conduction, Joule heating, and radiative cooling due to H3+ and CH4. The model results were compared with Jupiter observations from Galileo, JUNO, and other instruments. The simulation results were also used as input in the radiative transfer module of the TauREx code to simulate Jupiter's infrared transmission spectrum. Our model reproduces Jupiter's observed upper-atmospheric thermal structure and observed CH4 volume mixing ratios. The chemical abundances of other gases also exhibit strong agreement with observations and existing photochemical models. Heating and cooling results show that Joule heating is the dominant heating source throughout most of the upper atmosphere. The transmission spectrum indicates the rich presence of CH4 in the near- and mid-IR wavelength ranges. Our physically consistent model framework for Jupiter's upper atmosphere provides a validated baseline for future self-consistent simulations of the thermal and chemical structure of a diverse population of hydrogen-rich exoplanet atmospheres.