Application of Monte Carlo Method to Simulate Radiation Transfer through Exoplanetary Atmospheres

Development is underway of an exoplanetary atmosphere simulator Geant4-EXOPlanets (G4-EXOP) based on the Monte Carlo program package Geant4, which enables modeling transmission of radiation and particles through matter. G4-EXOP will be a toolkit to model host-star radiation transmission through atmospheric layers using radiative transition data of atoms and molecules. G4-EXOP will allow observations to be compared with simulated spectra, resolving abundances in exoplanetary atmospheres. We focus on biosignatures such as H, C, N, O, P and S and molecules containing them. We report, as a test case of G4-EXOP, Gaussian convolutions of the Kurucz simulated solar irradiance and flux residual spectra. Atomic radiative transition probabilities are calculated using SuperStructure, with phosphorus sample results being reported. Transition probabilities for molecules are obtained through ExoMol. Current work is on developing the monochromatic opacity profile module. G4-EXOP will be a toolkit for modeling host-star radiation transmission through exoplanet atmospheres to characterize biosignature abundances within observations.