Terran World Spectral Simulator

Abstract

The Terran world Spectral Simulator (TSS) is a flexible software package for modeling direct detection of reflected stellar radiation from Earth-similar terrestrial exoplanets. Exoplanets similar to Earth require more sophisticated simulation tools than planets with optically thick atmospheres, because both the atmospheric composition and spatial distribution of clouds and surface materials will impact the integrated reflected radiation. Thus, accurate simulations need to employ a three-dimensional approach where the exoplanet surface and cloud field are explicitly modeled. Our modeling framework is designed using a modular approach which splits the explicit radiative transfer calculations from the geometric calculations to produce a disk-integrated reflectance. The modular layout allows different radiative transfer models to be used, and their outputs can be efficiently re-used in larger simulations of orbital phase or rotational light curves. The model is designed to compute unpolarized disk-integrated reflectance spectra. These simulated spectra can help inform preparatory science activities for future direct-imaging missions, such as the WFIRST CGI, HabEx, and LUVOIR. This work highlights several case studies using the TSS: simulation of rotational light curves for a modern Earth twin, simulation of the EPOXI Earth observations, and simulation of a past Earth from a paleoclimate simulation. These case studies illustrate that the TSS simulations agree well with the EPOXI Earth observations, and illustrates how the TSS can be used to support exoplanet research.