Mapping Earth Analogs from Photometric Variability: Spin-Orbit Tomography for Planets in Inclined Orbits

TL;DR

This paper extends the spin-orbit tomography method to inclined planetary orbits, demonstrating its ability to reconstruct surface features like clouds and continents from simulated light curves, aiding exoplanet habitability studies.

Contribution

It generalizes the SOT technique for inclined orbits and validates its effectiveness with simulations of Earth-like planets in various configurations.

Findings

Successfully retrieved surface features from simulated inclined orbit light curves.

Demonstrated model-independent surface mapping applicable to diverse planetary inhomogeneities.

Extended the SOT method to planets with different obliquities and orbital inclinations.

Abstract

Aiming at obtaining detailed information of surface environment of Earth analogs, Kawahara & Fujii (2011) proposed an inversion technique of annual scattered light curves named the spin-orbit tomography (SOT), which enables one to sketch a two-dimensional albedo map from annual variation of the disk-integrated scattered light, and demonstrated the method with a planet in a face-on orbit. We extend it to be applicable to general geometric configurations, including low-obliquity planets like the Earth in inclined orbits. We simulate light curves of the Earth in an inclined orbit in three photometric bands (0.4-0.5um, 0.6-0.7um, and 0.8-0.9um) and show that the distribution of clouds, snow, and continents is retrieved with the aid of the SOT. We also demonstrate the SOT by applying it to an upright Earth, a tidally locked Earth, and Earth analogs with ancient continental configurations. The inversion is model independent in the sense that we do not assume specific albedo models when mapping the surface, and hence applicable in principle to any kind of inhomogeneity. This method can potentially serve as a unique tool to investigate the exohabitats/exoclimes of Earth analogs.