Global Mapping of Earth-like Exoplanets from Scattered Light Curves

TL;DR

This paper presents a method to reconstruct global land distribution and measure obliquity of Earth-like exoplanets using scattered light curves, assuming ideal conditions, with potential application in future space missions.

Contribution

It develops a novel surface mapping technique from light curves that includes latitude and longitude resolution and demonstrates its feasibility with Earth-like planet models.

Findings

Global land distribution can be reconstructed under ideal conditions.

Obliquity can be estimated from light curve dependence.

Method is feasible for nearby Earth-like planets with future missions.

Abstract

Scattered lights from terrestrial exoplanets provide valuable information about the planetary surface. Applying the surface reconstruction method proposed by Fujii et al. (2010) to both diurnal and annual variations of the scattered light, we develop a reconstruction method of land distribution with both longitudinal and latitudinal resolutions. We find that one can recover a global map of an idealized Earth-like planet on the following assumptions: 1) cloudless, 2) a face-on circular orbit, 3) known surface types and their reflectance spectra 4) no atmospheric absorption, 5) known rotation rate 6) static map, and 7) no moon. Using the dependence of light curves on the planetary obliquity, we also show that the obliquity can be measured by adopting the chi-square minimization or the extended information criterion. We demonstrate a feasibility of our methodology by applying it to a multi-band photometry of a cloudless model Earth with future space missions such as the occulting ozone observatory (O3). We conclude that future space missions can estimate both the surface distribution and the obliquity at least for cloudless Earth-like planets within 5 pc.