Colors of a Second Earth: Estimating the fractional areas of ocean, land, and vegetation of Earth-like exoplanets

TL;DR

This paper introduces a simple method to estimate the fractional surface areas of ocean, land, snow, and vegetation on Earth-like exoplanets using photometric light curves, aiding the search for life beyond our planet.

Contribution

The paper presents a novel reconstruction approach that accurately estimates surface composition and detects vegetation signatures from photometric data of exoplanets.

Findings

Reproduces fractional surface areas with good accuracy under ideal noise conditions.

Detects vegetation signature (red edge) from photometric variations.

Estimates presence of oceans and atmospheres simultaneously.

Abstract

Characterizing the surfaces of rocky exoplanets via the scattered light will be an essential challenge to investigate the existence of life on habitable exoplanets. We present a simple reconstruction method for fractional areas of different surface types from photometric variations, or colors, of a second Earth. We create mock light curves for Earth without clouds using empirical data. Then these light curves are fitted to the isotropic scattering model consisting of 4 surface types: ocean, soil, snow and vegetation. In an idealized situation where the photometric errors are only photon shot noise, we are able to reproduce the fractional areas of those components fairly well. We may be even able to detect a signature of vegetation from the distinct feature of photosynthesis on the Earth, known as the red edge. In our reconstruction method, Rayleigh scattering due to the atmosphere has an important effect, and for terrestrial exoplanets with atmosphere similar to our Earth, it is possible to estimate the presence of oceans and an atmosphere simultaneously.