Mapping Clouds and Terrain of Earth-like Planets from Photometric Variability: Demonstration with Planets in Face-on Orbits

TL;DR

This paper presents a novel inversion technique to create two-dimensional albedo maps of Earth-like exoplanets from photometric light curves, enabling the detection of surface features like continents and vegetation.

Contribution

The study introduces a new method for mapping exoplanet surfaces using photometric variability, including cloud reduction and surface feature identification, demonstrated on simulated Earth-twin data.

Findings

Cloud distribution dominates the primary albedo map feature.

Difference in reflectivity bands can recover continental layouts.

Vegetation features are detectable via red-edge reflectivity differences.

Abstract

We develop an inversion technique of annual scattered light curves to sketch a two-dimensional albedo map of exoplanets in face-on orbits. As a test-bed for future observations of extrasolar terrestrial planets, we apply this mapping technique to simulated light curves of a mock Earth-twin at a distance of 10 pc in a face-on circular orbit. A primary feature in recovered albedo maps traces the annual mean distribution of clouds. To extract information of other surface types, we attempt to reduce the cloud signal by taking difference of two bands. We find that the inversion of reflectivity difference between 0.8-0.9 and 0.4-0.5 micron bands roughly recover the continental distribution, except for high latitude regions persistently covered with clouds and snow. The inversion of the reflectivity difference across the red edge (0.8-0.9 and 0.6-0.7 micron) emphasizes the vegetation features near the equator. The planetary obliquity and equinox can be estimated simultaneously with the mapping under the presence of clouds. We conclude that the photometric variability of the scattered light will be a powerful means for exploring the habitat of a second Earth.