Photometric Variability in Earthshine Observations

TL;DR

This study analyzes earthshine light curves to understand Earth's photometric variability, highlighting the potential of specular reflection as an indicator of liquid water on exoplanets.

Contribution

It demonstrates how earthshine observations can reveal surface changes and suggests specular reflection as a key method for detecting liquid water on exoplanets.

Findings

Brightness variability up to 23% per hour at 600 nm

Spectral reddening associated with surface changes

Specular reflection can indicate liquid water presence

Abstract

The identification of an extrasolar planet as Earth-like will depend on the detection of atmospheric signatures or surface non-uniformities. In this paper we present spatially unresolved flux light curves of Earth for the purpose of studying a prototype extrasolar terrestrial planet. Our monitoring of the photometric variability of earthshine revealed changes of up to 23 % per hour in the brightness of Earth's scattered light at around 600 nm, due to the removal of specular reflection from the view of the Moon. This variability is accompanied by reddening of the spectrum, and results from a change in surface properties across the continental boundary between the Indian Ocean and Africa's east coast. Our results based on earthshine monitoring indicate that specular reflection should provide a useful tool in determining the presence of liquid water on extrasolar planets via photometric observations.