Observing the Earth as an exoplanet with LOUPE, the Lunar Observatory for Unresolved Polarimetry of Earth

TL;DR

LOUPE is a small spectropolarimeter designed to observe Earth from the Moon, providing crucial data for characterizing rocky exoplanets and testing atmospheric retrieval algorithms.

Contribution

This paper introduces LOUPE, a novel lunar-based instrument for observing Earth as an unresolved exoplanet, aiding exoplanet habitability assessments.

Findings

Provides Earth signals for exoplanet characterization algorithms

Enables observation of Earth’s disk-integrated polarization signals

Supports testing of atmospheric and surface retrieval methods

Abstract

The detections of small, rocky exoplanets have surged in recent years and will likely continue to do so. To know whether a rocky exoplanet is habitable, we have to characterise its atmosphere and surface. A promising characterisation method for rocky exoplanets is direct detection using spectropolarimetry. This method will be based on single pixel signals, because spatially resolving exoplanets is impossible with current and near-future instruments. Well-tested retrieval algorithms are essential to interpret these single pixel signals in terms of atmospheric composition, cloud and surface coverage. Observations of Earth itself provide the obvious benchmark data for testing such algorithms. The observations should provide signals that are integrated over the Earth's disk, that capture day and night variations, and all phase angles. The Moon is a unique platform from where the Earth can be observed as an exoplanet, undisturbed, all of the time. Here, we present LOUPE, the Lunar Observatory for Unresolved Polarimetry of Earth, a small and robust spectropolarimeter to observe our Earth as an exoplanet.