Spectropolarimetric signatures of Earth-like extrasolar planets

TL;DR

This study uses numerical simulations to analyze the flux and polarization signatures of Earth-like exoplanets across different wavelengths, surface types, and atmospheric conditions, highlighting polarization's potential for planetary characterization.

Contribution

It introduces a detailed radiative transfer model that includes polarization and multiple scattering, applied to diverse planetary surface and atmospheric configurations, to improve exoplanet characterization methods.

Findings

Polarization depends strongly on phase angle, atmospheric composition, surface properties, and wavelength.

Polarization sensitivity to planetary properties differs from flux, aiding in better characterization.

Combining flux and polarization enhances the ability to analyze exoplanet features.

Abstract

We present results of numerical simulations of the flux (irradiance), F, and the degree of polarization (i.e. the ratio of polarized to total flux), P, of light that is reflected by Earth-like extrasolar planets orbiting solar-type stars, as functions of the wavelength (from 0.3 to 1.0 micron, with 0.001 micron spectral resolution) and as functions of the planetary phase angle. We use different surface coverages for our model planets, including vegetation and a Fresnel reflecting ocean, and clear and cloudy atmospheres. Our adding-doubling radiative transfer algorithm, which fully includes multiple scattering and polarization, handles horizontally homogeneous planets only; we simulate fluxes and polarization of horizontally inhomogeneous planets by weighting results for homogeneous planets. Like the flux, F, the degree of polarization, P, of the reflected starlight is shown to depend strongly on the phase angle, on the composition and structure of the planetary atmosphere, on the reflective properties of the underlying surface, and on the wavelength, in particular in wavelength regions with gaseous absorption bands. The sensitivity of P to a planet's physical properties appears to be different than that of F. Combining flux with polarization observations thus makes for a strong tool for characterizing extrasolar planets. The calculated total and polarized fluxes will be made available through the CDS.