Polarized Signatures of a Habitable World: Comparing Models of an Exoplanet Earth with Visible and Near-infrared Earthshine Spectra

Abstract

In the JWST, Extremely Large Telescopes, and LUVOIR era, we expect to characterize a number of potentially habitable Earth-like exoplanets. However, the characterization of these worlds depends crucially on the accuracy of theoretical models. Validating these models against observations of planets with known properties will be key for the future characterization of terrestrial exoplanets. Due to its sensitivity to the micro- and macro-physical properties of an atmosphere, polarimetry will be an important tool that, in tandem with traditional flux-only observations, will enhance the capabilities of characterizing Earth-like planets. In this paper we benchmark two different polarization-enabled radiative-transfer codes against each other and against unique linear spectropolarimetric observations of the earthshine that cover wavelengths from $\sim$0.4 to $\sim$2.3 $\mu$m. We find that while the results from the two codes generally agree with each other, there is a phase dependency between the compared models. Additionally, with our current assumptions, the models from both codes underestimate the level of polarization of the earthshine. We also report an interesting discrepancy between our models and the observed 1.27 $\mu$m $O_2$ feature in the earthshine, and provide an analysis of potential methods for matching this feature. Our results suggest that only having access to the 1.27 $\mu$m $O_2$ feature coupled with a lack of observations of the $O_2$ A and B bands could result in a mischaracterization of an Earth-like atmosphere. Providing these assessments is vital to aid the community in the search for life beyond the solar system.

24 pages, 18 figures

References in corpus (18)

• Direct Imaging of Multiple Planets Orbiting the Star HR 8799
• The Detectability and Characterization of the TRAPPIST-1 Exoplanet Atmospheres with JWST
• The Occurrence of Rocky Habitable Zone Planets Around Solar-Like Stars from Kepler Data
• Spectropolarimetric signatures of Earth-like extrasolar planets
• Detectability of atmospheric features of Earth-like planets in the habitable zone around M dwarfs
• The Effects of Refraction on Transit Transmission Spectroscopy: Application to Earth-like Exoplanets
• Prospects for Detecting Oxygen, Water, and Chlorophyll on an Exo-Earth
• Empirically Determining Substellar Cloud Compositions in the era of JWST
• Sensitive Probing of Exoplanetary Oxygen via Mid Infrared Collisional Absorption
• Optimizing Ground-based Observations of O2 in Earth Analogs
• The intrinsic and interstellar broadband linear polarization of nearby FGK dwarfs
• Blue, white, and red ocean planets - Simulations of orbital variations in flux and polarization colors
• The Detectability and Constraints of Biosignature Gases in the Near & Mid-Infrared from Transit Transmission Spectroscopy
• Detectability of biosignatures on LHS 1140 b
• Colors of an Earth-like exoplanet -- Temporal flux and polarization signals of the Earth
• Polarimetric signature of the oceans as detected by near-infrared Earthshine observations
• The cloudbow of planet Earth observed in polarisation
• High-Resolution Spectral Discriminants of Ocean Loss for M Dwarf Terrestrial Exoplanets

Cited by in corpus (1)

• Light Scattering Measurements of KCl Particles as an Exoplanet Cloud Analog