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Title: The O{sub 2} A-Band in the Fluxes and Polarization of Starlight Reflected by Earth-Like Exoplanets

Abstract

Earth-like, potentially habitable exoplanets are prime targets in the search for extraterrestrial life. Information about their atmospheres and surfaces can be derived by analyzing the light of the parent star reflected by the planet. We investigate the influence of the surface albedo A {sub s}, the optical thickness b {sub cloud}, the altitude of water clouds, and the mixing ratio of biosignature O{sub 2} on the strength of the O{sub 2} A-band (around 760 nm) in the flux and polarization spectra of starlight reflected by Earth-like exoplanets. Our computations for horizontally homogeneous planets show that small mixing ratios ( η < 0.4) will yield moderately deep bands in flux and moderate-to-small band strengths in polarization, and that clouds will usually decrease the band depth in flux and the band strength in polarization. However, cloud influence will be strongly dependent on properties such as optical thickness, top altitude, particle phase, coverage fraction, and horizontal distribution. Depending on the surface albedo and cloud properties, different O{sub 2} mixing ratios η can give similar absorption-band depths in flux and band strengths in polarization, especially if the clouds have moderate-to-high optical thicknesses. Measuring both the flux and the polarization is essential to reduce themore » degeneracies, although it will not solve them, especially not for horizontally inhomogeneous planets. Observations at a wide range of phase angles and with a high temporal resolution could help to derive cloud properties and, once those are known, the mixing ratio of O{sub 2} or any other absorbing gas.« less

Authors:
 [1]; ;  [2]
  1. Laboratoire d’Optique Atmosphèrique (LOA), UMR 8518, Université Lille 1, Villeneuve d’Ascq (France)
  2. Faculty of Aerospace Engineering, Delft University of Technology, Kluyverweg 1, 2629 HS Delft (Netherlands)
Publication Date:
OSTI Identifier:
22663516
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 842; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ABSORPTION; ALTITUDE; ATMOSPHERES; CLOUDS; COMPUTERIZED SIMULATION; DISTRIBUTION; MIXING RATIO; MOLECULES; OXYGEN; PLANETS; POLARIZATION; RESOLUTION; SPECTRA; STARS; THICKNESS; VISIBLE RADIATION; WATER

Citation Formats

Fauchez, Thomas, Rossi, Loic, and Stam, Daphne M. The O{sub 2} A-Band in the Fluxes and Polarization of Starlight Reflected by Earth-Like Exoplanets. United States: N. p., 2017. Web. doi:10.3847/1538-4357/AA6E53.
Fauchez, Thomas, Rossi, Loic, & Stam, Daphne M. The O{sub 2} A-Band in the Fluxes and Polarization of Starlight Reflected by Earth-Like Exoplanets. United States. doi:10.3847/1538-4357/AA6E53.
Fauchez, Thomas, Rossi, Loic, and Stam, Daphne M. Sat . "The O{sub 2} A-Band in the Fluxes and Polarization of Starlight Reflected by Earth-Like Exoplanets". United States. doi:10.3847/1538-4357/AA6E53.
@article{osti_22663516,
title = {The O{sub 2} A-Band in the Fluxes and Polarization of Starlight Reflected by Earth-Like Exoplanets},
author = {Fauchez, Thomas and Rossi, Loic and Stam, Daphne M.},
abstractNote = {Earth-like, potentially habitable exoplanets are prime targets in the search for extraterrestrial life. Information about their atmospheres and surfaces can be derived by analyzing the light of the parent star reflected by the planet. We investigate the influence of the surface albedo A {sub s}, the optical thickness b {sub cloud}, the altitude of water clouds, and the mixing ratio of biosignature O{sub 2} on the strength of the O{sub 2} A-band (around 760 nm) in the flux and polarization spectra of starlight reflected by Earth-like exoplanets. Our computations for horizontally homogeneous planets show that small mixing ratios ( η < 0.4) will yield moderately deep bands in flux and moderate-to-small band strengths in polarization, and that clouds will usually decrease the band depth in flux and the band strength in polarization. However, cloud influence will be strongly dependent on properties such as optical thickness, top altitude, particle phase, coverage fraction, and horizontal distribution. Depending on the surface albedo and cloud properties, different O{sub 2} mixing ratios η can give similar absorption-band depths in flux and band strengths in polarization, especially if the clouds have moderate-to-high optical thicknesses. Measuring both the flux and the polarization is essential to reduce the degeneracies, although it will not solve them, especially not for horizontally inhomogeneous planets. Observations at a wide range of phase angles and with a high temporal resolution could help to derive cloud properties and, once those are known, the mixing ratio of O{sub 2} or any other absorbing gas.},
doi = {10.3847/1538-4357/AA6E53},
journal = {Astrophysical Journal},
number = 1,
volume = 842,
place = {United States},
year = {Sat Jun 10 00:00:00 EDT 2017},
month = {Sat Jun 10 00:00:00 EDT 2017}
}