From Exo-Earths to Exo-Venuses – Flux and Polarization Signatures of Reflected Light

Left column: Total flow (or step function); and right column: Polarization rate of incident unpolarized starlight shown by model planets at 4 evolutionary stages as functions of α and λ. First row: Phase 1 (‘Current World’); Second line: Phase 2 (‘Thin clouds Venus’); Third row: Phase 3 (‘Thick clouds on Venus’); Fourth row: Phase 4 (‘Present Venus’). The phase functions are normalized such that at α = 0 ◦ , which is equal to the planetary geometric albedo AG. – astro-ph.EP

Earth’s exoplanets in the habitable zone are ubiquitous. However, it is not known which have Earth-like or Venus-like climates.

It is important to distinguish between different types of planets in order to determine whether a planet is habitable. We investigate the potential of polarimetry for distinguishing exo-Earths from exo-Venuses. We present the computed fluxes and polarizations of starlight reflected by exoplanets with atmospheres in the evolutionary regions from present-day Earth to present-day Venus, with clusters of clouds from pure water to a solution of 0.75 sulfuric acid, for waves between 0.3 and 2.5 microns.

The polarization of the reflected light shows larger differences with the intensity of the planetary part than the whole flow. Across the spectrum, the greatest polarization is achieved for an Earth-like atmosphere with water clouds, due to Rayleigh scattering above the clouds and the rainbow near the 40 deg phase angle.

In the near infrared, a planet with a CO2 atmosphere like Venus and thin water clouds shows prominent polarization features due to scattering by small cloud droplets. A planet orbiting Alpha Centauri A would leave temporal variations on the order of 10E-13 W/m3 in reflected flux and 10E-11 in the degree of polarization around the planet’s orbit for a planetary system that unsolved.

The planetary variation follows the order of 10E-10. Current polarimeters cannot distinguish between the possible stages of evolution of unsolved terrestrial exoplanets, since a sensitivity close to 10E-10 is required to detect a signal. a planet behind an unstable starlight.

Telescopes capable of achieving a star-planet contrast of less than 10E-9 should be able to detect the difference in the resolved polarization state as a function of its phase, thus detecting an exo-Earth in from exo-Venus depending on it. clouds’ unique polarization signatures.

Gourav Mahapatra, Fouad Abiad, Loic Rossi, Daphne M. Stam

Comments: Accepted for publication in A&A
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Materials and Methods in Astrophysics (astro-ph.IM)
Cited by: arXiv:2301.11314 [astro-ph.EP] (or arXiv:2301.11314v1 [astro-ph.EP] for this type)
Production history
From: Daphne Stam
[v1] Thursday, 26 January 2023 18:53:08 UTC (1,751 KB)

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