Journal Article

Probing the physical properties of directly imaged gas giant exoplanets through polarization

Mark S. Marley and Sujan Sengupta

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 417, issue 4, pages 2874-2881
Published in print November 2011 | ISSN: 0035-8711
Published online November 2011 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2011.19448.x
Probing the physical properties of directly imaged gas giant exoplanets through polarization

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It has been becoming clear that the atmospheres of the young, self-luminous extrasolar giant planets imaged to date are dusty. Planets with dusty atmospheres may exhibit detectable amounts of linear polarization in the near-infrared, as has been observed from some field L dwarfs. The asymmetry required in the thermal radiation field to produce polarization may arise either from the rotation-induced oblateness or from surface inhomogeneities, such as partial cloudiness. While it is not possible at present to predict the extent to which atmospheric dynamics on a given planet may produce surface inhomogeneities substantial enough to produce net non-zero disc-integrated polarization, the contribution of rotation-induced oblateness can be estimated. Using a self-consistent, spatially homogeneous atmospheric model and a multiple scattering polarization formalism for this class of exoplanets, we show that polarization of the order of 1 per cent may arise due to the rotation-induced oblateness of the planets. The degree of polarization for cloudy planets should peak at the same wavelengths at which the planets are brightest in the near-infrared. The observed polarization may be even higher if surface inhomogeneities exist and play a significant role. Polarized radiation from self-luminous gas giant exoplanets, if detected, provides an additional tool to characterize these young planets and a new method to constrain their surface gravity and masses.

Keywords: polarization; scattering; planets and satellites: atmospheres; stars: atmospheres

Journal Article.  5463 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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