Extrasolar Planets

Varying Cloud Coverage and Reflected-Light Exoplanet Phase Curves

By Keith Cowing
March 10, 2015
Filed under
Varying Cloud Coverage and Reflected-Light Exoplanet Phase Curves

We use a planetary albedo model to investigate variations in visible wavelength phase curves of exoplanets. The presence of clouds on these exoplanets significantly alters their planetary albedo spectra.

We confirm that non-uniform cloud coverage on the dayside of tidally locked exoplanets will manifest as changes to the magnitude and shift of the phase curve. In this work, we first investigate a test case of our model using a Jupiter-like planet, at temperatures consistent to 2.0 AU insolation from a solar type star, to consider the effect of H2O clouds. We then extend our application of the model to the exoplanet Kepler-7b and consider the effect of varying cloud species, sedimentation efficiency, particle size, and cloud altitude. We show that, depending on the observational filter, the largest possible shift of the phase curve maximum will be 2-10 deg for a Jupiter-like planet, and up to 30 deg (0.08 in fractional orbital phase) for hot-Jupiter exoplanets at visible wavelengths as a function of dayside cloud distribution with a uniformly averaged thermal profile.

Finally, we tailor our model for comparison with, and confirmation of, the recent optical phase-curve observations of Kepler-7b with the Kepler space telescope. The average planetary albedo can vary between 0.1-0.6 for the 1300 cloud scenarios that were compared to the observations. We observe that smaller particle size and increasing cloud altitude have a strong effect on increasing albedo. In particular, we show that a set of models where Kepler-7b has roughly half of its dayside covered in small-particle clouds high in the atmosphere, made of bright minerals like MgSiO3 and Mg2SiO4, provide the best fits to the observed offset and magnitude of the phase-curve, whereas Fe clouds are found to have too dark to fit the observations.

Effect of Longitudinally Varying Cloud Coverage on Visible Wavelength Reflected-Light Exoplanet Phase Curves

Matthew W. Webber, Nikole K. Lewis, Mark Marley, Caroline Morley, Jonathan Fortney, Kerri Cahoy (Submitted on 3 Mar 2015)

Comments: accepted to ApJ

Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

Cite as: arXiv:1503.01028 [astro-ph.EP] (or arXiv:1503.01028v1 [astro-ph.EP] for this version)

Submission history From: Nikole Lewis [v1] Tue, 3 Mar 2015 17:52:32 GMT (2689kb) http://arxiv.org/abs/1503.01028

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