Models of Polarized Light from Oceans and Atmospheres of Earth-like Extrasolar Planets

More from this morning's astro-ph. It is a neat idea, particularly
for any one who has had the pleasure of flying over a large body of
water and looking down to see the Sun glint off the surface of the
water.

astro-ph/0610518
Title: Models of Polarized Light from Oceans and Atmospheres of
Earth-like Extrasolar Planets
Authors: P. R. McCullough

Specularly reflected light, or glint, from an ocean surface may
provide a useful observational tool for studying extrasolar
terrestrial planets. Detection of sea-surface glints would
differentiate ocean-bearing terrestrial planets, i.e. those similar to
Earth, from other terrestrial extrasolar planets. The brightness and
degree of polarization of both sea-surface glints and atmospheric
Rayleigh scattering are strong functions of the phase angle of the
extrasolar planet. We modify analytic expressions for the
bi-directional reflectances previously validated by satellite imagery
of the Earth to account for the fractional linear polarization of
sea-surface reflections and of Rayleigh scattering in the
atmosphere. We compare our models with Earth's total visual light and
degree of linear polarization as observed in the ashen light of the
Moon, or Earthshine. We predict the spatially-integrated reflected
light and its degree of polarization as functions of the diurnal cycle
and orbital phase of Earth and Earth-like planets of various imagined
types. The difference in polarized reflectances of Earth-like planets
may increase greatly the detectability of such planets in the glare of
their host star. Finally, sea-surface glints potentially may provide a
practical means to map the boundaries between oceans and continents on
extrasolar planets.

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