Abstract:
It is becoming clear that the atmospheres of the young, self-luminous extrasolar gi-
ant 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 eld L dwarfs. The asymmetry required in the thermal radiation eld 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 disk integrated
polarization, the contribution of rotation-induced oblateness can be estimated. Using
a self-consistent, spatially homogeneous atmospheric model and a multiple scatter-
ing polarization formalism for this class of exoplanets, we show that polarization on
the order of 1% may arise due to the rotation-induced oblateness of the planets. The
observed polarization may be even higher if surface inhomogeneities exist and play
a signi catnt role. Polarized radiation from self-luminous gas giant exoplanets, if de-
tected, provides an additional tool to characterize these young planets and a new
method to constrain their surface gravity and masses.
