Cool Stars 14 - Submitted Abstract # 279
This version created on 05 October 2006

Earth as an Exoplanet:  Determining the Rotational Period and Presence
of Clouds from Photometric Simulations


Enric Palle, Big Bear Solar Observatory (NJIT)
Eric B. Ford, Harvard-Smithsonian Center for Astrophysics
Sara Seager, Carnegie Institution of Washington
Manuel Vazquez, Instituto de Astrofisica de Canarias
Pilar P. Montanes-Rodriguez, Big Bear Solar Observatory (NJIT)

Future observations will aim to determine the surface and atmospheric
properties of extrasolar planets similar to the Earth.  Here, we have
modeled changes in the apparent brightness of the Earth (as a function
of its phase angle, and in the direction of the observer's) due to the
rotation and orbital motion of the Earth, as well as to the temporal
variability of clouds and ice (on daily and seasonal timescales).  We
apply reflectance models that have been previously validated with
observations of the Earthshine that illuminates the dark side of the
Moon.  We use real cloud data from satellite observations to
characterize the hourly, diurnal, and seasonal variability that we
might observed in earth-like extrasolar planets.  We find that
measuring the rotation period of the Earth is non-trivial, even for
high signal-to-noise observations, largely due to the temporal
variability of cloud cover on timescales comparable to the rotation
period.  If the rotation period can be measured, then deviations from
a periodiic signal can be used to infer the presence of tracers
(relatively short-living structures) in its atmosphere (i.e., clouds).
This could provide a useful technique for recognizing exoplanets that
have weather (i.e., cloud cover changing on a diurnal timescale).
Such variability is likely to be related to the atmospheric
temperature and pressure being near a phase transition.  Thus, such
observations could support the possibility of liquid water on an
extrasolar planet

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