Resolving the Surfaces of Extrasolar Planets with Secondary Eclipse Light Curves

We present a method that employs the secondary eclipse light curves oftransiting extrasolar planets to probe the spatial variation of their thermalemission. This technique permits an observer to resolve the surface of theplanet without the need to spatially resolve its central star. We evaluate thefeasibility of this technique for the HD 209458 system [..]. We consider tworepresentations of the planetary thermal emission; a simple model parameterizedby a sinusoidal dependence on longitude and latitude, as well as the results ofa three-dimensional dynamical simulation of the planetary atmosphere previouslypublished by Cooper & Showman. We find that observations of the secondaryeclipse light curve are most sensitive to a longitudinal offset in thegeometric and photometric centroids of the hemisphere of the planet visiblenear opposition. To quantify this signal, we define a new parameter, the``uniform time offset,'' which measures the time lag between the observedsecondary eclipse and that predicted by a planet with a uniform surface fluxdistribution. We compare the predicted amplitude of this parameter for HD209458 with the precision with which it could be measured with IRAC. We findthat IRAC observations at 3.6um a single secondary eclipse should permitsufficient precision to confirm or reject the Cooper & Showman model of thesurface flux distribution for this planet. We quantify the signal-to-noiseratio for this offset in the remaining IRAC bands (4.5um, 5.8um, and 8.0um),and find that a modest improvement in photometric precision (as might berealized through observations of several eclipse events) should permit asimilarly robust detection.Comment: AASTeX 5.2, 24 pages, 5 figures, accepted for publication in ApJ; v2: clarifications, updated to version accepted by ApJ; v3: try to reduce spacin