Other
Scientific paper
Dec 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufm.p14a..08p&link_type=abstract
American Geophysical Union, Fall Meeting 2010, abstract #P14A-08
Other
[5405] Planetary Sciences: Solid Surface Planets / Atmospheres, [5464] Planetary Sciences: Solid Surface Planets / Remote Sensing
Scientific paper
Exoplanet observations offer the potential to study planetary atmospheres at stages of evolution not accessible in our own solar system. The detection of any atmosphere at all around an M-dwarf Super-Earth class planet would provide a powerful constraint on theories of atmospheric escape. We propose a method for detection and characterization of atmospheres through thermal infrared photometry. The method takes advantage of the changing infrared emission seen by a distant observer, caused by the variation in which part of the planet is viewed as it proceeds in its orbit. We focus on the novel issues presented by planets with a distinct surface. We present a catalog of thermal emission signatures pertinent to planets in close-orbits about M-dwarfs. Such planets are expected to be in tide-locked, quasi-synchronous spin states, or 3:2 spin-orbit resonances, and have a very hot spot under the subsolar point, and a very cold nightside, particularly when the atmosphere is thin or absent. When there is an atmosphere, the low Coriolis force makes heat transport very efficient, leading to an atmosphere that is horizontally isothermal. This behavior is familiar from the WTG approximation widely applied to the Earth's tropics, and we have verified by GCM simulations that it applies globally for planets in slow spin-states. When the atmosphere is optically thick in some parts of the thermal infrared, the dichotomy beween atmospheric and surface temperature contrasts leaves a characteristic imprint on the thermal emission time series. The figure illustrates the method for a tide-locked planet in a circular orbit, with stellar luminosity and semi-major axis similar to Gliese 581c. The orbit is viewed edge-on but transit effects are not shown. We show synthetic observations at two wavenumbers, for both an airless case and a case with an isothermal atmosphere. In the optically thick band, the the atmosphere shows up in the moderation of the photometry curve. We will also show signatures for planets in eccentric orbits and other spin states, and from simulations of partially ice-covered waterworlds. Typical ratios of planetary to stellar fluxes are on the order of ten ppm. For a system ten light-years distant, photon counts are on the order of 10 m-2s{-1]. Pertinent instrumental issues will be discussed
Lloyd James P.
Pierrehumbert Raymond
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