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Title: Three Possible Origins for the Gas Layer on GJ 1214b
Authors: L. A. Rogers, S. Seager
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We present an analysis of the bulk composition of the MEarth transiting super Earth exoplanet GJ 1214b using planet interior structure models. We consider three possible origins for the gas layer on GJ 1214b: direct accretion of gas from the protoplanetary nebula, sublimation of ices, and outgassing from rocky material. Armed only with measurements of the planet mass (M_p=6.550.98 M_{earth}), radius (R_p=2.6780.13 R_{earth}), and stellar irradiation level, our main conclusion is that we cannot infer a unique composition. A diverse range of planet interiors fits the measured planet properties. Nonetheless, GJ 1214b's relatively low average density (rho_p=1870400 kg m^{-3}) means that it almost certainly has a significant gas component. Our second major conclusion is that under most conditions we consider GJ 1214b would not have liquid water. Even if the outer envelope is predominantly sublimated water ice, the envelope will likely consist of a super-fluid layer sandwiched between vapor above and plasma (electrically conductive fluid) below at greater depths. In our models, a low intrinsic planet luminosity (<~2TW) is needed for a water envelope on GJ 1214b to pass through the liquid phase.

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GJ 1214 b
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The new-found world, GJ1214b, is about 6.5 times as massive as the Earth. Its host star, GJ1214, is a small, red type M star about one-fifth the size of the Sun. It has a surface temperature of only about 4,900 degrees F and a luminosity only three-thousandths as bright as the Sun.
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Charbonneau Exoplanet Research Team

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GJ 1214b
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Title: The Nature of the Atmosphere of the Transiting Super-Earth GJ 1214b
Authors: E. Miller-Ricci, J. J. Fortney

The newly discovered planet GJ 1214b is the first known transiting super-Earth requiring a significant atmosphere to explain its observed mass and radius. Models for the structure of this planet predict that it likely possesses a H-He envelope of at least 0.05% of the total mass of the planet. However, models without a significant H-He atmosphere are not entirely ruled out by the available data. Here we explore a range of possible atmospheres for the planet, ranging from solar composition gas, to pure CO_2 or water (steam). We present transmission and emission spectra for each of these cases. We find that, if GJ 1214b possesses a hydrogen-rich atmosphere as expected, then the primary transit depth for such an atmosphere would vary at a level of up to 0.3% as a function of wavelength, relative to the background light of its M-dwarf host star. Observations at this level of precision are potentially obtainable with current space-based instrumentation. Successful detection of the transmission signature of this planet at the ~0.1% level would therefore provide confirmation of the hydrogen-rich nature of the planetary atmosphere. It follows that transmission spectroscopy at this level of precision could provide a first glimpse into answering the question of whether planets in the super-Earth mass regime (1 - 10 M_Earth) more closely resemble large terrestrial planets or small gas giant planets.

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