Methane in the atmosphere of the transiting hot Neptune GJ436b?
J.-P. Beaulieu, G. Tinetti, D. M. Kipping, I. Ribas, R. J. Barber, J., Y-K. Cho, I. Polichtchouk, J. Tennyson, S. N. Yurchenko, C. A. Griffith, V., Batista, I. Waldmann, S. Miller, S. Carey, O. Mousis, S. J. Fossey, A., Aylward

TL;DR
This study analyzes multi-wavelength transit observations of GJ436b, combining data with climate models and new molecular line lists, suggesting methane as the dominant absorber in its atmosphere, with implications for atmospheric composition.
Contribution
First comprehensive multi-wavelength transit analysis of GJ436b combining new molecular data and climate models to identify atmospheric constituents.
Findings
Methane likely dominates absorption in GJ436b's atmosphere.
No clear evidence of carbon monoxide or dioxide from transit photometry.
Photometric data compatible with abundant methane, further spectroscopic confirmation needed.
Abstract
We present an analysis of seven primary transit observations of the hot Neptune GJ436b at 3.6, 4.5 and m obtained with the Infrared Array Camera (IRAC) on the Spitzer Space Telescope. After correcting for systematic effects, we fitted the light curves using the Markov Chain Monte Carlo technique. Combining these new data with the EPOXI, HST and ground-based and published observations, the range m can be covered. Due to the low level of activity of GJ436, the effect of starspots on the combination of transits at different epochs is negligible at the accuracy of the dataset. Representative climate models were calculated by using a three-dimensional, pseudo-spectral general circulation model with idealised thermal forcing. Simulated transit spectra of GJ436b were generated using line-by-line radiative transfer models including the opacities of the…
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