GJ 436b is a warm-- approximately 800 K--extrasolar planet that periodically eclipses its low-mass (half the mass of the Sun) host star, and is one of the few Neptune-mass planets that is amenable to detailed characterization. Previous observations have indicated that its atmosphere has a methane-to-CO ratio that is 100,000 times smaller than predicted by models for hydrogen-dominated atmospheres at these temperatures. A recent study proposed that this unusual chemistry could be explained if the planet's atmosphere is significantly enhanced in elements heavier than H and He. In this study we present complementary observations of GJ 436b's atmosphere obtained during transit. Our observations indicate that the planet's transmission spectrum is effectively featureless, ruling out cloud-free, hydrogen-dominated atmosphere models with an extremely high significance of 48 sigma. The measured spectrum is consistent with either a high cloud or haze layer located at a pressure of approximately 1 mbar or with a relatively hydrogen-poor (three percent hydrogen and helium mass fraction) atmospheric composition.
@article{arxiv.1401.3350,
title = {A featureless transmission spectrum for the Neptune-mass exoplanet GJ 436b},
author = {Heather A. Knutson and Björn Benneke and Drake Deming and Derek Homeier},
journal= {arXiv preprint arXiv:1401.3350},
year = {2015}
}
Comments
23 pages, 12 figures, published in Nature 505, 66 (2014)