2013/12/23 by Heather A. Knutson, Björn Benneke, Drake Deming +2 · 4 citations
Physics and Astronomy · #Astro and Planetary Science #Astrobiology #Astronomy #Astrophysics #Astrophysics and Star Formation Studies #Computer science #Exoplanet #Neptune #Physics #Planet #Quantum mechanics #Spectrum (functional analysis) #Stellar, planetary, and galactic studies #Telecommunications #Transmission (telecommunications) #astro-ph.EP
paper · pdf · doi:10.1038/nature12887
23 pages, 12 figures, published in Nature 505, 66 (2014)
openalex publication_date 2013/12/23 · arxiv created 2014/01/14 · arxiv updated 2015/06/18 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
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.