A ground-based near-infrared emission spectrum of the exoplanet HD 189733b

Mark R. Swain, Pieter Deroo, Caitlin A. Griffith, Giovanna Tinetti, Azam Thatte, Gautam Vasisht, Pin Chen, Jeroen Bouwman, Ian J. Crossfield, Daniel Angerhausen, Cristina Afonso, Thomas Henning

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Abstract

Detection of molecules using infrared spectroscopy probes the conditions and compositions of exoplanet atmospheres. Water (H2 O), methane (CH4), carbon dioxide (CO2), and carbon monoxide (CO) have been detected in two hot Jupiters. These previous results relied on space-based telescopes that do not provide spectroscopic capability in the 2.4-5.2 μm spectral region. Here we report ground-based observations of the dayside emission spectrum for HD 189733b between 2.0-2.4 μm and 3.1-4.1 μm, where we find a bright emission feature. Where overlap with space-based instruments exists, our results are in excellent agreement with previous measurements. A feature at ∼ 3.25 μm is unexpected and difficult to explain with models that assume local thermodynamic equilibrium (LTE) conditions at the 1 bar to 1 ×-10-6 bar pressures typically sampled by infrared measurements. The most likely explanation for this feature is that it arises from non-LTE emission from CH4, similar to what is seen in the atmospheres of planets in our own Solar System. These results suggest that non-LTE effects may need to be considered when interpreting measurements of strongly irradiated exoplanets.

Original languageEnglish (US)
Pages (from-to)637-639
Number of pages3
JournalNature
Volume463
Issue number7281
DOIs
StatePublished - Feb 4 2010

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    Swain, M. R., Deroo, P., Griffith, C. A., Tinetti, G., Thatte, A., Vasisht, G., Chen, P., Bouwman, J., Crossfield, I. J., Angerhausen, D., Afonso, C., & Henning, T. (2010). A ground-based near-infrared emission spectrum of the exoplanet HD 189733b. Nature, 463(7281), 637-639. https://doi.org/10.1038/nature08775