Astronomy and Astrophysics – Astrophysics – Earth and Planetary Astrophysics
Scientific paper
2010-02-12
Nature, Volume 463, Issue 7281, pp. 637-639 (2010)
Astronomy and Astrophysics
Astrophysics
Earth and Planetary Astrophysics
12 pages, 2 figures, published in Nature
Scientific paper
Detection of molecules using infrared spectroscopy probes the conditions and compositions of exoplanet atmospheres. Water (H2O), 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 micron spectral region. Here we report ground-based observations of the dayside emission spectrum for HD 189733b between 2.0-2.4 micron and 3.1-4.1 micron, 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 micron is unexpected and difficult to explain with models that assume local thermodynamic equilibrium (LTE) conditions at the 1 bar to 1 x 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.
Afonso Cristina
Angerhausen Daniel
Bouwman Jeroen
Chen Pin
Crossfield Ian J.
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