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Signatures of Nitrogen Chemistry in Hot Jupiter Atmospheres

Accepted version
Peer-reviewed

Type

Article

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Abstract

Inferences of molecular compositions of exoplanetary atmospheres have generally focused on C, H, and O-bearing molecules. Recently, additional absorption in HST WFC3 transmission spectra around 1.55μm has been attributed to nitrogen-bearing chemical species: NH3 or HCN. These species, if present in significant abundance, would be strong indicators of disequilibrium chemical processes -- e.g. vertical mixing and photochemistry. The derived N abundance, in turn, could also place important constraints on planetary formation mechanisms. Here, we examine the detectability of nitrogen chemistry in exoplanetary atmospheres. In addition to the WFC3 bandpass (1.1-1.7μm), we find that observations in K-band at $\sim2.2\mum,achievablewithpresentgroundbasedtelescopes,sampleastrongNH_3$ feature, whilst observations at $\sim3.1\mu$m and $\sim4.0\mumsamplestrongHCNfeatures.Inanticipationofsuchobservations,wepredictabsorptionfeatureamplitudesduetonitrogenchemistryinthe1−5\mumspectralrangepossibleforatypicalhotJupiter.Finally,weconductatmosphericretrievalsof9hotJupitertransmissionspectrainsearchofnearinfraredabsorptionfeaturessuggestiveofnitrogenchemistry.WereportweakdetectionsofNH_3$ in WASP-31b (2.2σ), HCN in WASP-63b (2.3σ), and excess absorption that could be attributed to NH3 in HD 209458b. High-precision observations from 1-5μm (e.g., with the James Webb Space Telescope), will enable definitive detections of nitrogen chemistry, in turn serving as powerful diagnostics of disequilibrium atmospheric chemistry and planetary formation processes.

Description

Keywords

methods: data analysis, planets and satellites: atmospheres, techniques: spectroscopic

Journal Title

Astrophysical Journal Letters

Conference Name

Journal ISSN

2041-8205
2041-8213

Volume Title

850

Publisher

American Astronomical Society
Sponsorship
Science and Technology Facilities Council (ST/N000927/1)
Science and Technology Facilities Council (1638355)