Signatures of Nitrogen Chemistry in Hot Jupiter Atmospheres

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 1.55$\mu$m has been attributed to nitrogen-bearing chemical species: NH${}_3$ 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 (1.1-1.7$\mu$m), we find that observations in K-band at $\sim$2.2$\mu$m, achievable with present ground-based telescopes, sample a strong NH${}_3$ feature, whilst observations at $\sim$3.1$\mu$m and $\sim$4.0$\mu$m sample strong HCN features. In anticipation of such observations, we predict absorption feature amplitudes due to nitrogen chemistry in the 1-5$\mu$m spectral range possible for a typical hot Jupiter. Finally, we conduct atmospheric retrievals of 9 hot Jupiter transmission spectra in search of near-infrared absorption features suggestive of nitrogen chemistry. We report weak detections of NH${}_3$ in WASP-31b (2.2$\sigma$), HCN in WASP-63b (2.3$\sigma$), and excess absorption that could be attributed to NH${}_3$ in HD 209458b. High-precision observations from 1-5$\mu$m (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.

9 pages, 5 figures. Accepted for publication in ApJL

References in corpus (12)

• The imprint of exoplanet formation history on observable present-day spectra of hot Jupiters
• Towards Chemical Constraints on Hot Jupiter Migration
• Ground-based detection of sodium in the transmission spectrum of exoplanet HD209458b
• A chemical model for the atmosphere of hot Jupiters
• HST hot-Jupiter transmission spectral survey: detection of potassium in WASP-31b along with a cloud deck and Rayleigh scattering
• A consistent retrieval analysis of 10 Hot Jupiters observed in transmission
• Detection of titanium oxide in the atmosphere of a hot Jupiter
• H2O abundances in the atmospheres of three hot Jupiters
• GENESIS: New Self-Consistent Models of Exoplanetary Spectra
• Near-infrared transmission spectrum of the warm-uranus GJ 3470b with the Wide Field Camera-3 on the Hubble Space Telescope
• The Role of Ice Compositions for Snowlines and the C/N/O Ratios in Active Disks
• GTC OSIRIS transiting exoplanet atmospheric survey: detection of potassium in HAT-P-1b from narrowband spectrophotometry

Cited by in corpus (31)

• Tracing the formation history of giant planets in protoplanetary disks with Carbon, Oxygen, Nitrogen and Sulphur
• Beyond Equilibrium Temperature: How the Atmosphere/Interior Connection Affects the Onset of Methane, Ammonia, and Clouds in Warm Transiting Giant Planets
• Atmospheric Regimes and Trends on Exoplanets and Brown Dwarfs
• On degeneracies in retrievals of exoplanetary transmission spectra
• The ARCiS framework for Exoplanet Atmospheres: Modelling Philosophy and Retrieval
• Molecular Cross Sections for High Resolution Spectroscopy of Super Earths, Warm Neptunes and Hot Jupiters
• JWST transmission spectroscopy of HD 209458b: a super-solar metallicity, a very low C/O, and no evidence of CH4, HCN, or C2H2
• Grid of Pseudo-2D Chemistry Models for Tidally-Locked Exoplanets. I. The Role of Vertical and Horizontal Mixing
• On The Compatibility of Ground-based and Space-based Data: WASP-96 b, An Example
• The Metal-Rich Atmosphere of the Neptune HAT-P-26b
• Stellar surface inhomogeneities as a potential source of the atmospheric signal detected in the K2-18 b transmission spectrum
• Photochemistry in hot H2-dominated exoplanet atmospheres
• Outstanding Challenges of Exoplanet Atmospheric Retrievals
• The composition of hot Jupiter atmospheres assembled within chemically evolved protoplanetary discs
• A chemical kinetics code for modelling exoplanetary atmospheres
• Nitrogen as a Tracer of Giant Planet Formation. I.: A Universal Deep Adiabatic Profile and Semi-analytical Predictions of Disequilibrium Ammonia Abundances in Warm Exoplanetary Atmospheres
• The role of clouds on the depletion of methane and water dominance in the transmission spectra of irradiated exoplanets
• HCN production in Titan's Atmosphere: Coupling quantum chemistry and disequilibrium atmospheric modeling
• Evidence of a Clear Atmosphere for WASP-62b: the Only Known Transiting Gas Giant in the JWST Continuous Viewing Zone
• Understanding the atmospheric properties and chemical composition of the ultra-hot Jupiter HAT-P-7b II. Mapping the effects of gas kinetics
• Evidence for chromium hydride in the atmosphere of Hot Jupiter WASP-31b
• Transmission spectroscopy of WASP-52 b with JWST NIRISS: Water and helium atmospheric absorption, alongside prominent star-spot crossings
• Molecular tracers of planet formation in the atmospheres of hot Jupiters
• The Molecular Composition of Shadowed Protosolar Disk Midplanes beyond the Water Snowline
• Colour-magnitude diagrams of transiting Exoplanets -- III. A public code, nine strange planets, and the role of Phosphine
• Ground-based HCN submillimetre measurements in Titan's atmosphere: an intercomparison with Herschel observations
• Toward a multidimensional analysis of transmission spectroscopy. Part III: Modelling 2D effects in retrievals with TauREx
• A Detailed Investigation of HD 209458 b HST & JWST Transmission Spectra with SANSAR
• The SPACE Program. I. The featureless spectrum of HD 86226 c challenges sub-Neptune atmosphere trends
• Experimental Investigation of the Photochemical Production of Hydrocarbons in Warm Gas Giant Exoplanet Atmospheres
• Interpreting the atmospheric composition of exoplanets: sensitivity to planet formation assumptions