Detectable Abundance of Cyanoacetylene (HC${}_3$N) Predicted on Reduced Nitrogen-Rich Super-Earth Atmospheres

Abstract

We predict that cyanoacetylene (HC${}_3$N) is produced photochemically in the atmosphere of GJ 1132 b in abundances detectable by the James Webb Space Telescope (JWST), assuming that the atmosphere is hydrogen dominated and rich in molecular nitrogen (N${}_2$), methane (CH${}_4$) and hydrogen cyanide (HCN), as described by Swain et al. (2021). First, we construct line list and cross-sections for HC${}_3$N. Then we apply these cross-sections and the model atmosphere of Swain et al. (2021) to a radiative transfer model in order to simulate the transmission spectrum of GJ 1132 b as it would be seen by JWST, accounting for the uncertainty in the retrieved abundances. We predict that cyanoacetylene features at various wavelengths, with a clear lone feature at 4.5 $\mu$m, observable by JWST after one transit. This feature persists within the $1-\sigma$ uncertainty of the retrieved abundances of HCN and CH${}_4$. The signal is detectable for stratospheric temperatures $\lesssim 600$ K and moderate stratospheric mixing ($10^6\mathrm{c}{\mathrm{m}}^2{\mathrm{s}}^{-1}\lesssim K_{zz}\lesssim 10^8\mathrm{c}{\mathrm{m}}^2{\mathrm{s}}^{-1}$). Our results also indicate that HC${}_3$N is an important source of opacity that future retrieval models should consider.

arXiv comment11 pages, 5 figures, accepted for publication in ApJL, comments welcome

References in corpus (17)

• petitRADTRANS: a Python radiative transfer package for exoplanet characterization and retrieval
• PandExo: A Community Tool for Transiting Exoplanet Science with JWST & HST
• Detection of an atmosphere around the super-Earth 55 Cancri e
• ExoCross: a general program for generating spectra from molecular line lists
• Predictions of the atmospheric composition of GJ 1132b
• A Chemical Kinetics Network for Lightning and Life in Planetary Atmospheres
• Hydrogen Cyanide in Nitrogen-Rich Atmospheres of Rocky Exoplanets
• The terrestrial late veneer from core disruption of a lunar-sized impactor
• Ground-based optical transmission spectroscopy of the small, rocky exoplanet GJ 1132b
• Detection of an Atmosphere on a Rocky Exoplanet
• ARES V: No Evidence For Molecular Absorption in the HST WFC3 Spectrum of GJ 1132 b
• Abundance Measurements of Titan's Stratospheric HCN, HC${}_3$N, C${}_3$H${}_4$, and CH${}_3$CN from ALMA Observations
• Detection of the atmosphere of the 1.6 Earth mass exoplanet GJ 1132b
• Redox hysteresis of super-Earth exoplanets from magma ocean circulation
• Spectral binning of precomputed correlated-k coefficients
• Atmospheric compositions and observability of nitrogen dominated ultra-short period super-Earths
• Rotational and high-resolution infrared spectrum of HC${}_3$N: global ro-vibrational analysis and improved line catalogue for astrophysical observations

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