Observability of molecular species in a nitrogen dominated atmosphere for 55 Cancri e

TL;DR

This study investigates the potential nitrogen-dominated atmosphere of exoplanet 55 Cancri e, analyzing its composition and spectral features to guide future observational efforts with telescopes like JWST.

Contribution

It provides the first detailed analysis of a nitrogen-rich atmospheric composition for 55 Cancri e, including spectral predictions and the impact of N/O ratios.

Findings

NH3 and HCN show strong spectral features in transmission.

CO and HCN dominate emission spectra.

N/O ratio influences water and carbon compound features.

Abstract

One of the key goals of exoplanet science is the atmospheric characterisation of super-Earths. Atmospheric abundances provide insight on the formation and evolution of those planets and help to put our own rocky planets in context. Observations on 55 Cancri e point towards a N-dominated atmosphere. In this paper we explore this possibility, showing which will be the most abundant gases and observable species in emission and transmission spectroscopy of such an atmosphere. We use analytical arguments and observed parameters to estimate the possible thermal profile of the atmosphere and test three different extreme possibilities. The chemistry is calculated using equilibrium calculations and adopting Titan's elemental abundances as a potential N-dominated atmospheric composition. We also test the effect of different N/O ratios in the atmosphere. Emission and transmission spectra are computed and showed with a resolution relevant to future missions suitable to observe super-Earths (e.g. JWST, ARIEL). We find that even though N$_2$ is the most abundant molecule in the atmosphere followed by H$_2$ and CO, the transmission spectra shows strong features of NH3 and HCN, and CO and HCN dominate emission spectra. We also show that a decrease in the N/O ratio leads to stronger H2O, CO and CO2 and weaker NH3 and HCN features. A larger N/O is also more consistent with observations. Our exploration of a N-atmosphere for 55 Cancri e serve as a guide to understand such atmospheres and provide a reference for future observations.