Identification of carbon dioxide in an exoplanet atmosphere

Abstract

Carbon dioxide (CO2) is a key chemical species that is found in a wide range of planetary atmospheres. In the context of exoplanets, CO2 is an indicator of the metal enrichment (that is, elements heavier than helium, also called ‘metallicity’)1–3, and thus the formation processes of the primary atmospheres of hot gas giants4–6. It is also one of the most promising species to detect in the secondary atmospheres of terrestrial exoplanets7–9. Previous photometric measurements of transiting planets with the Spitzer Space Telescope have given hints of the presence of CO2, but have not yielded definitive detections owing to the lack of unambiguous spectroscopic identification10–12. Here we present the detection of CO2 in the atmosphere of the gas giant exoplanet WASP-39b from transmission spectroscopy observations obtained with JWST as part of the Early Release Science programme13,14. The data used in this study span 3.0–5.5 micrometres in wavelength and show a prominent CO2 absorption feature at 4.3 micrometres (26-sigma significance). The overall spectrum is well matched by one-dimensional, ten-times solar metallicity models that assume radiative–convective–thermochemical equilibrium and have moderate cloud opacity. These models predict that the atmosphere should have water, carbon monoxide and hydrogen sulfide in addition to CO2, but little methane. Furthermore, we also tentatively detect a small absorption feature near 4.0 micrometres that is not reproduced by these models.

Theoretical study of the CO2–O2 van der Waals complex: potential energy surface and applications

“…In a planetary atmosphere, CO 2 acts both as a powerful greenhouse gas and as a coolant, strongly influencing the formation and evolution of primary and secondary atmospheres of hot gas giants and terrestrial planets. 1,2 Very recently, CO 2 has been detected in transmission spectra in the atmosphere of the gas giant exoplanet WASP-39b, 3 confirming the hints of earlier photometric detections of CO 2 during transits. 4 Accurate photochemical modeling of CO 2 -rich atmospheres of exoplanets will require detailed descriptions of thermophysical properties of carbon dioxide and other atmospheric species, such as dioxygen molecules.…”

Early Release Science of the exoplanet WASP-39b with JWST NIRISS

“…Implementations of this procedure to the JWST data include ref. 109 . For a given set of planetary parameters, our methods precompute the temperature–pressure structure of the planetary atmosphere and the thermochemical equilibrium gas-mixing-ratio profiles.…”

“…The transmission spectrum of the planet is computed with CHIMERA 104 , 111 – 115 using the converged atmospheric structures. We compare the observations to these models in a Bayesian inference framework using the nested sampling algorithm MultiNest 108 through its Python implementation PyMultiNest 109 and obtain an optimal set of M/H, C/O ratio, K/O ratio and f through nearest-neighbour search in the grid. When computing the transmission spectrum for a given set of (M/H, C/O ratio, K/O ratio, f ), we also adjust the 1-bar planetary radius controlling the absolute transit depth (an arbitrary pressure with no direct impact on the inferred properties; see, for example, ref.…”

Traveling Planetary-scale Waves Cause Cloud Variability on Tidally Locked Aquaplanets

“…We omit the dry case because it has no timevarying atmospheric chemistry or clouds. The NIRSpec instrument's range covers water vapor features in the infrared at 1.4, 1.8, and 2.7 μm, as well as CO 2 features at 2.1, 2.7, and 4.3 μm (Ahrer et al 2023). For each simulated atmosphere, we prescribe the orbital, planetary, and stellar parameters shown in Table 1, together with the pressure, temperature, altitude, H 2 O, N 2 , and CO 2 data from the UM.…”