Identification of carbon dioxide in an exoplanet atmosphere

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’), and thus the formation processes of the primary atmospheres of hot gas giants. It is also one of the most promising species to detect in the secondary atmospheres of terrestrial exoplanets. 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 identification. 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 programme. 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

A High Spatial and Spectral Resolution Study of Jupiter’s Mid-infrared Auroral Emissions and Their Response to a Solar Wind Compression

We present mid-infrared spectroscopy of Jupiter's mid-to-high latitudes using the Gemini-North/Texas Echelon Cross Echelle Spectrograph on 2017 March 17–19. These observations capture Jupiter's hydrocarbon auroral emissions before, during, and after the arrival of a solar wind compression on March 18, which highlights the coupling between the polar stratosphere and external space environment. In comparing observations on March 17 and 19, we observe a brightening of the CH4, C2H2, and C2H4 emission in regions spatially coincident with the northern duskside main auroral emission (MAE). In inverting the spectra to derive atmospheric information, we determine that the duskside brightening results from upper stratospheric (p 200 km) heating (e.g., ΔT = 9.1 ± 2.1 K at 9 μbar at 67fdg5N, 162fdg5W) with negligible heating at deeper pressures. Our interpretation is that the arrival of the solar wind enhancement drove magnetospheric dynamics through compression and/or viscous interactions on the flank. These dynamics accelerated currents and/or generated higher Poynting fluxes, which ultimately warmed the atmosphere through Joule heating and ion-neutral collisions. Poleward of the southern MAE, temperature retrievals demonstrate that auroral-related heating penetrates as deep as the 10 mbar level, in contrast to poleward of the northern MAE, where heating is only observed as deep as ∼3 mbar. We suggest that this results from the south having higher Pedersen conductivities and therefore stronger currents and acceleration of the neutrals, as well as the poleward heating overlapping with the apex of Jupiter's circulation, thereby inhibiting efficient horizontal mixing/advection.</p