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Ahrer, E. M., Alderson, L., Batalha, N. M., Batalha, N. E., Bean, J. L., Beatty, T. G., et al. (2023). Identification of carbon dioxide in an exoplanet atmosphere. Nature, Early Access.
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 giants(4-6). It is also one of the most promising species to detect in the secondary atmospheres of terrestrial exoplanets(7-9). 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 identification(10-12). 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 programme(13,14). The data used in this study span 3.0-5.5micrometres in wavelength and show a prominent CO2 absorption feature at 4.3micrometres (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 4.0micrometres that is not reproduced by these models.
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Kalyaan, A., Pinilla, P., Krijt, S., Mulders, G. D., & Banzatti, A. (2021). Linking Outer Disk Pebble Dynamics and Gaps to Inner Disk Water Enrichment. Astrophys. J., 921(1), 84.
Abstract: Millimeter continuum imaging of protoplanetary disks reveals the distribution of solid particles and the presence of substructures (gaps and rings) beyond 5-10 au, while infrared (IR) spectra provide access to abundances of gaseous species at smaller disk radii. Building on recent observational findings of an anti-correlation between the inner disk water luminosity and outer dust disk radius, we aim here at investigating the dynamics of icy solids that drift from the outer disk and sublimate their ice inside the snow line, enriching the water vapor that is observed in the IR. We use a volatile-inclusive disk evolution model to explore a range of conditions (gap location, particle size, disk mass, and alpha viscosity) under which gaps in the outer disk efficiently block the inward drift of icy solids. We find that inner disk vapor enrichment is highly sensitive to the location of a disk gap, yielding for each particle size a radial “sweet spot” that reduces the inner disk vapor enrichment to a minimum. For pebbles of 1-10 mm in size, which carry the most mass, this sweet spot is at 7-15 au, suggesting that inner gaps may have a key role in reducing ice delivery to the inner disk and may not allow the formation of Earths and super-Earths. This highlights the importance of observationally determining the presence and properties of inner gaps in disks. Finally, we argue that the inner water vapor abundance can be used as a proxy for estimating the pebble drift efficiency and mass flux entering the inner disk.
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