Atmospheres & Climate

JWST Measurements Of 13C, 18O and 17O In The Atmosphere Of Super-Jupiter VHS 1256 b

By Keith Cowing
Status Report
November 10, 2023
Filed under , , , , , , , , ,
JWST Measurements Of 13C, 18O and 17O In The Atmosphere Of Super-Jupiter VHS 1256 b
Top Panel: Best fitting model from the retrieval, along with the data points of the NIRSpec G395H/F290LP detector 2 (NRS2) observations of VHS 1256 b. We also show the 1σ range of the residuals of the data and model. Bottom Panel: Residuals of the best fit model and the observations, with the 1, 2 and 3σ ranges shown in grey. — astro-ph.EP

Isotope ratios have recently been measured in the atmospheres of directly-imaged and transiting exoplanets from ground-based observations. The arrival of JWST allows us to characterise exoplanetary atmospheres in further detail and opens up wavelengths inaccessible from the ground.

In this work we constrain the carbon and oxygen isotopes 13C, 18O and 17O from CO in the atmosphere of the directly-imaged companion VHS 1256 b through retrievals of the ∼4.1-5.3 μm NIRSpec G395H/F290LP observations from the early release science programme (ERS 1386). We detect and constrain 13C16O, 12C18O and 12C17O at 32, 16 and 10σ confidence respectively, thanks to the very high signal-to-noise observations.

We find the ratio of abundances are more precisely constrained than their absolute values, with 12C/13C=62+2−2, in between previous measurements for companions (∼30) and isolated brown dwarfs (∼100). The oxygen isotope ratios are 16O/18O=425+33−28 and 16O/17O=1010+120−100. All of the ratios are lower than the local inter-stellar medium and Solar System, suggesting that abundances of the more minor isotopes are enhanced compared to the primary. This could be driven by isotope fractionation in protoplanetary disks, which can potentially alter the carbon and oxygen ratios through isotope selective photodissociation, gas/ice partitioning and isotopic exchange reactions.

In addition to CO, we constrain 1H216O and 12C16O2 (the primary isotopologues of both species), but find only upper limits on 12C1H4 and 14N1H3. This work highlights the power of JWST to constrain isotopes in exoplanet atmospheres, with great promise in determining formation histories in the future.

Siddharth Gandhi, Sam de Regt, Ignas Snellen, Yapeng Zhang, Benson Rugers, Niels van Leur, Quincy Bosschaart

Comments: 11 pages, 7 figures, 2 tables, accepted for publication in The Astrophysical Journal Letters
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2311.05349 [astro-ph.EP] (or arXiv:2311.05349v1 [astro-ph.EP] for this version)
Submission history
From: Siddharth Gandhi
[v1] Thu, 9 Nov 2023 13:21:25 UTC (812 KB)
Astrobiology, Astrochemistry,

Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) 🖖🏻