Astrochemistry

The Carbon Isotope Ratio Of β Pic b With High-resolution Spectroscopy

By Keith Cowing

Status Report

astro-ph.EP

June 13, 2026

Filed under astro-ph.EP, astronomy, atmosphere, Beta PIctoris, exoplanet, interstellar medium, Protoplanetary Disk, snow line, Spectroscopy, VLT

The Carbon Isotope Ratio Of β Pic b With High-resolution Spectroscopy — Carbon isotope ratio as a function of the semi-major axis for young, directly-imaged companions. Measurements in the HR 8799 system for planets e, b, and c (Ruffio et al. 2026) are shown with squares and connected with a dotted line. The other measurements are for HD 984 b (Costes et al. 2024), GQ Lup b (González Picos et al. 2025b), VHS 1256 b (Gandhi et al. 2023), YSES 1 b (Zhang et al. 2024), AB Pic b (Gandhi et al. 2025), and DH Tau b and HIP 79098 b (Xuan et al. 2024a). The present-day local ISM (12C/13C = 68±14; Milam et al. 2005) and solar photospheric value (12C/13C⊙ = 91.4 ± 1.3; Lyons et al. 2018) are overlaid. The horizontal line spans the typical CO snow-line location for a solar-type host star (22–36 au). For stars hotter than the Sun, the CO snow line is expected at distances greater than 30 au, so β Pic b is located interior to the CO snow line. — astro-ph.EP

Isotopic ratios trace the formation and evolution of planets and link their atmospheres to the chemistry of their natal protoplanetary discs.

We measure ¹²C/¹³C=58+18−15 in the atmosphere of the young super-Jupiter β Pic b from 11 nights of CRIRES+ K-band spectroscopy (≈100,000) at the Very Large Telescope (VLT). We detect both ¹²CO and ¹³CO and constrain ¹²C/¹³C with a Bayesian retrieval jointly fitted with near-infrared photometry.

The inferred ¹²C/¹³C is consistent with the present-day interstellar medium (ISM), is below the solar value, and is comparable to measurements in other young super-Jupiters. We also retrieve T_eff=1629+30−28K, near-solar to mildly super-solar metallicity ([M/H]=0.20+0.16−0.12), a solar-like carbon-to-oxygen ratio (C/O=0.52±0.03), and tentative evidence for thick clouds.

We analyse each night independently and combine the results of the six epochs with the highest signal-to-noise ratio (S/N), propagating night-to-night scatter into the final uncertainties. This provides an isotopic benchmark for a directly imaged planet interior to the CO snow line.

D. González Picos, I.A.G. Snellen, R. Landman, S. de Regt, N. Grasser, J. L. Birkby, T. Stolker, I. Koutalios, M.A. Kenworthy

Comments: Accepted to A&A
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2606.12401 [astro-ph.EP](or arXiv:2606.12401v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2606.12401
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Submission history
From: Darío González Picos
[v1] Wed, 10 Jun 2026 17:58:27 UTC (2,607 KB)
https://arxiv.org/abs/2606.12401
Astrobiology, Astrochemistry,

Keith Cowing

Biologist, Explorers Club Fellow, ex-NASA Space Biologist and Payload integrator, Editor of NASAWatch.com and Astrobiology.com, Lapsed climber, Explorer, Synaesthete, Former Challenger Center board member 🖖🏻

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