The ~(13)CO-rich atmosphere of a young accreting super-Jupiter

摘要

Isotope abundance ratios have an important role in astronomy and planetary sciences, providing insights into the origin and evolution of the Solar System, interstellar chemistry and stellar nucleosynthesis~(1,2). In contrast to deuterium/hydrogen ratios, carbon isotope ratios are found to be roughly constant (around 89) in the Solar System~(1,3), but do vary on galactic scales with a~(12)C/~(13)C isotopologue ratio of around 68 in the current local interstellar medium~(4-6). In molecular clouds and protoplanetary disks,~(12)CO/~(13)CO ratios can be altered by ice and gas partitioning~(7), low-temperature isotopic ion-exchange reactions~(8)and isotope-selective photodissociation~(9). Here we report observations of~(13)CO in the atmosphere of the young, accreting super-Jupiter TYC 8998-760-1 b, at a statistical significance of more than six sigma. Marginalizing over the planet's atmospheric temperature structure, chemical composition and spectral calibration uncertainties suggests a~(12)CO/~(13)CO ratio of [Formula: see text](90% confidence), a substantial enrichment in~(13)C with respect to the terrestrial standard and the local interstellar value. As the current location of TYC 8998-760-1 b at greater than or equal to 160 astronomical units is far beyond the CO snowline, we postulate that it accreted a substantial fraction of its carbon from ices enriched in~(13)C through fractionation.