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 ¹²C/¹³C isotopologue ratio of around 68 in the current local interstellar medium^4,5,6. In molecular clouds and protoplanetary disks, ¹²CO/¹³CO ratios can be altered by ice and gas partitioning⁷, low-temperature isotopic ion-exchange reactions⁸ and isotope-selective photodissociation⁹. Here we report observations of ¹³CO 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 ¹²CO/¹³CO ratio of \({31}_{-10}^{+17}\)(90% confidence), a substantial enrichment in ¹³C 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 ¹³C through fractionation.

同位素丰度比在天文学和行星科学中发挥着重要作用，可以深入了解太阳系的起源和演化、星际化学和恒星核合成^1,2。与氘/氢比率相比，发现太阳系中的碳同位素比率大致恒定（约 89）^1,3，但在银河系尺度上确实有所不同，目前¹² C/ ¹³ C 同位素比约为 68本地星际介质^4,5,6。在分子云和原行星盘中，¹² CO/ ¹³ CO 的比率可以通过冰和气体的分配⁷、低温同位素离子交换反应^8来改变和同位素选择性光解⁹。在这里，我们报告了对年轻的、吸积的超级木星 TYC 8998-760-1 b 大气中^{13 CO 的观测，其统计显着性超过 6 sigma。}对行星大气温度结构、化学成分和光谱校准不确定性的边缘化表明¹² CO/ ¹³ CO 比率为\({31}_{-10}^{+17}\)（90% 置信度），在¹³C相对于地面标准和当地星际值。由于目前 TYC 8998-760-1 b 的位置大于或等于 160 个天文单位，远远超出了 CO 雪线，我们假设它通过分馏从富含¹³ C 的冰中吸收了相当大一部分的碳。