Giant Planet Reveals Its Birth Secrets Through a Rare Molecule express
In the attic, you find an old, worn suitcase. From the stickers and scratches, you can guess where it's been. Astronomers have long searched for a similar 'sticker' for planets, and thought they found it in carbon monoxide molecules. Ordinary carbon monoxide consists of a carbon-12 atom and an oxygen atom. But sometimes a rare version appears — with carbon-13, which has one extra neutron in its nucleus. Previously, it was thought that if a planet gathered a lot of this 'heavy' gas, it must have formed far from its star, beyond the snow line, where ice froze. If little — closer to the star.
A team of astronomers decided to test this idea in practice. They targeted the planet β Pictoris b — a massive gas giant that can be seen directly through a telescope, not just by indirect signs. The planet is bright, so its signal is captured clearly. Using the upgraded GRAVITY+ instrument on the Very Large Telescope in Chile, they obtained a spectrum with a record signal-to-noise ratio — up to 60 per wavelength point. A spectrum is light split by color, where each molecule leaves its own 'fingerprint'.
And here came the surprise. The rare molecule with carbon-13 was found, but its abundance was utterly ordinary — about 1 in 91. Just like in the Sun, just like in interstellar clouds. No hint of special birth conditions. It turns out the old 'compass' doesn't always point in the right direction. The authors suggest that carbon-13 might mix within the disk, or that the planet gathered gas from different parts of it.
Moreover, the observations lasted a full seven hours, and the scientists tried to detect whether the planet's atmosphere changes over time. They caught a faint hint: the brightness fluctuated slightly, by about one and a half percent. Perhaps clouds drifted by, or something changed in the chemical composition. But it's too early to say for sure — new observations are needed. So the suitcase with stickers told us less than hoped, and astronomers are now seeking more reliable ways to look into the past of distant worlds.
Original abstract
as written by the authors arXiv:2606.11972
The $$^{12}$$CO/$$^{13}$$CO ratio was introduced as an indicator for where in the disk a planet has formed. Previously a lower value compared to the host star's was suggested to show that a planet accreted CO ice beyond the disk's CO ice line. In this letter we aim to determine the $$^{12}$$CO/$$^{13}$$CO value of the directly imaged planet $$\beta$$ Pictoris b, and whether we can link it to its formation. Its apparent brightness results in an exceptional S/N of up to ~60 per wavelength point. We present the first science observations with the upgraded GRAVITY+ instrument at a spectral resolution of R ~ 4000, which we analyse with petitRADTRANS. Our retrievals robustly indicate the presence of $$^{13}$$CO with a $$^{12}$$CO/$$^{13}$$CO ratio of 91$$^{+24}_{-17}$$, consistent with both a solar to ISM-like value. Our $$^{12}$$CO/$$^{13}$$CO value corroborates recent interpretations that $$^{13}$$CO may be a less useful tracer of formation location in the disk than previously thought; nonetheless, we discuss theories with which this value is consistent. As our observations span ~7 hours, this enabled us to search for atmospheric variability in $$\beta$$ Pictoris b; we report a tentative constraint on the variability amplitude of about 1.4$$^{+0.6}_{-0.7}$$%.
Carbon monoxide (CO) is the second most abundant molecule in the universe after hydrogen. It's used as a 'thermometer' for cold regions of space because it glows in the radio range even at temperatures close to absolute zero.
In Stanisław Lem's novel 'Solaris', the planet's ocean changed its structure to adapt to observations. Astronomers seek similar variability in real exoplanet atmospheres, so far, only a hint of brightness fluctuations of one and a half percent.