Astronomers using ESO’s Very Large Telescope have detected the isotopically substituted carbon monoxide, 13CO, in the atmosphere of the young giant exoplanet TYC 8998-760-1b.
Schematics of the observations of TYC 8998-760-1b using SINFONI on ESO’s Very Large Telescope. The background image is captured by the SPHERE instrument on the Very Large Telescope. The small blue box marks the field of view of SINFONI observations targeting TYC 8998-760-1b. Both the host star and TYC 8998-760-1c are outside the field of view. An example of the wavelength-collapsed image is shown in the enlarged blue box, showing negligible contribution from starlight. Image credit: ESO / Bohn et al. / Zhang et al.
Also known as 2MASS J13251211-6456207, the star is about the same mass as our Sun, but is only 16.7 million years old.
It hosts two planets, TYC 8998-760-1b and c, at least 14 and 6 times more massive than Jupiter.
They orbit their parent star at distances of 160 and 320 AU; this places the planets much further away from their star than Jupiter or Saturn are from the Sun.
“Isotopes are different forms of the same atom, but with a varying number of neutrons in the nucleus,” said Yapeng Zhang, a Ph.D. candidate at Leiden Observatory, and colleagues.
“For example, carbon with six protons typically has six neutrons (carbon-12), but occasionally seven (carbon-13) or eight (carbon-14).”
“This does not change much the chemical properties of carbon, but isotopes are formed in different ways and often react slightly differently to the prevailing conditions.”
In the new study, the astronomers observed TYC 8998-760-1b on two nights, June 5 and June 19, 2019, using the Spectrograph for INtegral Field Observations in the Near Infrared (SINFONI) instrument installed on ESO’s Very Large Telescope.
They were able to distinguish carbon-13 from carbon-12 because it absorbs radiation at slightly different colors.
“It is really quite special that we can measure this in an exoplanet atmosphere, at such a large distance,” Zhang said.
“We expected to detect about one in 70 carbon atoms to be carbon-13, but for this planet, it seems to be twice as much.”
“The idea is that the higher carbon-13 is somehow related to the formation of the exoplanet.”
“The planet is more than one hundred and fifty times further away from its parent star than our Earth is from our Sun,” said Dr. Paul Mollière, an astronomer at the Max Planck Institute for Astronomy.
“At such a great distance, ices have possibly formed with more carbon-13, causing the higher fraction of this isotope in the planet’s atmosphere today.”
“The expectation is that in the future isotopes will further help to understand exactly how, where and when planets form. This is just the beginning,” said Professor Ignas Snellen, an astronomer at Leiden Observatory.
The team’s paper was published in the journal Nature.
Y. Zhang et al. 2021. The 13CO-rich atmosphere of a young accreting super-Jupiter. Nature 595, 370-372; doi: 10.1038/s41586-021-03616-x