First measurement of isotopes in the atmosphere of an exoplanet

An international team of astronomers has become the first in the world to detect isotopes in the atmosphere of an exoplanet. It concerns different forms of carbon in the gas giant planet TYC 8998-760-1 b at a distance of 300 light years in the constellation Musca. The weak signal was measured with ESO’s Very Large Telescope in Chile and seems to indicate that the planet is relatively rich in carbon-13. Astronomers believe this is because the planet formed a great distance from its mother star. The research will be published in the scientific journal Nature on Thursday.

Isotopes are different forms of the same atom, but with varying numbers of neutrons in the nucleus. For example, the six-proton carbon usually has six neutrons (carbon-12), but sometimes seven (carbon-13) or eight (carbon-14). It doesn’t change the chemical properties of carbon much, but isotopes are formed in different ways and often react slightly differently to prevailing conditions. Isotopes are therefore used in a wide range of fields of research: from the detection of cardiovascular disease or cancer to the study of climate change and the determination of the age of fossils and rocks.

Quite special

Astronomers have been able to distinguish carbon-13 from carbon-12 because it absorbs radiation of slightly different colors. “It’s really very special that we can measure this in an exoplanet atmosphere, at such a great distance,” says Leiden Ph.D. student Yapeng Zhang, first author of the article.

Astronomers expected to detect about one in 70 carbon atoms as carbon-13, but for this planet, it appears to be double that. The idea is that the higher carbon 13 is somehow related to the formation of the exoplanet.

Co-author Paul Mollière, of the Max Planck Institute for Astronomy in Heidelberg, Germany, says: “The planet is more than 150 times farther from its mother star than our Earth is from our sun. At such a great distance, the ice may have formed with more carbon-13, causing the highest fraction of this isotope in the planet’s atmosphere today. “

“My exoplanet”

The planet itself, TYC 8998-760-1b, was discovered just two years ago by Leiden Ph.D. student Alexander Bohn, co-author of the article. “It’s great that this discovery was made near ‘my’ planet. It will probably be the first in a long series.”

Ignas Snellen, professor in Leiden and the driving force behind this subject for many years, is above all proud. “It is expected that in the future, isotopes will help further understand exactly how, where and when planets form. This is just the beginning.”