Individual isotopes measured in exoplanet atmosphere for first time
Astronomers have counted the number of neutrons inside carbon atoms from 2.8 quadrillion km away. The team managed to measure the ratios of carbon isotopes in the atmosphere of an exoplanet for the first time, which can tell us about how it formed.
Atoms of a specific element can have different amounts of neutrons in their nuclei, resulting in different types that we call isotopes. Carbon for instance has 15 isotopes, of which carbon-12 and carbon-13 are the most stable and common in nature. Measuring the ratios of isotopes can help us date fossils, track climate change, and check for biomarkers of disease.
Beyond Earth, scientists have measured isotopes as far away as the Moon and Mars, but now that distance has been extended to a planet outside the solar system. The planet in question is a super-Jupiter called Tycho 8998-760-1 b, located about 300 light-years away in the constellation Musca.
Using the Very Large Telescope in Chile, the researchers analyzed the spectrum of light from the host star passing through the planet’s atmosphere. Different elements and different isotopes will absorb that radiation at different wavelengths, producing a signal that carries the fingerprints of what the air there is made of.
In this case, it was mostly water vapor and carbon monoxide. In the latter, the team managed to distinguish between carbon-12 and carbon-13, marking the first time different isotopes have been measured in the atmosphere of an exoplanet. The researchers were expecting to find carbon-12 dominating, with about one atom in 70 being carbon-13 – but to their surprise, it turns out there’s about twice that amount present.
Exactly how that occurred remains a mystery, but the team has a hypothesis. Within a planetary system, carbon monoxide exists more readily in gaseous form closer to the star, but beyond a certain point it freezes. This point is known as the carbon monoxide snowline, and planets on different sides of it have different isotope ratios. And the planet examined in this study orbits its star at a much greater distance than any known planet in our solar system.
“The planet is more than one hundred and fifty times farther away from its parent star than our Earth is from our Sun,” says Paul Mollière, an author of the study. “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 team says that future isotopic measurements of exoplanets could help us better understand their development and evolution.
The research was published in the journal Nature. The team describes the work in the video below.