An international team of astronomers, including scientists from the Max
Planck Institute for Astronomy, have become the first in the world to detect
isotopes in the atmosphere of an exoplanet. It concerns different forms of
carbon in the gaseous giant planet TYC 8998-760-1 b at a distance of 300
light-years in the constellation Musca (Fly). 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. The astronomers hypothesize that
this is because the planet formed at a great distance from its parent star.
The research will appear in the scientific journal Nature.
Isotopes are different forms of the same atom but with a varying number of
neutrons in the nucleus. For example, carbon with six protons typically has
six neutrons (carbon-12), but occasionally seven (carbon-13) or eight
(carbon-14). This property does not change much the chemical properties of
carbon. Still, isotopes form in different ways and often react slightly
differently to the prevailing conditions. Isotopes, therefore, provide
applications in a wide range of research fields: from detecting
cardiovascular disease or cancer to studying climate change and determining
the age of fossils and rocks.
Astronomers from several countries, among them Paul Mollière from the Max
Planck Institute for Astronomy (MPIA) in Heidelberg, Germany, discovered an
unusual ratio between those isotopes in the atmosphere of the young giant
planet TYC 8998-760-1 b. Carbon is present primarily in the form of CO
(carbon monoxide) gas. The planet itself exhibits a mass of about 14 Jupiter
masses and has almost twice the size of Jupiter. Therefore, astronomers
classify it as a super-Jupiter.
The group of scientists, led by first author Yapeng Zhang, a PhD student at
Leiden Observatory, The Netherlands, successfully distinguished 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,” says Zhang. The astronomers had
expected to detect about one in 70 carbon atoms to be carbon-13, but it
seems to be twice as much for this planet. The idea is that the higher
abundance of carbon-13 is somehow related to the formation of the exoplanet.
Mollière explains: “The planet is more than one hundred and fifty times
farther away from its parent star than our Earth is from our Sun. 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.” Suppose
the enrichment in carbon-13 is connected to the freeze-out of CO in the
planet-forming protoplanetary disks. In that case, this could mean that
Solar System planets did not collect much carbon-13-rich ice. A reason may
be that in the Solar System, the distance beyond which CO begins to freeze
out of the gas phase, known as the CO snowline, lies beyond Neptune’s orbit.
Therefore, CO ices have likely rarely been incorporated into the Solar
System planets, leading to a higher isotope ratio. Mollière wrote the data
analysis software and contributed to interpreting the results.
The exoplanet itself, TYC 8998-760-1 b, was discovered only two years ago by
Leiden PhD student Alexander Bohn, co-author of the article. He adds: “It’s
awesome that this discovery has been made close to ‘my’ planet. It will
probably be the first of many.”
Ignas Snellen, professor in Leiden and the driving force behind this subject
for many years, is above all proud. “The expectation is that in the future,
isotopes will further help to understand exactly how, where and when planets
form. This result is just the beginning.”
Reference:
The 13CO-rich atmosphere of a young accreting super-Jupiter by Yapeng
Zhang, Ignas A. G. Snellen, Alexander J. Bohn, Paul Mollière, Christian
Ginski, H. Jens Hoeijmakers, Matthew A. Kenworthy, Eric E. Mamajek, Tiffany
Meshkat, Maddalena Reggiani and Frans Snik, 14 July 2021, Nature. DOI:
10.1038/s41586-021-03616-x
Tags:
Space & Astrophysics