The first finding of isotopes in an exoplanet's atmosphere was made on a world little over 300 light-years away.
Astronomers discovered a type of carbon known as carbon-13 in the haze surrounding the gaseous exoplanet TYC 8998-760-1b. This discovery shows that the exoplanet developed distant from its parent star, beyond a certain snow line, in the icy depths of its system.
Researchers said the discovery provides a new perspective on the poorly understood process of planet formation.
Noteworthy Discovery
The 2019 discovery of TYC 8998-760-1 b was already noteworthy. Science Alert said it belongs to a very small number of exoplanets that we have been able to image directly.
Because stars are so bright, and planets are so dark in comparison, we normally identify them by measuring the gravitation or light dampening effect they have on their host star as they pass in front of it.
These methods work best for planets orbiting their stars near to them. However, TYC 8998-760-1 b orbits its star at a considerable distance — roughly 160 astronomical units. Pluto orbits the Sun at a distance of 40 astronomical units from the Sun.
The exoplanet is likewise a chonk, with a mass and size roughly 14 times that of Jupiter, making it relatively brilliant with reflected starlight. So, led by Zhang, a group of researchers looked closer to see if the light reflected by the star could reveal anything.
Detectives Coming in March
They used the European Southern Observatory's Very Large Telescope in Chile's Spectrograph for Integral Field Observations in the Near Infrared (SINFONI) instrument. The team was hunting for absorption traits using this equipment, which observes a spectrum of light.
When specific wavelengths of light are absorbed by certain elements, black lines appear in a spectrum. The wavelengths absorbed by TYC 8998-760-1 b are compatible with carbon-13, which is largely tied up in carbon monoxide gas, according to the researchers.
Isotopes are a fascinating subject. They are all different types of the same element, with the same number of protons and electrons but different quantities of neutrons.
A Very Special Difference
The most common stable carbon isotope, carbon-12, has six of each. Carbon-13 contains seven neutrons but six protons and six electrons. This is significant since their formation paths differ and they behave differently depending on their surroundings.
The researchers expected a particular amount of carbon on TYC 8998-760-1 b. They discovered twice as much carbon-13 in the exoplanet's atmosphere as they predicted. This, the team believes, can reveal something about the conditions that led to the formation of TYC 8998-760-1 b.
"The planet is more than one hundred and fifty times farther away from its parent star than our Earth is from our Sun," astrophysicist Paul Mollière of the Max Planck Institute for Astronomy in Germany explained in a statement released by 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."
This area would be beyond the carbon monoxide snow line, which is the distance beyond which carbon monoxide condenses and freezes from gas to ice (different gases have different snow lines).
Carbon monoxide ices would be present on any exoplanets forming that far from the star's warmth. The researchers hypothesized that because the known planets in the Solar System are closer to the Sun than this distance, they would not develop with as much carbon monoxide as TYC 8998-760-1 b.
In the Solar System, Neptune and Uranus have more deuterium, a hydrogen isotope with one proton and one neutron (regular hydrogen only has a proton), than Jupiter. Planet formation beyond the water-snow line is thought to be the cause of this.
The discovery of isotopes in atmospheres will not be possible for many exoplanets for some time, but as telescopes improve, it may provide a new way to investigate exoplanet formation, according to the researchers.
Researchers reported their study, titled "The 13co-Rich Atmosphere of a Young Accreting Super-Jupiter," has been published in Nature.
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