Carbon-13 on exoplanet TYC 8998-760-1 b showed that it formed at a huge distance from its star - beyond the carbon monoxide snow line.
Carbon-13 has been detected in the atmosphere of the gas giant TYC 8998-760-1 b, located about 310 light years away. The presence of such an isotope indicates that the exoplanet formed at a great distance from the parent star, beyond the boundary of the carbon monoxide snow line. This is reported in a new article published in the journal Nature.
In 2019, astronomers discovered two large planets near the distant solar-type star TYC 8998-760-1: one six times more massive than Jupiter, the other 14 times more massive. This was the rare case when exoplanets were captured directly using a VLT telescope armed with a special "coronagraph". That is why scientists noticed the planets, although they are at a very impressive distance from the star and would hardly have been found using transit and other traditional methods.
Thus, the orbit of TYC 8998-760-1 b is about 160 astronomical units (the average distance from the Earth to the Sun); for comparison, Pluto's orbit is "only" 40 astronomical units. Also TYC 8998-760-1 b is twice the size of Jupiter and reflects enough light from the star to be seen with telescopes. Ignas Snellen of the Leiden Observatory in the Netherlands and his colleagues made new such observations.
Scientists used the SINFONI infrared spectrograph mounted on the VLT telescope and obtained the TYC 8998-760-1 b spectrum with absorption lines that indicate the presence of various substances in its atmosphere. Specifically, the researchers found evidence of carbon-13, a stable but fairly rare isotope that only makes up about one percent of carbon on Earth. On TYC 8998-760-1 b, it is most likely a part of CO molecules, carbon monoxide.
The amount of carbon-13 turned out to be many times higher than astronomers expected. They attribute this to the great distance of the planet from the parent star: beyond the snow line of carbon monoxide - the conditional boundary beyond which the temperature is so low that this volatile compound goes into a solid state. Forming in this region, TYC 8998-760-1 b collected large volumes of CO in the form of ice, and with it carbon-13 isotopes.
The authors note that the planets of the solar system are all much closer to the star, so we apparently do not have exact analogs of TYC 8998-760-1 b. But something similar can be seen in Neptune and Uranus: the shells of these gas giants are rich in deuterium, because they formed behind the snow line of water. According to scientists, in the future, the study of the isotopic composition of exoplanets may become a new tool for determining the place in which they were born.