It is one of the densest planets ever discovered: it has the same size of Jupiter, but six times its mass. And it is a planet from doom: its parent star, a red giant, between 200 million years will engulf it relentlessly.
A giant planet, extremely rare, the extreme seasons and that day – or rather the years – counted. That’s how the researchers describe Kepler-432B, one of the densest planets discovered so far. Two research groups at the University of Heidelberg (Centre for Astronomy and the Max Planck Institute) worked separately but have come together with this extraordinary discovery. The planet has six times the mass of Jupiter, but more or less the same size (for this is definitely very dense).



But bizarre Kepler-432B has also the elliptical orbit around a red giant that probably between 200 million years it will swallow. “Until a few months ago, we did not know the planets in orbit around giant stars whose semi-major axis is less than 0.5 astronomical units. The existence of this type of planets had been predicted theoretically but had not yet been proven because they have a short life and they are hard to find: they are swallowed up by their star as soon as it evolves and becomes a red giant”, says Davide Gandolfi, one of the authors of the study and researcher at the Center for Astronomy of the University of Heidelberg and researcher Rita Levi Montalcini at the Department of Physics of the University of Turin. “Kepler-432 has a semi-major axis of 0.3 astronomical units and it is the fifth planet discovered so close to a red giant. It will not have a long life: between about 200 million years -a small time, astronomically speaking – will be “swallowed up” by its star! “, he added.



“Most of the known planets around giant stars have orbits large and circular – said then the Italian researcher -. With its small and very elongated orbit, Kepler-432B is a true exception among the planets of this type. “This star has already spent nuclear fuel and for this it is gradually expanding. Its radius is already four times that of our sun and will grow more and more. For this the future of the planet is now marked.
The orbit of Kepler-432B to periapsis comes incredibly close to its star and much farther to apoapsis (The point at which an orbiting object is farthest away from the center of mass of the body it is orbiting), thus creating huge temperature differences during the year of the planet (which corresponds to 52 Earth days). “During the winter, the temperature on Kepler-432B is about 500 degrees Celsius, while in the short summer period, you get up to nearly 1,000 degrees,” said Sabine Reffert. We say that its temperature does not make it certainly a candidate to be included in the list of possible habitable planets discovered by Kepler (has been identified by the method of transit).
Both research groups have used the 2.2-meter telescope at the Calar Alto Observatory in Spain, to collect their data. One of the team also used the Nordic Optical Telescope in the Canary Islands. Thanks to these optical instruments, experts have obtained precise measurements on the mass of Kepler-432B.
Just the fact that Kepler-432B will be destroyed by the red giant ‘could be the reason why you do not often find planets similar. Their life – said Mauricio Ortiz, lead author of one of two studies – is very short, astronomically speaking.”

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