Using data from NASA’s Kepler mission, two teams of astronomers, led by Mauricio Ortiz from the University of Heidelberg and Simona Ciceri of the Max Planck Institute for Astronomy, have independently discovered a new extrasolar gas giant that is almost six times more massive than Jupiter, but about the same size.

The newly discovered alien world, named Kepler-432b, is approximately 2,850 light-years away. It is one of the most dense and massive planets known so far.

The planet has a mass 5.84 times that of Jupiter and orbits its parent star, the red giant Kepler-432, in 52 Earth days.

The shape and the size of its orbit are unusual for a planet like Kepler-432b that is revolving around a giant star.

“The majority of known planets moving around giant stars have large and circular orbits. With its small and highly elongated orbit, Kepler-432b is a real ‘maverick’ among planets of this type,” said Dr Davide Gandolfi from the University of Heidelberg in Germany, who is a member of Mauricio Ortiz’s team.

“The host star, Kepler-432, has already exhausted the nuclear fuel in its core and is gradually expanding. Its radius is already four times that of our Sun and it will get even larger in the future.”

The orbit brings the planet incredibly close to Kepler-432 at some times and much farther away at others, thus creating enormous temperature differences over the course of the planet’s year.

“During the winter season, the temperature on Kepler-432b is roughly 500 degrees Celsius,” said Dr Sabine Reffert, also from the University of Heidelberg.

“In the short summer season, it can increase to nearly 1,000 degrees Celsius.”

Mauricio Ortiz added: “the days of Kepler-432b are numbered, though. In less than 200 million years, the planet will be swallowed by its continually expanding host star.”

“This might be the reason why we do not find other planets like Kepler-432b – astronomically speaking, their lives are extremely short.”

Until now, astronomers have discovered only five exoplanets, including Kepler-432b, which are unusually close to their red giant hosts.

Of these, only two – Kepler-432b and Kepler-91b – have been observed sufficiently closely to determine both their mass and their size. Another two have been detected only by measuring their planetary transits, while one has been found using spectral measurements only.

If a phenomenon is fairly short-lived, astronomers do not expect to observe many examples of it.

“At this point, there are two possibilities: either we have been unusually lucky to observe two rare, close planetary orbits such as those of Kepler-432b and Kepler-91b. Or else, planets like these survive for much longer than was previously assumed,” Simona Ciceri said.

The discovery of Kepler-432b is described in two papers published in the journal Astronomy & Astrophysics (paper 1 & paper 2).

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Mauricio Ortiz et al. 2015. Kepler-432 b: a massive warm Jupiter in a 52-day eccentric orbit transiting a giant star. A&A 573, L6; doi: 10.1051/0004-6361/201425146

S. Ciceri et al. 2015. Kepler-432 b: a massive planet in a highly eccentric orbit transiting a red giant. A&A 573, L5; doi: 10.1051/0004-6361/201425145