Ruprecht-Karls-Universität Heidelberg

Heidelberg Astronomers Discover a Very Rare Type of Planet


This artistic image shows Kepler-432b orbiting around his host star. During the "summer season" temperatures on the planets suface will probably reach about 1000 degree centigrade. In reality the planet is much smaller than its red giant star. (Grafics: G. Thimm)

This sketch illustrates the excentric orbit of Kepler-432b in comparison with the more circular path of the planet Mercury around the sun. (Grafics: Sabine Reffert)

Two groups of astronomers from Heidelberg have independently discovered an extremely rare type of planet. Known as Kepler-432b, the celestial body is a close-in massive planet whose days are numbered: its host star will soon have the planet for dinner!

The two teams, one led by Mauricio Ortiz of the Centre for Astronomy of Heidelberg University (ZAH) and the other by Simona Ciceri of the Max Planck Institute for Astronomy (MPIA) in Heidelberg, reported that the planet has a mass six times that of Jupiter, but is about the same size. Kepler-432b orbits what astronomers call a “red giant star”, a star with substantially larger radius than our Sun. As the star is also reddish in colour, astronomers call it a “red giant star”. The shape and the size of the orbit of Kepler-432b are unusual for planets around giant stars. In less than 200 million years the planet will be swallowed up by its host star. The results of this research have been recently published in the “Astronomy & Astrophysics” journal.

“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,” says Dr. Davide Gandolfi from the state observatory Königstuhl, which is part of the Centre for Astronomy. Dr. Gandolfi is a member of the research group that discovered the planet. He explains that the star around which Kepler-432b is orbiting has already exhausted the nuclear fuel in its interior 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 Kepler-432b incredibly close to its host star at some times and much farther away at others, thus creating enormous temperature differences over the course of the planet’s year, which corresponds to 52 Earth days. “During the winter season, the temperature on Kepler-432b is roughly 500 degrees Celsius. In the short summer season, it can increase to nearly 1,000 degrees Celsius,” states astronomer Dr. Sabine Reffert from the state observatory Königstuhl. Kepler-432b was previously identified as a transiting planet candidate by the NASA Kepler satellite mission. From the vantage point of the Earth, a transiting planet passes in front of its host star, periodically dimming the received stellar light. 

Both groups of researchers used the 2.2-metre telescope at Calar Alto Observatory in Andalucía, Spain to collect data. The group from the state observatory also observed Kepler-432b with the 2.6-metre Nordic Optical Telescope on La Palma (Canary Islands, Spain). Thus, they were able to acquire the high-precision measurements needed to determine the planet’s mass. “The discovery of Kepler-432b was possible only thanks to the flexible scheduling of observation time on the telescopes and the outstanding support provided by the staff members at the two sites,” stresses Dr. Gandolfi.

“The days of Kepler-432b are numbered, though,” adds Mauricio Ortiz, a PhD student at Heidelberg University who led one of the two studies of the planet. “In less than 200 million years, Kepler-432b 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”.


Internet information:
NASA Kepler Satellite Mission


Original publications:

  • M. Ortiz, D. Gandolfi, S. Reffert, A. Quirrenbach, H.J. Deeg, R. Karjalainen, P. Montañés-Rodríguez, D. Nespral, G. Nowak, Y. Osorio and E. Palle: Kepler-432 b: a massive warm Jupiter in a 52 day eccentric orbit transiting a giant star, Astronomy & Astrophysics 573 (January 2015), doi: 10.1051/0004-6361/201425146
  • S. Ciceri, J. Lillo-Box, J. Southworth, L. Mancini, T. Henning, D. Barrado: Kepler-432 b: a massive planet in a highly eccentric orbit transiting a red giant, Astronomy & Astrophysics 573 (January 2015), doi: 10.1051/0004-6361/201425145



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