A massive, dense extrasolar gas giant with extreme seasons has been discovered by two research teams. One was a group led by Simona Ciceri of the Max Planck Institute for Astronomy and one was led by Mauricio Ortiz of the Centre for Astronomy of Heidelberg University.
The astronomers, working independently of each other, say the planet, named Kepler-432b, has six times the mass of Jupiter, but is about the same size.
Also unusual are the shape and the size of its orbit, especially for a planet like Kepler-432b that is revolving around a giant star. In less than 200 million years, this “red giant” will in all likelihood engulf the planet.
Dr. Davide Gandolfi from the state observatory Königstuhl, and a member of the research group that discovered the planet said:
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.
Orbits Red Giant
The star that Kepler-432b orbits has already exhausted the nuclear fuel in its core and is gradually expanding. It has a radius that is already four times our Sun and it will get even bigger in the future. Astronomers call it a Red Giant, since the star is reddish in colour.
It’s unique orbit brings Kepler-432b unbelievably close to its parent star at some times and much farther away at others. This creates colossal temperature differences over the course of the planet’s year, which equals 52 Earth days.
Until now, astronomers have only observed 5 planets, including Kepler-432b, which are so abnormally close to their red giant hosts. Of these, only two, namely Kepler-432b and Kepler-91b have been observed sufficiently closely to determine both their mass and their size.
According to Königstuhl astronomer Dr. Sabine Reffert:
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.
Kepler-432b was identified earlier 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.
Getting High-precision Measurements
Both teams of researchers used the CAFE spectrograph at the 2.2 meter telescope at Calar Alto Observatory in Andalucía, Spain to detect the planet’s traces in the spectrum of the star, with the “radial velocity method”. The group from Königstuhl observatory also observed Kepler-432b with the Nordic Optical Telescope on La Palma, in the Canary Islands.
The two telescopes enabled them to obtain the high-precision measurements needed to determine the planet’s mass.
Adds Heidelberg University’s Mauricio Ortiz, who led one of the two studies of the planet:
The days of Kepler-432b are numbered, though. 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.
Simona Ciceri, of the Max Planck Institute for Astronomy who led the first of the studies of Kepler-432b, says:
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.
Now it is up to the scientists who simulate planetary interaction with giant stars to re-check their simulations and to come up with an answer.
Shown in the Illustration above, is the orbit of Kepler-432b (inner, red) compared to the orbit of Mercury around the Sun (outer, orange).
The red dot in the middle indicates the position of the star around which the planet is orbiting. The size of the star is shown to scale, while the size of the planet has been magnified ten times for illustration purposes.
The orbit of Kepler-432b is highly elongated. As a consequence, the distance between the planet and the star as well as the temperature on the planet change dramatically during a single orbit.
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
Illustration by Dr. Sabine Reffert