Kepler-91b
Giant planet
From Wikipedia, the free encyclopedia
Kepler-91b is a giant planet orbiting Kepler-91, a star slightly more massive than the Sun. Kepler-91 has left the main sequence and is now a red giant branch star.
| Discovery | |
|---|---|
| Discovery date | 2013 |
| Transit (Kepler Mission) | |
| Orbital characteristics | |
| 0.072+0.007 −0.002 AU | |
| 6.24658 d | |
| Inclination | 68.5+1.6 −1 |
| Star | Kepler-91 |
| Physical characteristics | |
| 1.367+0.069 −0.060 RJ | |
| Mass | 0.81+0.18 −0.17 MJ |
Mean density | 0.44 g/cm3 (0.016 lb/cu in) |
| Albedo | 0.39 [1] |
| Temperature | 2132 K |
Discovery and further confirmation
Kepler-91b was detected by analyzing the data of Kepler space telescope where a transit-like signal was found. Initially thought to be a false positive due to light curve variations by a self-luminous object, it was later revealed that due to Kepler-91's low density, its shape is distorted to a slightly ellipsoidal shape due to gravitational effects of the planet. Ellipsoidal light variations caused by Kepler-91b constitute more than the third of the light variations compared to transit depth. Ellipsoidal light variations also allowed to determine the planet's mass. It was also found that Kepler-91b reflects some of the starlight from its star.[2]
Further analysis managed to question the planetary nature of the object, suspecting that it is a self-luminous object.[3] However, the planetary nature was eventually confirmed again through both the radial velocity technique[4] and re-analysis of the light curve modulations.[5]
Characteristics
Kepler-91b is about 14% less massive than Jupiter while being more than 35% larger, making it less than half of the density of water. Kepler-91b orbits around the host star in about 6.25 days. Despite being one of the least edge-on orbits relative to Earth with inclination being about 68.5 degrees, transit was detected due to low semi-major axis to host star radius ratio.
Kepler-91b is expected to be engulfed by the parent star within about 55 million years.[2][1]
Possible trojan companion
The possibility of a trojan planet to Kepler-91b was suggested due to the presence of a small dim in the phase-folded light curve at phase 0.68.[2] This was subsequently studied but the conclusion was that the transit-signal was a false-positive.[6]