Kepler-91b is a giant planet orbiting
Kepler-91, a star slightly more massive than the
Sun
The Sun is the star at the center of the Solar System. It is a nearly perfect ball of hot plasma, heated to incandescence by nuclear fusion reactions in its core. The Sun radiates this energy mainly as light, ultraviolet, and infrared radi ...
. Kepler-91 has left the main sequence and is now a
red giant branch
The red-giant branch (RGB), sometimes called the first giant branch, is the portion of the giant branch before helium ignition occurs in the course of stellar evolution. It is a stage that follows the main sequence for low- to intermediate-mass sta ...
star.
Discovery and further confirmation
Kepler-91b was detected by analyzing the data of
Kepler spacecraft
The Kepler space telescope is a disused space telescope launched by NASA in 2009 to discover Earth-sized planets orbiting other stars. Named after astronomer Johannes Kepler, the spacecraft was launched into an Earth-trailing heliocentric orb ...
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 low density of Kepler-91's shape is distorted to slightly ellipsoidal shape due to gravitational effects of the planet. Ellipsoidal light variations caused by Kepler-91b constitute more than the third of 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.
Further analysis managed to question the planetary nature of the object, suspecting that it is a self-luminous object.
However, the planetary nature was eventually confirmed again through both the radial velocity technique and re-analysis of the light curve modulations.
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.
Possible trojan companion
The possibility of a
trojan planet
In astronomy, a co-orbital configuration is a configuration of two or more astronomical objects (such as asteroids, moons, or planets) orbiting at the same, or very similar, distance from their primary, i.e. they are in a 1:1 mean-motion resonan ...
to Kepler-91b was suggested due to the presence of a small dim in the phase-folded light curve at phase 0.68.
This was subsequently studied but the conclusion was that the transit-signal was a false-positive.
References
External links
Technology.org: Kepler-91b: a planet at the end of its life
{{2013 in space
Exoplanets discovered in 2013
Transiting exoplanets
Exoplanets discovered by the Kepler space telescope
Lyra (constellation)
Hot Jupiters