Kepler-91b

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.

Kepler-91b
Discovery
Discovery date2013
Transit (Kepler Mission)
Orbital characteristics
0.072+0.007
−0.002 AU
6.24658 d
Inclination68.5+1.6
−1
StarKepler-91
Physical characteristics
Mean radius
1.322+0.094
−0.086 RJ
Mass0.88+0.33
−0.17 MJ
Mean density
0.44 g/cm3 (0.016 lb/cu in)
Albedo0.39 [1]
Temperature2132 K

    Discovery and further confirmation

    Kepler-91b was detected by analyzing the data of Kepler spacecraft 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.[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]

    gollark: Idea: be really inconsistent about what stuff *actually* costs a lot to make/is important/valuable, to trick people into damaging and stealing random useless stuff!
    gollark: Well, the forcefield should get him anyway.
    gollark: Uprisings will be removed with laser bees.
    gollark: The laser bees sting any hostile mob which spawns, so they don't exist.
    gollark: We also used quarries to unexist most nearby ore, and also all caves underneath the test village are lit up now, and also also there are no hostile mobs there.

    References
    1. Esteves, Lisa J.; De Mooij, Ernst J. W.; Jayawardhana, Ray (2014). "Changing Phases of Alien Worlds: Probing Atmospheres of Kepler Planets with High-Precision Photometry". The Astrophysical Journal. 804 (2): 150. arXiv:1407.2245. Bibcode:2015ApJ...804..150E. doi:10.1088/0004-637X/804/2/150.
    2. Lillo-Box, J.; Barrado, D.; Moya, A.; Montesinos, B.; Montalbán, J.; Bayo, A.; Barbieri, M.; Régulo, C.; Mancini, L.; Bouy, H.; Henning, T. (2013). "Kepler-91b: A planet at the end of its life. Planet and giant host star properties via light-curve variations". Astronomy & Astrophysics. 562: A109. arXiv:1312.3943. Bibcode:2014A&A...562A.109L. doi:10.1051/0004-6361/201322001.
    3. Sliski, David H.; Kipping, David M. (2014). "A High False Positive Rate for Kepler Planetary Candidates of Giant Stars using Asterodensity Profiling". The Astrophysical Journal. 788 (2): 148. arXiv:1401.1207. Bibcode:2014ApJ...788..148S. doi:10.1088/0004-637X/788/2/148.
    4. Lillo-Box, J.; Barrado, D.; Henning, Th.; Mancini, L.; Ciceri, S.; Figueira, P.; Santos, N. C.; Aceituno, J.; Sánchez, S. (August 2014). "Radial velocity confirmation of Kepler-91 b". Astronomy & Astrophysics. 568: L1. arXiv:1408.1528. doi:10.1051/0004-6361/201424587. ISSN 0004-6361.
    5. Barclay, Thomas; Endl, Michael; Huber, Daniel; Foreman-Mackey, Daniel; Cochran, William D.; MacQueen, Phillip J.; Rowe, Jason F.; Quintana, Elisa V. (2015). "Radial Velocity Observations and Light Curve Noise Modeling Confirm that Kepler-91b is a Giant Planet Orbiting a Giant Star". The Astrophysical Journal. 800 (1): 46. arXiv:1408.3149. doi:10.1088/0004-637X/800/1/46. ISSN 0004-637X.
    6. Placek, Ben; Knuth, Kevin H.; Angerhausen, Daniel; Jenkins, Jon M. (2015). "Characterization of Kepler-91b and the Investigation of a Potential Trojan Companion Using EXONEST". The Astrophysical Journal. 814 (2): 147. arXiv:1511.01068. Bibcode:2015ApJ...814..147P. doi:10.1088/0004-637X/814/2/147.
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