A team of astronomers led by the University of Hawaii Institute for Astronomy has found a massive third exoplanet in the Kepler-88 system located 1243 light-years away in the constellation of Lyra.
The discovery was based on six years of radial velocity (RV) follow-up from the W.M. Keck Observatory High-Resolution Echelle Spectrometer spectrograph. Designated Kepler-88 d, this giant planet, which orbits its host star Kepler-88 (a Sun-type star) in an elliptical orbit lasting 3.8 years, has about 965 Earth-masses. This would make Kepler-88 d approximately 3 times as massive as Jupiter. In case you’re wondering, 10 times Jupiter’s mass is about the theoretical upper limit for a planet.
Two other planets were previously discovered orbiting Kepler-88. Kepler-88 b was discovered using the transit-method in 2012. Being the closest to its host star, it orbits in about 11 days. It is about the diameter of Neptune but only half as dense (~9.5 Earth-masses). Due to extreme transit timing variations (TTVs), astronomers were able to infer the existence of a larger perturbing planet (Kepler-88 c). Through dynamical analysis of the TTVs, they were able to calculate its orbital period and mass. It orbits its host star in about 22 days and has about 214 Earth-masses (~0.67 times Jupiter’s mass). Its existence was confirmed using the RV method in 2013. Unlike Kepler-88 b, however, Kepler-88 c and Kepler-88 d are non-transiting, and thus we cannot deduce their radii.
Jupiter is the undisputed heavyweight in our solar system. As such, its gravitational influence is instrumental in the formation and evolution of the inner planets. Being three times as massive, we can only hypothesize the influence Kepler-88 d has on its planetary system. Further research will hopefully shed light on the relationship between giant planets and their planetary system’s architecture.
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