Kepler-289
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Kepler-289 (PH3) is a rotating variable star slightly more massive than the Sun, with a spectral type of G2, 2370 light-years away from Earth in the constellation of Cygnus. It hosts a system of multiple exoplanets.
Planetary system
Kepler-289 hosts three transiting planets, discovered using the Kepler space telescope. Two planets, Kepler-289b and Kepler-289c, were confirmed in 2014 as part of a study using statistical validation to confirm hundreds of Kepler candidates. A third planet, Kepler-289d, was found by the Planet Hunters citizen science project, hence the other designation for the system, PH3.
Different sources present conflicting models of Kepler-289's planetary system. The discovery paper for planet d says that it has an orbital period of 66 days, and that a 330-day candidate is an alias of the true period of planet d. A 2023 follow-up study also reports a 66-day period for planet d. However, a 2025 study reports a 330-day planet, and says that the 66-day signal "is no longer believed to exist in the data". The NASA Exoplanet Archive lists both a 66-day and a 330-day planet, the latter called Kepler-289e, but no literature source claims the existence of more than three planets in the system.
| Companion (in order from star) | Mass | Semimajor axis (AU) | Orbital period (days) | Eccentricity | Inclination | Radius |
|---|---|---|---|---|---|---|
| b | 3.70+3.79 −1.96 M🜨 | 0.21±0.01 | 34.5383±0.0006 | — | 88.98+0.06 −0.07° | 2.49±0.07 R🜨 |
| d | 5.33+0.43 −0.42 M🜨 | 0.33±0.02 | 66.0282+0.0044 −0.0039 | — | 89.31±0.04° | 3.03±0.08 R🜨 |
| c | 0.49±0.02 MJ | 0.51±0.03 | 125.8723+0.0035 −0.0021 | — | 89.78±0.04° | 1.002±0.019 RJ |