Kepler-18
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Kepler-18 is a star with a system of three exoplanets, positioned in the northern Constellation of Cygnus. It has an apparent visual magnitude of 14.0, requiring a telescope to view. Based on parallax measurements, it is located at a distance of approximately 1,430 light-years (440 pc). It is drifting closer with a line of sight velocity component of −18.4 km/s.
This is an older star with an estimated age of around ten billion years. It has similar properties to the Sun with almost the same mass and a 10% larger radius. The star is radiating 93% of the Sun's luminosity from its photosphere at an effective temperature of 5,383 K.
Planetary system
The star is orbited by 3 confirmed transiting planets, announced in 2011. In 2021, it was found the orbital plane of Kepler-18d is slowly changing, likely under the gravitational influence of the additional giant planet.
| Companion (in order from star) | Mass | Semimajor axis (AU) | Orbital period (days) | Eccentricity | Inclination | Radius |
|---|---|---|---|---|---|---|
| b | 6.9 ± 3.4 M🜨 | 0.0447 ± 0.0006 | 3.504725 ± 0.000028 | — | 84.92 ± 0.26° | 2.00 ± 0.10 R🜨 |
| c | 17.3 ± 1.9 M🜨 | 0.0752 ± 0.0011 | 7.6415716 | — | 87.68 ± 0.22° | 5.49 ± 0.26 R🜨 |
| d | 16.4 ± 1.4 M🜨 | 0.1172 ± 0.0017 | 14.858941 | — | 88.07 ± 0.1° | 6.98 ± 0.33 R🜨 |