Kepler-186
Red dwarf with the first Earth-sized planet in the habitable zone.
Kepler-186 is a red dwarf star in the constellation Cygnus, located 177.5 parsecs away. It is notable for hosting the first Earth-sized planet discovered in the habitable zone, Kepler-186f, along with four other known planets.
Quick Facts
- Distance
- 177.5 parsecs (579 light years)
- Spectral type
- M-type red dwarf
- Mass
- 0.544 times the Sun's mass
- Metallicity
- −0.26 dex (roughly half the Sun's)
- Number of known planets
- 5
- Variable star type
- BY Draconis variable
- Variability period
- 33.695 days
Facts from the source article.
Naming
The star was initially catalogued as KIC 8120608 in the Kepler Input Catalog and later designated KOI 571 as a Kepler Object of Interest. Planetary candidates were detected by the Kepler Mission using the transit method, which observes dips in brightness caused by orbiting planets. The 2MASS survey also recorded the star as 2MASS J19543665+4357180.
Star
In the infrared, the star has H and K band magnitudes of 11.605 and a J band magnitude of 12.473. Its visual magnitudes are 14.90 (R) and 16.40 (B). It is a BY Draconis variable, with brightness changes likely due to starspots, and a variability period of 33.695 days. The star is an M-type red dwarf bordering on K-type, with a mass 0.544 times that of the Sun.
Planetary system
All five known planets are expected to have solid surfaces. The smallest, Kepler-186b, is 8% larger than Earth; the largest, Kepler-186d, is nearly 40% larger. The four innermost planets are probably tidally locked, while Kepler-186f, farther out, may not be tidally locked due to weaker tidal effects; there is a roughly 50-50 chance it is locked. Its day could be weeks or months long. The system's age is poorly constrained but likely greater than a few billion years. Simulations suggest a possible additional non-transiting low-mass planet between Kepler-186e and Kepler-186f. Conjectures based on the Titius–Bode law indicate there could be two small planets between e and f and a larger one beyond f, which would need an orbital radius beyond 16.4 AU for stability. The star's low metallicity is associated with a decreased chance of giant planets but an increased chance of Earth-sized planets.
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