| Discovery | |
|---|---|
| Discovery site | Kepler Space Observatory |
| Discovery date | 17 April 2014 |
| Transit | |
| Orbital characteristics | |
| 0.11–0.1216AU | |
| Eccentricity | <0.24 |
| 22.407704d | |
| Inclination | 88.24 |
| Star | Kepler-186 |
| Physical characteristics | |
| 1.27±0.15R🜨 | |
| Mass | ~2.29ME |
| Temperature | Teq: 323 K (50 °C; 122 °F) |
Kepler-186e (also known by its Kepler Object of Interest designationKOI-571.04) is a confirmedexoplanet orbiting thered dwarf starKepler-186, approximately 582light years away from Earth in theconstellation ofCygnus. It is near the optimistic habitable zone but probably not in it, possibly making it have arunaway greenhouse effect, likeVenus. The exoplanet was found by using thetransit method, in which the dimming effect that a planet causes as it crosses in front of its star is measured. Four additional planets orbiting the star (all modestly larger than Earth) were also discovered.
The exoplanet is only slightly larger than Earth, with a radius 1.27–1.33 times that of Earth. Its mass is not known but it is likely to have a similar composition to Earth, giving it a mass of about 2.29–2.72 times the mass of the Earth. Kepler-186e orbits an M-dwarf star with about 4% of the Sun's luminosity with an orbital period of 22.4077 days and an orbital radius of about 0.11 times that of Earth's (compared to 0.39AU forMercury). The habitable zone for this system is estimated conservatively to extend over distances receiving from 88% to 25% of Earth's illumination (from 0.22 to 0.40 AU).[1]
The star hosts four other planets discovered so far. Because of the very slow evolution of red dwarfs, the age of the Kepler-186 system is poorly constrained, although it is likely to be greater than a few billion years.[3] Due to its proximity to its star, Kepler-186e is probablytidally locked, facing one side to its star at all times, and one side facing away from its star at all times. The side in permanent daylight would be extremely hot and the side in permanent darkness would be extremely cold. But between these hostile environments, there would be a sliver ofhabitability, which could support life.
Kepler-186e'saxial tilt (obliquity) is likely very small. Its orbit is probably close to circular, so it will lack seasonal changes. However, the axial tilt could be larger (about 23 degrees) if another undetected nontransiting planet orbits between it and Kepler-186f; planetary formation simulations have shown that the presence of at least one additional planet in this region is likely. If such a planet exists, it cannot be much more massive than Earth as it would then cause orbital instabilities.[3]
The exoplanet, along with the other planets of the Kepler-186 system (including 186f), were announced on April 17, 2014, in an article published by NASA.[2]
As theKepler telescope observational campaign proceeded, an initially identified system was entered in theKepler Input Catalog (KIC), and then progressed as a candidate host of planets to aKepler Object of Interest (KOI). Thus,Kepler-186 started asKIC 8120608 and then was identified asKOI 571.[4] Kepler-186e was mentioned when known as KOI-571-04 or KOI-571.04 or using similar nomenclatures in 2013 in various discussions and publications before its full confirmation.[5]
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