Kepler-186e (also known by its Kepler Object of Interest designation ''KOI-571.04'') is a confirmed

exoplanet An exoplanet or extrasolar planet is a planet outside the Solar System. The first confirmed detection of an exoplanet was in 1992 around a pulsar, and the first detection around a main-sequence star was in 1995. A different planet, first det ...

orbiting the

red dwarf A red dwarf is the smallest kind of star on the main sequence. Red dwarfs are by far the most common type of fusing star in the Milky Way, at least in the neighborhood of the Sun. However, due to their low luminosity, individual red dwarfs are ...

star

Kepler-186 Kepler-186 is a main-sequence Spectral class#Class M, M1-type Red dwarf, dwarf star, located 177.5 parsecs (579 light years) away in the constellation of Cygnus (constellation), Cygnus. The star is slightly cooler than the sun, with rough ...

, approximately 582

light years A light-year, alternatively spelled light year (ly or lyr), is a unit of length used to express astronomical distances and is equal to exactly , which is approximately 9.46 trillion km or 5.88 trillion mi. As defined by the International Astro ...

away from Earth in the

constellation A constellation is an area on the celestial sphere in which a group of visible stars forms Asterism (astronomy), a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object. The first constellati ...

of Cygnus. It is near the optimistic habitable zone but probably not in it, possibly making it have a

runaway greenhouse effect A runaway greenhouse effect will occur when a planet's atmosphere contains greenhouse gas in an amount sufficient to block thermal radiation from leaving the planet, preventing the planet from cooling and from having liquid water on its surface. ...

, like

Venus Venus is the second planet from the Sun. It is often called Earth's "twin" or "sister" planet for having almost the same size and mass, and the closest orbit to Earth's. While both are rocky planets, Venus has an atmosphere much thicker ...

. The exoplanet was found by using the

transit method Methods of detecting exoplanets usually rely on indirect strategies – that is, they do not directly image the planet but deduce its existence from another signal. Any planet is an extremely faint light source compared to its parent star. For e ...

, 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.

Physical characteristics

Mass, orbit, and composition

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 0.39 AU for Mercury). 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).

Formation, tidal evolution and habitability

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. Due to its proximity to its star, Kepler-186e is probably

tidally locked Tidal locking between a pair of co-orbiting astronomical bodies occurs when one of the objects reaches a state where there is no longer any net change in its rotation rate over the course of a complete orbit. In the case where a tidally 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 of

habitability Habitability is the adequacy of an environment for human living. Where housing is concerned, there are generally local ordinances which define habitability. If a residence complies with those laws, it is said to be habitable. In extreme environ ...

, which could support life. Kepler-186e's

axial tilt In astronomy, axial tilt, also known as obliquity, is the angle between an object's rotational axis and its orbital axis, which is the line perpendicular to its orbital plane; equivalently, it is the angle between its equatorial plane and orbita ...

(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.

Discovery

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.

Previous names

As the

Kepler telescope The Kepler space telescope is a defunct space telescope launched by NASA in 2009 to discover Earth-sized planets orbiting other stars. Named after astronomer Johannes Kepler, the spacecraft was launched into an Earth-trailing heliocentric orb ...

observational campaign proceeded, an initially identified system was entered in the

Kepler Input Catalog The Kepler Input Catalog (or KIC) is a publicly searchable database of roughly 13.2 million targets used for the Kepler Spectral Classification Program (SCP) and the Kepler space telescope. Overview The Kepler SCP targets were observed by t ...

(KIC), and then progressed as a candidate host of planets to a Kepler Object of Interest (KOI). Thus,

started as ''KIC 8120608'' and then was identified as ''KOI 571''. 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. See comment by "Holger 16 November 2013 at 14:21".
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References

Notes

External links

NASA – Kepler Mission

NASA – Kepler Discoveries – Summary Table

Habitable Exolanets Catalog
at UPR-Arecibo. {{Portal bar, Astronomy, Biology 186f Exoplanets discovered in 2014 Kepler-186 Transiting exoplanets Cygnus (constellation)