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 possible evidence of an exoplanet was noted in 1917 but was not recognized as such. The first confirmation of detection occurred in 1992. A different planet, init ...

orbiting the

red dwarf ''Red Dwarf'' is a British science fiction comedy franchise created by Rob Grant and Doug Naylor, which primarily consists of a television sitcom that aired on BBC Two between 1988 and 1999, and on Dave since 2009, gaining a cult following. T ...

star

Kepler-186 Kepler-186 is a main-sequence M1-type dwarf star, located 178.5 parsecs (582 light years) away in the constellation of Cygnus. The star is slightly cooler than the sun, with roughly half its metallicity. It is known to have five planets ...

, approximately 582

light years A light-year, alternatively spelled light year, is a large unit of length used to express astronomical distances and is equivalent to about 9.46 trillion kilometers (), or 5.88 trillion miles ().One trillion here is taken to be 1012 ...

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 origins of the e ...

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 occurs 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. A ...

, like

Venus Venus is the second planet from the Sun. It is sometimes called Earth's "sister" or "twin" planet as it is almost as large and has a similar composition. As an interior planet to Earth, Venus (like Mercury) appears in Earth's sky never fa ...

. The exoplanet was found by using the

transit method Any planet is an extremely faint light source compared to its parent star. For example, a star like the Sun is about a billion times as bright as the reflected light from any of the planets orbiting it. In addition to the intrinsic difficulty o ...

, 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 Mercury commonly refers to: * Mercury (planet), the nearest planet to the Sun * Mercury (element), a metallic chemical element with the symbol Hg * Mercury (mythology), a Roman god Mercury or The Mercury may also refer to: Companies * Merc ...

). 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 body, 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 ...

, 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 refers to 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 e ...

, 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 orbi ...

(obliquity) is likely very small, in which case it would not have tilt-induced seasons as Earth and Mars do. Its orbit is probably close to circular, so it will also lack eccentricity-induced seasonal changes like those of

Mars Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, only being larger than Mercury (planet), Mercury. In the English language, Mars is named for the Mars (mythology), Roman god of war. Mars is a terr ...

. 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 disused 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 orbit ...

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 ''Kepler''. Overview The Kepler SCP targets were observed by the 2MASS project ...

(KIC), and then progressed as a candidate host of planets to a Kepler Object of Interest (KOI). Thus, Kepler 186 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)