Exoplanet

extrasolar planetexoplanetsplanetextrasolar planetsplanetsextra-solar planetsextrasolarextra-solar planetother planetsexoplanetary systems
An exoplanet or extrasolar planet is a planet outside the Solar System.wikipedia
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List of multiplanetary systems

List of planetary systemsList of stars with extrasolar planetsmultiple planetary systems
In several cases, multiple planets have been observed around a star.
From the total of stars known to have exoplanets (as of ), there are a total of known multiplanetary systems, or stars with at least two confirmed planets, beyond the Solar System.

List of exoplanet extremes

least massive planetList of extrasolar planet extremeslowest metallicity planet-bearing star
The least massive planet known is Draugr (also known as PSR B1257+12 A or PSR B1257+12 b), which is about twice the mass of the Moon. The most massive planet listed on the NASA Exoplanet Archive is HR 2562 b, about 30 times the mass of Jupiter, although according to some definitions of a planet (based on the nuclear fusion of deuterium ), it is too massive to be a planet and may be a brown dwarf instead.
The following are lists of extremes among the known exoplanets.

PSR B1257+12 A

DraugrPSR B1257+12 bA
The least massive planet known is Draugr (also known as PSR B1257+12 A or PSR B1257+12 b), which is about twice the mass of the Moon.
PSR B1257+12 b, alternatively designated PSR B1257+12 A, also named Draugr, is an extrasolar planet approximately 2,300 light-years away in the constellation of Virgo.

NASA Exoplanet Archive

The NASA Exoplanet ArchiveExoplanet Archive
The most massive planet listed on the NASA Exoplanet Archive is HR 2562 b, about 30 times the mass of Jupiter, although according to some definitions of a planet (based on the nuclear fusion of deuterium ), it is too massive to be a planet and may be a brown dwarf instead.
The NASA Exoplanet Archive is an online astronomical exoplanet catalog and data service that collects and serves public data that support the search for and characterization of extra-solar planets (exoplanets) and their host stars.

Circumstellar habitable zone

habitable zonehabitable zonesGoldilocks zone
About 1 in 5 Sun-like stars have an "Earth-sized" planet in the habitable zone.
Most such planets, being either super-Earths or gas giants, are more massive than Earth, because such planets are easier to detect.

List of nearest exoplanets

the closest known exoplanetnearest exoplanet
The nearest exoplanet is Proxima Centauri b, located 4.2 light-years (1.3 parsecs) from Earth and orbiting Proxima Centauri, the closest star to the Sun.
There are known exoplanets, or planets outside our solar system that orbit a star, as of ; only a small fraction of these are located in the vicinity of the Solar System.

Proxima Centauri b

Proxima bbPale Red Dot
The nearest exoplanet is Proxima Centauri b, located 4.2 light-years (1.3 parsecs) from Earth and orbiting Proxima Centauri, the closest star to the Sun.
Proxima Centauri b (also called Proxima b or Alpha Centauri Cb) is an exoplanet orbiting in the habitable zone of the red dwarf star Proxima Centauri, which is the closest star to the Sun and part of a triple star system.

Extragalactic planet

extragalactic exoplanetextragalactic originRogue extragalactic planets
Nonetheless, evidence suggests that extragalactic planets, exoplanets farther away in galaxies beyond the local Milky Way galaxy, may exist.
An extragalactic planet, also known as an extragalactic exoplanet, is a star-bound planet, or rogue planet, located outside of the Milky Way Galaxy.

Discoveries of exoplanets

Discoveries of extrasolar planetsexoplanet discoveryfirst suspected scientific detection
The first suspected scientific detection of an exoplanet occurred in 1988.
An exoplanet (extrasolar planet) is a planet located outside the Solar System.

Extraterrestrial life

alienextraterrestrialaliens
The discovery of exoplanets has intensified interest in the search for extraterrestrial life.
Nonetheless, on 4 November 2013, astronomers reported, based on Kepler space mission data, that there could be as many as 40 billion Earth-sized planets orbiting in the habitable zones of Sun-like stars and red dwarfs in the Milky Way, 11 billion of which may be orbiting Sun-like stars.

Jupiter

JovianGioveplanet Jupiter
The most massive planet listed on the NASA Exoplanet Archive is HR 2562 b, about 30 times the mass of Jupiter, although according to some definitions of a planet (based on the nuclear fusion of deuterium ), it is too massive to be a planet and may be a brown dwarf instead.
A "Jupiter mass" ( or ) is often used as a unit to describe masses of other objects, particularly extrasolar planets and brown dwarfs.

Planetary habitability

habitabilityhabitablehabitable planet
The study of planetary habitability also considers a wide range of other factors in determining the suitability of a planet for hosting life.
The discovery of extrasolar planets, beginning in the early 1990s and accelerating thereafter, has provided further information for the study of possible extraterrestrial life.

Pulsar

pulsarsradio pulsarRotation-powered pulsar
Shortly afterwards, the first confirmation of detection came in 1992, with the discovery of several terrestrial-mass planets orbiting the pulsar PSR B1257+12. On 9 January 1992, radio astronomers Aleksander Wolszczan and Dale Frail announced the discovery of two planets orbiting the pulsar PSR 1257+12.
The first extrasolar planets were discovered around a pulsar, PSR B1257+12.

Giordano Bruno

BrunoBruno, GiordanoBruno's cosmology
In the sixteenth century, the Italian philosopher Giordano Bruno, an early supporter of the Copernican theory that Earth and other planets orbit the Sun (heliocentrism), put forward the view that the fixed stars are similar to the Sun and are likewise accompanied by planets.
He proposed that the stars were distant suns surrounded by their own planets, and he raised the possibility that these planets might foster life of their own, a philosophical position known as cosmic pluralism.

51 Pegasi

51 Peg51 Peg (Helvetios)a star
The first confirmation of an exoplanet orbiting a main-sequence star was made in 1995, when a giant planet was found in a four-day orbit around the nearby star 51 Pegasi.
It was the first main-sequence star found to have an exoplanet (designated 51 Pegasi b, officially named Dimidium, formerly unofficially dubbed Bellerophon) orbiting it.

Hot Jupiter

hot JupitersPuffy planetultra-short period planet
In 1952, more than 40 years before the first hot Jupiter was discovered, Otto Struve wrote that there is no compelling reason why planets could not be much closer to their parent star than is the case in the Solar System, and proposed that Doppler spectroscopy and the transit method could detect super-Jupiters in short orbits.
Hot Jupiters are a class of gas giant exoplanets that are inferred to be physically similar to Jupiter but that have very short orbital periods (P

Transit (astronomy)

transittransitingtransits
Transit photometry and Doppler spectroscopy have found the most, but these methods suffer from a clear observational bias favoring the detection of planets near the star; thus, 85% of the exoplanets detected are inside the tidal locking zone.
The transit method can be used to discover exoplanets.

PSR B1257+12

PSR 1257+12PSR B1257+12 DLich (pulsar)
Shortly afterwards, the first confirmation of detection came in 1992, with the discovery of several terrestrial-mass planets orbiting the pulsar PSR B1257+12. On 9 January 1992, radio astronomers Aleksander Wolszczan and Dale Frail announced the discovery of two planets orbiting the pulsar PSR 1257+12.
They were both the first extrasolar planets and the first pulsar planets to be discovered; B and C in 1992 and A in 1994.

William Stephen Jacob

In 1855 William Stephen Jacob at the East India Company's Madras Observatory reported that orbital anomalies made it "highly probable" that there was a "planetary body" in this system.
His early claim of 1855 to have detected an exoplanet, in orbit around 70 Ophiuchi, is now thought to have been mistaken.

Gravitational microlensing

microlensingmicrolensing eventdetected by microlensing
In February 2018, researchers using the Chandra X-ray Observatory, combined with a planet detection technique called microlensing, found evidence of planets in a distant galaxy, stating "Some of these exoplanets are as (relatively) small as the moon, while others are as massive as Jupiter. Unlike Earth, most of the exoplanets are not tightly bound to stars, so they're actually wandering through space or loosely orbiting between stars. We can estimate that the number of planets in this [faraway] galaxy is more than a trillion.
Since then, microlensing has been used to constrain the nature of the dark matter, detect exoplanets, study limb darkening in distant stars, constrain the binary star population, and constrain the structure of the Milky Way's disk.

Methods of detecting exoplanets

transit methodTransitdirect imaging
In 1952, more than 40 years before the first hot Jupiter was discovered, Otto Struve wrote that there is no compelling reason why planets could not be much closer to their parent star than is the case in the Solar System, and proposed that Doppler spectroscopy and the transit method could detect super-Jupiters in short orbits. There are many methods of detecting exoplanets. In 1991 Andrew Lyne, M. Bailes and S. L. Shemar claimed to have discovered a pulsar planet in orbit around PSR 1829-10, using pulsar timing variations.
For those reasons, very few of the exoplanets reported have been observed directly, with even fewer being resolved from their host star.

Orbital period

periodsynodic periodsynodic
In the 1890s, Thomas J. J. See of the University of Chicago and the United States Naval Observatory stated that the orbital anomalies proved the existence of a dark body in the 70 Ophiuchi system with a 36-year period around one of the stars.
The orbital period is the time a given astronomical object takes to complete one orbit around another object, and applies in astronomy usually to planets or asteroids orbiting the Sun, moons orbiting planets, exoplanets orbiting other stars, or binary stars.

Aleksander Wolszczan

Alex Wolszczan
On 9 January 1992, radio astronomers Aleksander Wolszczan and Dale Frail announced the discovery of two planets orbiting the pulsar PSR 1257+12.
He is the co-discoverer of the first extrasolar planets and pulsar planets.

Pulsar planet

pulsar planetsplanet
In 1991 Andrew Lyne, M. Bailes and S. L. Shemar claimed to have discovered a pulsar planet in orbit around PSR 1829-10, using pulsar timing variations.
The first such planet to be discovered was around a millisecond pulsar and was the first extrasolar planet to be confirmed as discovered.

Red dwarf

M dwarfredred dwarf stars
Assuming there are 200 billion stars in the Milky Way, it can be hypothesized that there are 11 billion potentially habitable Earth-sized planets in the Milky Way, rising to 40 billion if planets orbiting the numerous red dwarfs are included.
Many red dwarfs are orbited by exoplanets, but large Jupiter-sized planets are comparatively rare.