Editing Exoplanet (section)

== History of detection ==
[[File:Exoplanet-Missions-graphic-final-Dec2022.png|thumb|upright=1.3|NASA graphic of present and future exoplanet missions as of 2022.]]

For centuries scientists, philosophers, and science fiction writers suspected that extrasolar planets existed, but there was no way of knowing whether they were real in fact, how common they were, or how similar they might be to the planets of the [[Solar System]]. Various detection claims made in the nineteenth century were rejected by astronomers.

The first evidence of a possible exoplanet, orbiting [[Van Maanen 2]], was recorded in 1917, but was not recognized as such until 2016.<ref>{{Cite journal |last=Farihi |first=J. |date=2016-04-01 |title=Circumstellar debris and pollution at white dwarf stars |url=https://linkinghub.elsevier.com/retrieve/pii/S1387647315300075 |journal=New Astronomy Reviews |volume=71 |pages=9–34 |doi=10.1016/j.newar.2016.03.001 |issn=1387-6473 |arxiv=1604.03092|bibcode=2016NewAR..71....9F }}</ref> The astronomer [[Walter Sydney Adams]] produced a spectrum of the star using [[Mount Wilson Observatory#60-inch telescope|Mount Wilson's 60-inch telescope]] which he interpreted the spectrum to be of an [[F-type main-sequence star]]. This spectrum was reexamined during studies of [[white dwarf]] stars with unpredicted compositions. It is now thought that such a spectrum could be caused by the residue of a nearby exoplanet that had been pulverized by the gravity of the star, the resulting dust then falling onto the star.<ref name="NASA-20171101">{{cite web |last=Landau |first=Elizabeth |title=Overlooked Treasure: The First Evidence of Exoplanets |url=https://exoplanets.nasa.gov/news/1467/overlooked-treasure-the-first-evidence-of-exoplanets |date=1 November 2017 |work=[[NASA]] |access-date=1 November 2017 }}</ref>

Numerous other claims of discovery took place in the mid 20th century, involving 61 Cygnus, Lalande 21185, and Barnard's Star, which weren't discredited until the mid to late 1970s (see Discredited claims below). Another [[Discoveries of exoplanets#1988.E2.80.931994|suspected scientific detection]] of an exoplanet occurred in 1988. Shortly afterwards, the first detection<ref>Encyclopedia of the Solar System, third edition, 2014, page 963, Tilman Spohn, Doris Breuer, Torrence Johnson</ref> that is currently accepted came in 1992 when [[Aleksander Wolszczan]] announced the discovery of two terrestrial-mass planets orbiting the [[millisecond pulsar]] [[PSR B1257+12]].<ref name="Wolszczan" /> 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]]. Some exoplanets have been [[Direct imaging|imaged directly]] by telescopes, but the vast majority have been detected through indirect methods, such as the [[transit method]] and the [[Doppler spectroscopy|radial-velocity method]]. 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."<ref>{{cite magazine |last=Zachos |first=Elaina |title=More Than a Trillion Planets Could Exist Beyond Our Galaxy – A new study gives the first evidence that exoplanets exist beyond the Milky Way. |url=https://www.nationalgeographic.com/science/article/exoplanets-discovery-milky-way-galaxy-spd |archive-url=https://web.archive.org/web/20210428194238/https://www.nationalgeographic.com/science/article/exoplanets-discovery-milky-way-galaxy-spd |url-status=dead |archive-date=28 April 2021 |magazine=[[National Geographic Society]] |date=5 February 2018 |access-date=31 July 2022}}</ref>

=== Early speculations ===
{{More citations needed section|date=October 2024|reason=Claims of historical precidence should include secondary references, not just dates of publication.}}
{{Rquote |right |This space we declare to be infinite... In it are an infinity of worlds of the same kind as our own.|Giordano Bruno (1584)<ref>{{cite book |title=To Infinity and Beyond: A Cultural History of the Infinite |author=Eli Maor |chapter=Chapter 24: The New Cosmology |date=1987 |isbn=978-1-4612-5396-9 |publisher=Birkhäuser |location=Boston, MA |page=[https://archive.org/details/toinfinitybeyond0000maor/page/198 198] |chapter-url=https://books.google.com/books?id=v0btBwAAQBAJ&pg=PA198 |others=Originally in ''De l'infinito universo et mondi'' [''On the Infinite Universe and Worlds''] by Giordano Bruno (1584). |url=https://archive.org/details/toinfinitybeyond0000maor/page/198 }}</ref>}}

In the sixteenth century, the Italian philosopher [[Giordano Bruno]], an early supporter of the [[Nicolaus Copernicus|Copernican]] theory that Earth and other planets orbit the Sun ([[heliocentrism]]), put forward the view that fixed stars are similar to the Sun and are likewise accompanied by planets.

In the eighteenth century, the same possibility was mentioned by [[Isaac Newton]] in the "[[General Scholium]]" that concludes his ''[[Philosophiae Naturalis Principia Mathematica|Principia]]''. Making a comparison to the Sun's planets, he wrote "And if the fixed stars are the centres of similar systems, they will all be constructed according to a similar design and subject to the dominion of ''One''."<ref>{{Cite book |last = Newton|first = Isaac|author2 = I. Bernard Cohen |author3= Anne Whitman|title = The Principia: A New Translation and Guide|publisher = University of California Press|date=1999|orig-year=1713|page = 940|isbn = 978-0-520-08816-0}}</ref>

In 1938, D.Belorizky demonstrated that it was realistic to search for exo-Jupiters by using [[transit method|transit photometry]].<ref>[https://ui.adsabs.harvard.edu/abs/1938LAstr..52..359B/abstract Le Soleil, Etoile Variable],  D.Belorizky, 1938</ref>

In 1952, more than 40 years before the first [[hot Jupiter]] was discovered, [[Otto Struve]] wrote that there is no compelling reason that 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-Jupiter]]s in short orbits.<ref>{{cite journal|title= Proposal for a project of high-precision stellar radial velocity work|last=Struve|first= Otto |journal= The Observatory|volume=72|pages=199–200 |year=1952|bibcode = 1952Obs....72..199S }}</ref>

=== Discredited claims ===
Claims of exoplanet detections have been made since the nineteenth century. Some of the earliest involve the [[binary star]] [[70 Ophiuchi]]. 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.<ref>{{Cite journal|author=Jacob, W. S.|date=1855|title=On Certain Anomalies presented by the Binary Star 70 Ophiuchi|url=https://books.google.com/books?id=pQsAAAAAMAAJ&pg=PA228|journal=[[Monthly Notices of the Royal Astronomical Society]]|volume=15 |issue=9|pages=228–230|bibcode=1855MNRAS..15..228J |doi=10.1093/mnras/15.9.228|doi-access=free}}</ref> In the 1890s, [[Thomas Jefferson Jackson See|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&nbsp;Ophiuchi system with a 36-year [[orbital period|period]] around one of the stars.<ref>{{cite journal |last=See |first=T. J. J. |author-link=Thomas Jefferson Jackson See |year=1896 |title=Researches on the orbit of 70 Ophiuchi, and on a periodic perturbation in the motion of the system arising from the action of an unseen body |journal=The Astronomical Journal |volume=16 |pages=17–23 |doi=10.1086/102368 |bibcode=1896AJ.....16...17S}}</ref> However, [[Forest Ray Moulton]] published a paper proving that a three-body system with those orbital parameters would be highly unstable.<ref>{{Cite journal|author=Sherrill, T. J.|date=1999|journal=[[Journal for the History of Astronomy]]|title=A Career of Controversy: The Anomaly of T. J. J. See|url=http://www.shpltd.co.uk/jha.pdf|volume=30 |issue=98 |pages=25–50|bibcode=1999JHA....30...25S |doi=10.1177/002182869903000102|s2cid=117727302}}</ref>

Multiple claims have been made that [[61 Cygni]] might have a planetary system. [[Kaj Aage Gunnar Strand|Kaj Strand]] of the Sproul Observatory in 1942 observed tiny but systematic variations in the orbital motions of 61 Cygni A and B, suggesting that a third body of about 16 Jupiter masses must be orbiting 61 Cygni A.<ref>{{cite journal
 | last=Strand | first=K. Aa.
 | title=61 Cygni as a Triple System
 | journal=Publications of the Astronomical Society of the Pacific
 | date=1943 | volume=55 | issue=322 | pages=29–32
 | bibcode=1943PASP...55...29S
 | doi=10.1086/125484 | doi-access=free}}</ref> Multiple further claims were made, but more recent observations have yet to find confirmation. More information at [[61 Cygni#Claims_of_a_planetary_system| 61 Cygni:Claims of a planetary system]].  

Around the same time that 61 Cygni was being investigated, similar claims about the presence of exoplanets were made about Lalande 21185: [[Lalande_21185#Past_claims_of_planets]].

During the 1950s and 1960s, [[Peter van de Kamp]] of [[Swarthmore College]] made another prominent series of detection claims, this time for planets orbiting [[Barnard's Star]].<ref>{{Cite journal|author=van de Kamp, P. |date=1969|title=Alternate dynamical analysis of Barnard's star|journal=[[Astronomical Journal]]|volume=74 |pages=757–759|doi=10.1086/110852|bibcode=1969AJ.....74..757V}}</ref> Astronomers now generally regard all early reports of detection as erroneous.<ref name="boss_book p31">{{Cite book|last = Boss|first = Alan|title = The Crowded Universe: The Search for Living Planets|publisher = Basic Books|date = 2009|pages = 31–32|isbn = 978-0-465-00936-7}}</ref>

In 1991, [[Andrew Lyne]], [[Matthew Bailes|M. Bailes]] and S. L. Shemar claimed to have discovered a [[pulsar planet]] in orbit around [[PSR 1829-10]], using [[pulsar timing]] variations.<ref name="LyneBailes">{{Cite journal | last1 = Bailes | first1 = M. | last2 = Lyne | first2 = A. G. | author-link2 = Andrew Lyne| last3 = Shemar | first3 = S. L. | doi = 10.1038/352311a0 |bibcode=1991Natur.352..311B| title = A planet orbiting the neutron star PSR1829–10 | journal = Nature | volume = 352 | issue = 6333 | pages = 311–313 | year = 1991 | s2cid = 4339517 }}</ref> The claim briefly received intense attention, but Lyne and his team soon retracted it.<ref name="LyneRetraction">{{Cite journal | doi = 10.1038/355213b0| title = No planet orbiting PS R1829–10| journal = Nature| volume = 355| issue = 6357| page = 213| year = 1992| last1 = Lyne | first1 = A. G.| last2 = Bailes | first2 = M. | bibcode = 1992Natur.355..213L| s2cid = 40526307| doi-access = free}}</ref>

=== Confirmed discoveries ===
{{Main|Discoveries of exoplanets}}
{{See also|List of exoplanet firsts}}
[[File:The Star AB Pictoris and its Companion - Phot-14d-05-normal.jpg|thumb|300px|[[Coronagraph]]ic image of [[AB Pictoris]] showing a companion (bottom left), which is either a brown dwarf or a massive planet. The data were obtained on 16 March 2003 with [[List of instruments at the Very Large Telescope|NACO]] on the [[Very Large Telescope|VLT]], using a 1.4 arcsec occulting mask on top of AB Pictoris.]]
{{multiple image
| align             = right
| direction         = vertical
| width             = 300
| image1            = 444226main exoplanet20100414-a-full.jpg
| alt1              = False-color, star-subtracted, direct image using a vortex coronagraph of 3 exoplanets around star HR8799
| caption1          = The three known planets of the star [[HR 8799]], as imaged by the [[Hale Telescope]]. The light from the central star was blanked out by a [[vector vortex coronagraph]].
| image2            = Brown dwarf 2M J044144 and planet.jpg
| alt2              = Hubble image of brown dwarf 2MASS J044144 and its 5–10 Jupiter-mass companion, before and after star-subtraction
| caption2          = [[2MASS J044144]] is a [[brown dwarf]] with a companion about 5–10 times the mass of Jupiter. It is not clear whether this companion object is a [[sub-brown dwarf]] or a planet.
}}

As of {{Extrasolar planet counts|asof}}, a total of {{Extrasolar planet counts|planet_count|source=NEA}} confirmed exoplanets are listed in the [[NASA Exoplanet Archive]], including a few that were confirmations of controversial claims from the late 1980s.{{Extrasolar planet counts|ref}} The first published discovery to receive subsequent confirmation was made in 1988 by the Canadian astronomers Bruce Campbell, G. A. H. Walker, and Stephenson Yang of the [[University of Victoria]] and the [[University of British Columbia]].<ref name="Campbell">{{Cite journal | last1 = Campbell | first1 = B. | last2 = Walker | first2 = G. A. H. | last3 = Yang | first3 = S. | title = A search for substellar companions to solar-type stars | doi = 10.1086/166608 | journal = The Astrophysical Journal | volume = 331 | page = 902 | year = 1988 | bibcode=1988ApJ...331..902C| doi-access = free }}</ref> Although they were cautious about claiming a planetary detection, their radial-velocity observations suggested that a planet orbits the star [[Gamma Cephei]]. Partly because the observations were at the very limits of instrumental capabilities at the time, astronomers remained skeptical for several years about this and other similar observations. It was thought some of the apparent planets might instead have been [[brown dwarf]]s, objects intermediate in mass between planets and stars. In 1990, additional observations were published that supported the existence of the planet orbiting Gamma Cephei,<ref>{{Cite journal|last1=Lawton |first1=A. T.|last2=Wright |first2=P.|date=1989|title=A planetary system for Gamma Cephei?|journal=[[Journal of the British Interplanetary Society]]|volume=42|pages=335–336|bibcode=1989JBIS...42..335L}}</ref> but subsequent work in 1992 again raised serious doubts.<ref name="Walker">{{Cite journal|last1=Walker |first1=G. A. H|date=1992|title=Gamma Cephei&nbsp;– Rotation or planetary companion?|journal=[[Astrophysical Journal Letters]]|volume=396|issue=2|pages=L91–L94|doi=10.1086/186524|bibcode=1992ApJ...396L..91W|last2=Bohlender |first2=D. A.|last3=Walker |first3=A. R.|last4=Irwin |first4=A. W.|last5=Yang |first5=S. L. S.|last6=Larson |first6=A.|doi-access=free}}</ref> Finally, in 2003, improved techniques allowed the planet's existence to be confirmed.<ref>{{Cite journal|last1=Hatzes |first1=A. P.|last2=Cochran |first2=William D.|title=A Planetary Companion to Gamma Cephei A|journal=[[Astrophysical Journal]]|date=2003|volume=599|issue=2|pages=1383–1394|doi =10.1086/379281|bibcode=2003ApJ...599.1383H|arxiv = astro-ph/0305110|last3=Endl|first3=Michael|last4=McArthur|first4=Barbara|last5=Paulson|first5=Diane B.|last6=Walker|first6=Gordon A. H.|last7=Campbell|first7=Bruce|last8=Yang|first8=Stephenson|s2cid=11506537}}</ref>

On 9 January 1992, radio astronomers [[Aleksander Wolszczan]] and [[Dale Frail]] announced the discovery of two planets orbiting the [[millisecond pulsar]] [[PSR B1257+12|PSR 1257+12]] based on the variability of timing of the pulses.<ref name="Wolszczan">{{Cite journal | last1 = Wolszczan | first1 = A. |bibcode=1992Natur.355..145W| last2 = Frail | first2 = D. A. | doi = 10.1038/355145a0 | title = A planetary system around the millisecond pulsar PSR1257 + 12 | journal = Nature | volume = 355 | issue = 6356 | pages = 145–147 | year = 1992 | s2cid = 4260368 }}</ref> This discovery was confirmed, and is generally considered to be the first definitive detection of exoplanets. Follow-up observations solidified these results, and confirmation of a third planet in 1994 revived the topic in the popular press.<ref>{{cite news | url=http://tech.mit.edu/V114/N22/psr.22w.html | title=Scientists Uncover Evidence of New Planets Orbiting Star | newspaper=Los Angeles Times via [[The Tech (newspaper)|The Tech Online]] | first=Robert | last=Holtz | date=22 April 1994 | access-date=20 April 2012 | archive-date=17 May 2013 | archive-url=https://web.archive.org/web/20130517225034/http://tech.mit.edu/V114/N22/psr.22w.html | url-status=dead }}</ref> These pulsar planets are thought to have formed from the unusual remnants of the [[supernova]] that produced the pulsar, in a second round of planet formation, or else to be the [[Chthonian planet|remaining rocky cores]] of [[gas giant]]s that somehow survived the supernova and then decayed into their current orbits. As pulsars are aggressive stars, it was considered unlikely at the time that a planet could form in their orbit.<ref>{{cite book |last= Rodriguez Baquero|first= Oscar Augusto|date= 2017|title= La presencia humana más allá del sistema solar|trans-title= Human presence beyond the solar system|url= |language= Spanish|page=29|location= |publisher= RBA|isbn=978-84-473-9090-8}}</ref>

In the early 1990s, a group of astronomers led by [[Donald Backer]], who were studying what they thought was a binary pulsar ([[PSR B1620−26 b]]), determined that a third object was needed to explain the observed [[Doppler shift]]s. Within a few years, the gravitational effects of the planet on the orbit of the pulsar and [[white dwarf]] had been measured, giving an estimate of the mass of the third object that was too small to be a star. The conclusion that the third object was a planet was announced by [[Stephen Thorsett]] and his collaborators in 1993.<ref name="STScI">{{cite web | title=Oldest Known Planet Identified | work=[[HubbleSite]] | url=http://hubblesite.org/newscenter/newsdesk/archive/releases/2003/19/ | access-date=2006-05-07}}</ref>

On 6 October 1995, [[Michel Mayor]] and [[Didier Queloz]] of the [[University of Geneva]] announced the first definitive detection of [[51 Pegasi b|an exoplanet]] orbiting a [[main sequence|main-sequence]] star, nearby [[G-type star]] [[51 Pegasi]].<ref name="Wenz"/><ref name="Mayor">{{Cite journal | doi = 10.1038/378355a0| title = A Jupiter-mass companion to a solar-type star| journal = Nature| volume = 378| issue = 6555| pages = 355–359| year = 1995| last1 = Mayor | first1 = M. | last2 = Queloz | first2 = D. | bibcode = 1995Natur.378..355M| s2cid = 4339201}}</ref><ref name=gibn>{{cite journal|last1=Gibney|first1=Elizabeth|title=In search of sister earths|journal=Nature|date=18 December 2013|volume=504|issue=7480|pages=357–365|doi=10.1038/504357a|pmid=24352276|bibcode = 2013Natur.504..357. |doi-access=free}}</ref> This discovery, made at the [[Observatoire de Haute-Provence]], ushered in the modern era of exoplanetary discovery, and was recognized by a share of the 2019 [[Nobel Prize in Physics]]. Technological advances, most notably in high-resolution [[spectroscopy]], led to the rapid detection of many new exoplanets: astronomers could detect exoplanets indirectly by measuring their [[gravity|gravitational]] influence on the motion of their host stars. More extrasolar planets were later detected by observing the variation in a star's apparent luminosity as an orbiting planet transited in front of it.<ref name="Wenz"/>

Initially, the most known exoplanets were massive planets that orbited very close to their parent stars. Astronomers were surprised by these "[[hot Jupiter]]s", because theories of [[Nebular hypothesis#Formation of planets|planetary formation]] had indicated that giant planets should only form at large distances from stars. But eventually more planets of other sorts were found, and it is now clear that hot Jupiters make up the minority of exoplanets.<ref name="Wenz">{{cite journal |last1=Wenz |first1=John |title=Lessons from scorching hot weirdo-planets |journal=Knowable Magazine |publisher= Annual Reviews |date=10 October 2019 |doi=10.1146/knowable-101019-2|doi-access=free |url=https://knowablemagazine.org/article/physical-world/2019/hot-jupiter-formation-theories |access-date=4 April 2022 |language=en}}</ref> In 1999, [[Upsilon Andromedae]] became the first main-sequence star known to have multiple planets.<ref name="Lissauer_multiple99">{{Cite journal | doi = 10.1038/19409| year = 1999| last1 = Lissauer | first1 = J. J. | title = Three planets for Upsilon Andromedae| journal = Nature| volume = 398| issue = 6729| page = 659| bibcode = 1999Natur.398..659L| s2cid = 204992574| doi-access = free}}</ref> [[Kepler-16]] contains the first discovered planet that orbits a binary main-sequence star system.<ref name=Doyle>{{Cite journal | doi = 10.1126/science.1210923| pmid = 21921192| title = Kepler-16: A Transiting Circumbinary Planet| journal = Science| volume = 333| issue = 6049| pages = 1602–1606| year = 2011| last1 = Doyle | first1 = L. R.| last2 = Carter | first2 = J. A.| last3 = Fabrycky | first3 = D. C.| last4 = Slawson | first4 = R. W.| last5 = Howell | first5 = S. B.| last6 = Winn | first6 = J. N.| last7 = Orosz | first7 = J. A.| last8 = Prša | first8 = A.| last9 = Welsh | first9 = W. F.| last10 = Quinn | first10 = S. N.| last11 = Latham | first11 = D.| last12 = Torres | first12 = G.| last13 = Buchhave | first13 = L. A.| last14 = Marcy | first14 = G. W.| last15 = Fortney | first15 = J. J.| last16 = Shporer | first16 = A.| last17 = Ford | first17 = E. B.| last18 = Lissauer | first18 = J. J.| last19 = Ragozzine | first19 = D.| last20 = Rucker | first20 = M.| last21 = Batalha | first21 = N.| last22 = Jenkins | first22 = J. M.| last23 = Borucki | first23 = W. J.| last24 = Koch | first24 = D.| last25 = Middour | first25 = C. K.| last26 = Hall | first26 = J. R.| last27 = McCauliff | first27 = S.| last28 = Fanelli | first28 = M. N.| last29 = Quintana | first29 = E. V.| last30 = Holman | first30 = M. J.| display-authors = etal| bibcode = 2011Sci...333.1602D|arxiv = 1109.3432 | s2cid = 206536332}}</ref>

On 26 February 2014, NASA announced the discovery of 715 newly verified exoplanets around 305 stars by the [[Kepler (spacecraft)|''Kepler'' Space Telescope]]. These exoplanets were checked using a statistical technique called "verification by multiplicity".<ref name="kepler1700">{{cite web |last1=Johnson |first1=Michele |last2=Harrington |first2=J.D. |title=NASA's Kepler Mission Announces a Planet Bonanza, 715 New Worlds |url=http://www.nasa.gov/ames/kepler/nasas-kepler-mission-announces-a-planet-bonanza/ |date=26 February 2014 |work=[[NASA]] |access-date=26 February 2014 |archive-date=26 February 2014 |archive-url=https://web.archive.org/web/20140226202703/http://www.nasa.gov/ames/kepler/nasas-kepler-mission-announces-a-planet-bonanza/ |url-status=dead }}</ref><ref name="space.com">{{cite web|last=Wall|first=Mike|title=Population of Known Alien Planets Nearly Doubles as NASA Discovers 715 New Worlds|url=http://www.space.com/24824-alien-planets-population-doubles-nasa-kepler.html|date=26 February 2014|access-date=27 February 2014|publisher=space.com}}</ref><ref name="bbcnews">{{cite news |author=Amos |first=Jonathan |date=26 February 2014 |title=Kepler telescope bags huge haul of planets |url=https://www.bbc.co.uk/news/science-environment-26362433 |access-date=27 February 2014 |work=BBC News}}</ref> Before these results, most confirmed planets were gas giants comparable in size to Jupiter or larger because they were more easily detected, but the ''Kepler'' planets are mostly between the size of Neptune and the size of Earth.<ref name="kepler1700" />

On 23 July 2015, NASA announced [[Kepler-452b]], a near-Earth-size planet orbiting the habitable zone of a G2-type star.<ref name="NASA-20150723">{{cite web |last1=Johnson |first1=Michelle |last2=Chou |first2=Felicia |title=NASA's Kepler Mission Discovers Bigger, Older Cousin to Earth |url=http://www.nasa.gov/press-release/nasa-kepler-mission-discovers-bigger-older-cousin-to-earth |date=23 July 2015 |work=[[NASA]]}}</ref>

On 6 September 2018, NASA discovered an exoplanet about 145 light years away from Earth in the constellation Virgo.<ref name="Oddball">{{Cite news |last=NASA |title=Discovery alert! Oddball planet could surrender its secrets |url=https://exoplanets.nasa.gov/news/1521/discovery-alert-oddball-planet-could-surrender-its-secrets/ |access-date=28 November 2018 |work=Exoplanet Exploration: Planets Beyond our Solar System}}</ref> This exoplanet, Wolf 503b, is twice the size of Earth and was discovered orbiting a type of star known as an "Orange Dwarf". Wolf 503b completes one orbit in as few as six days because it is very close to the star. Wolf 503b is the only exoplanet that large that can be found near the so-called [[small planet radius gap]]. The gap, sometimes called the Fulton gap,<ref name="Oddball"/><ref>{{Cite journal |last1=Fulton |first1=Benjamin J. |last2=Petigura |first2=Erik A. |last3=Howard |first3=Andrew W. |last4=Isaacson |first4=Howard |last5=Marcy |first5=Geoffrey W. |last6=Cargile |first6=Phillip A. |last7=Hebb |first7=Leslie |last8=Weiss |first8=Lauren M. |last9=Johnson |first9=John Asher |last10=Morton |first10=Timothy D. |last11=Sinukoff |first11=Evan |last12=Crossfield |first12=Ian J. M. |last13=Hirsch |first13=Lea A. |date=2017-09-01 |title=The California-Kepler Survey. III. A Gap in the Radius Distribution of Small Planets* |journal=The Astronomical Journal |volume=154 |issue=3 |pages=109 |doi=10.3847/1538-3881/aa80eb |doi-access=free |arxiv=1703.10375 |bibcode=2017AJ....154..109F |issn=0004-6256}}</ref> is the observation that it is unusual to find exoplanets with sizes between 1.5 and 2 times the radius of the Earth.<ref>{{Cite web |title=Radius Gap |url=https://sites.astro.caltech.edu/~fdai/radius_gap.html |access-date=2024-04-03 |website=sites.astro.caltech.edu}}</ref>

In January 2020, scientists announced the discovery of [[TOI 700 d]], the first Earth-sized planet in the habitable zone detected by TESS.<ref>{{Cite web|url=https://www.midilibre.fr/2020/01/07/toi-700d-une-planete-de-la-taille-de-la-terre-decouverte-dans-une-zone-habitable,8645004.php|title=[VIDEO] TOI 700d : une planète de la taille de la Terre découverte dans une "zone habitable"|website=midilibre.fr|language=fr|access-date=2020-04-17}}</ref>

=== Candidate discoveries ===
As of January 2020, NASA's [[Kepler (spacecraft)|''Kepler'']] and [[Transiting Exoplanet Survey Satellite|TESS]] missions had identified 4374 planetary candidates yet to be confirmed,<ref>{{Cite web|url=https://exoplanetarchive.ipac.caltech.edu/docs/counts_detail.html|title=Exoplanet and Candidate Statistics|publisher=NASA Exoplanet Archive, California Institute of Technology|access-date=2020-01-17}}</ref> several of them being nearly Earth-sized and located in the habitable zone, some around Sun-like stars.<ref name="keplersite">{{cite web |author=Colen |first=Jerry |date=4 November 2013 |title=Kepler |url=http://www.nasa.gov/mission_pages/kepler/main/index.html |archive-url=https://web.archive.org/web/20131105082102/http://www.nasa.gov/mission_pages/kepler/main/index.html |archive-date=5 November 2013 |access-date=4 November 2013 |website=nasa.gov |publisher=NASA}}</ref><ref name="usher">{{cite web |last1=Harrington |first1=J. D. |last2=Johnson |first2=M. |date=4 November 2013 |title=NASA Kepler Results Usher in a New Era of Astronomy |url=http://www.nasa.gov/press/2013/november/nasa-kepler-results-usher-in-a-new-era-of-astronomy/}}</ref><ref name="NASA-ExoplanetArch">{{cite web|title=NASA's Exoplanet Archive KOI table|url=http://exoplanetarchive.ipac.caltech.edu/cgi-bin/ExoTables/nph-exotbls?dataset=cumulative|publisher=NASA|access-date=28 February 2014|archive-url=https://archive.today/20140226203336/http://exoplanetarchive.ipac.caltech.edu/cgi-bin/ExoTables/nph-exotbls?dataset=cumulative|archive-date=26 February 2014|url-status=dead}}</ref>
{{multiple image
| header            = Exoplanet populations – June 2017<!--
  --><ref name="SP-20170619">{{cite web |last=Lewin |first=Sarah |title=NASA's Kepler Space Telescope Finds Hundreds of New Exoplanets, Boosts Total to 4,034 |url=https://www.space.com/37242-nasa-kepler-alien-planets-habitable-worlds-catalog.html |date=19 June 2017 |work=[[NASA]] |access-date=19 June 2017}}</ref><!--
  --><ref name="NYT-20170619">{{cite news |last=Overbye |first=Dennis |author-link=Dennis Overbye |title=Earth-Size Planets Among Final Tally of NASA's Kepler Telescope |url=https://www.nytimes.com/2017/06/19/science/kepler-planets-earth-like-census.html |archive-url=https://ghostarchive.org/archive/20220101/https://www.nytimes.com/2017/06/19/science/kepler-planets-earth-like-census.html |archive-date=2022-01-01 |url-access=limited |date=19 June 2017 |work=The New York Times}}{{cbignore}}</ref>
| align             = center
| caption_align     = center
| direction         = horizontal
| width             = 333
| image1            = ExoplanetPopulations-20170616.png
| alt1              = 
| caption1          = Exoplanet populations; colors indicate detection method
| image2            = SmallPlanetsComeInTwoSizes-20170619.png
| alt2              = 
| caption2          = Small planets come in two sizes
| image3            = KeplerHabitableZonePlanets-20170616.png
| alt3              = 
| caption3          = Kepler habitable zone planets
}}

In September 2020, astronomers reported evidence, for the first time, of an [[extragalactic planet]], [[M51-ULS-1b]], detected by eclipsing a bright [[Astrophysical X-ray source|X-ray source]] (XRS), in the [[Whirlpool Galaxy]] (M51a).<ref name="NS-20200923">{{cite news |last=Crane |first=Leah |title=Astronomers may have found the first planet in another galaxy |url=https://www.newscientist.com/article/2255431-astronomers-may-have-found-the-first-planet-in-another-galaxy/ |date=23 September 2020 |work=[[New Scientist]] |access-date=25 September 2020 }}</ref><ref name="ARX-20200918">{{cite arXiv |author=Di Stafano, R. |display-authors=et al. |title=M51-ULS-1b: The First Candidate for a Planet in an External Galaxy |date=18 September 2020 |class=astro-ph.HE |eprint=2009.08987 }}</ref>