View source for List of former planets

{{Short description|none}}
This is a list of [[astronomical object]]s formerly widely considered ''[[planet]]s'' under any of the various definitions of this word in the history of astronomy. As the [[definition of planet|definition of ''planet'']] has evolved, the [[wikt:en:de facto#English|de facto]] and [[wikt:en:de jure#English|de jure]] definitions of [[wikt:en:planet#English|planet]] have changed over the millennia. As of 2024, there are [[IAU definition of planet|eight official planets]] in the [[Solar System]] per the [[International Astronomical Union]] (IAU),<ref>{{cite news |url=http://www.iau.org/static/resolutions/Resolution_GA26-5-6.pdf |title=Definition of a Planet in the Solar System: Resolutions 5 and 6 |date=August 24, 2006 |work=IAU 2006 General Assembly |publisher=International Astronomical Union |access-date=January 26, 2008 |author=IAU}}</ref> which has also established a definition for [[exoplanet]]s. Several objects formerly considered exoplanets have been found actually to be [[star]]s or [[brown dwarf]]s.

==Background==
Throughout antiquity, several astronomical objects were considered [[Classical Planet]]s, meaning "wandering stars", not all of which are now considered planets. The [[natural satellite|moons]] discovered around [[Jupiter]], [[Saturn]] and [[Uranus]] after the advent of the telescope were also initially considered planets by some. The development of more powerful telescopes resulted in the discovery of the [[asteroid]]s, which were initially considered planets. Then [[Pluto]], the first [[Trans-Neptunian Object]], was discovered. More Trans-Neptunian Objects of the [[Kuiper Belt]] were found with the help of electronic imaging. One of these, [[Eris (dwarf planet)|Eris]], was widely hailed as a "new planet", which prompted the [[IAU definition of planet|2006 recategorization of solar system bodies]].

Some planetary scientists reject the 2006 definition of planet, and thus would still consider some of the objects on this list to be planets under a [[geophysical definition of planet|geophysical definition]]. See the [[list of gravitationally rounded objects of the Solar System]] for a list of geophysical planets.

==List==

{|class="wikitable sortable"
|-
|+ Former planets of the Solar System
|-
!class="unsortable"| <!-- Astrological and astronomical symbol -->
!| Former planet
!| {{tooltip|Discovery|discovery date, planet status conferment}}
!| {{tooltip|Removal|planet status removed}}
!| Current status
!class="unsortable"| <!-- photo / map / diagram -->
!class="unsortable" width=100%| Notes
!class="unsortable"| <!-- refs -->
|-
||
|| {{sort|Morning Star|[[Phosphorus (morning star)|The&nbsp;Morning&nbsp;Star]]}}<ref group=NB name=Aphrodite>It is an aspect of the planet Venus.</ref>
|| {{sort|-9999|Antiquity}}
|| {{sort|-400|Antiquity}}
|rowspan=2| {{sort|Aspect|Aspects of [[Venus]]}}
|| [[File:Saturn, Moon, Venus and Mercury at dawn - 10 Dec. 2012.jpg|50px]]
|rowspan=2| "Phosphorus", the Morning Star of Greek antiquity (''Eosphorus'', the Dawn-Bringer; called "Lucifer" by the Romans), and "Hesperus", the Evening Star (called "Vesper" by the Romans), were later identified as a single planet, [[Venus (planet)|Venus]] (Aphrodite).
| rowspan=2|
<ref name="10.2307/2182495"> {{cite journal |title= Hesperus and Phosphorus |journal= The Philosophical Review |author= Leonard Linsky |volume= 68 |number= 4 |date= October 1959 |pages= 515–518 |doi= 10.2307/2182495 |jstor= 2182495 }} 
</ref><ref name=StarGazer-1628>
{{cite episode |url= http://www.jackstargazer.com/scripts_feb2009.html |title= The Great Cosmic Light Called Hesperus, Brother Of Lucifer, Reaches Greatest Brilliancy |series= Star Gazer |number= 09-07 (1628) |date= February 2009 }} 
</ref>
|-
||
|| {{sort|Evening Star|[[Hesperus|The&nbsp;Evening&nbsp;Star]]}}<ref group=NB name=Aphrodite /> 
|| {{sort|-9999|Antiquity}}
|| {{sort|-400|Antiquity}}
|| [[File:Winterabend im Dorf Cyriaxweimar in Elnhausen-Michelbacher Senke mit Venus am Nachthimmel, Radroute von Marburg-Stadtwald 2016-12-30.jpg|50px]]
|-
|| 
|| Apollo<ref group=NB name=Apollo>It is an aspect of the planet Mercury.</ref>
|| {{sort|-9999|Antiquity}}
|| {{sort|-300|Antiquity}}
|| {{sort|Aspect|Aspect of [[Mercury (planet)|Mercury]]}}
|| [[File:Merkur04122019.png|50px]]
|| Like the Morning and Evening Stars, Mercury was deemed to be a distinct planet when it was visible during daytime, and dedicated to [[Apollo]] by the Greeks. Eventually, in the [[4th century BC]], Mercury and Apollo were found to be one and the same.
|| <ref>{{Cite web|url=https://www.space.com/29265-mercury-planet-facts-for-skywatchers.html|title=Planet Mercury: Some Surprising Facts for Skywatchers|website=[[Space.com]]|date=29 April 2015}}</ref>
|-
|| [[File:Sun symbol (fixed width).svg|50px|alt=☉]]
|| [[Sun]]
|| {{sort|-9999|Antiquity}}
|| 1543
|| [[Star]]
|| [[File:Sun white.jpg|50px]]
|| In antiquity, it was believed that the Sun and all the planets orbit the Earth. Thus the Sun was categorised as a planet. Following the acceptance of the [[Copernican model]], it was recognized that the planets (including Earth) orbit the Sun, and it was no longer regarded as a planet. Subsequent discoveries show that the Sun is a star.
|| 
<ref name=UniverseToday-DiffGeocentricHeliocentric>{{cite news |url= http://www.universetoday.com/36487/difference-between-geocentric-and-heliocentric/ |title= What Is The Difference Between the Geocentric and Heliocentric Models of the Solar System? |date= 23 December 2015 |work= Universe Today |author= Elizabeth Howell }}
</ref><ref name=NASAEarthObs-OrbitsHist-pg1>
{{cite web |url= http://earthobservatory.nasa.gov/Features/OrbitsHistory/page1.php |title= Planetary Motion: The History of an Idea That Launched the Scientific Revolution |author= Holli Riebeek |date= 7 July 2009 |work= The Science: Orbital Mechanics |publisher= NASA Earth Observatory }}
</ref><ref name=Blackman-AST104-Copernican>
{{cite web |url= http://www.pas.rochester.edu/~blackman/ast104/copernican9.html |title= The Copernican Model: A Sun-Centered Solar System  |work= Astronomy 104 – The Solar System |date= 2006 |author= Eric G. Blackman |publisher= University of Rochester, School of Arts and Sciences, Department of Physics and Astronomy }} 
</ref>
|-
|| [[File:Moon decrescent symbol (fixed width).svg|50px|alt=☾]]
|| [[Moon]]
|| {{sort|-9999|Antiquity}}
|| 1543
|| {{sort|Moon|[[Natural satellite|Moon]] of [[Earth]]}}
|| [[File:FullMoon2010.jpg|50px]]
|| Following the acceptance of the [[Copernican model]], planets were defined as objects which orbit the Sun. Since the Moon can be said to orbit the Earth, it was no longer regarded as a planet, but this is debated; see [[double planet]].
|| 
<ref name=UniverseToday-DiffGeocentricHeliocentric/><ref name=NASAEarthObs-OrbitsHist-pg1/><ref name=Blackman-AST104-Copernican/>
|-
|| 
|| [[Io (moon)|Io]]
|| 1610
|| 1700s
| rowspan=4| {{sort|Moon|[[Moons of Jupiter]]}}
|| [[File:Io_highest_resolution_true_color.jpg|50px]]
| rowspan=4|Originally presented as satellite planets orbiting the planet [[Jupiter]]. Planetary status later rescinded, leaving them only as satellites. [[Ganymede (moon)|Ganymede]] is the largest satellite in the Solar System, and is slightly larger than [[Mercury (planet)|Mercury]], but is about half as massive.
| rowspan=4|
<ref name=SidereusNuncius>
{{cite journal |title= Sidereus Nuncius |author= Galileo Galilei |year= 1610 |language=la}}
</ref><ref name=Rice-GalileoPrj-JupiterSats>
{{cite web |url= http://galileo.rice.edu/sci/observations/jupiter_satellites.html |title= Satellites of Jupiter |date= 1995 |author= Al Van Helden |work= The Galileo Project |publisher= Rice University }}
</ref><ref name=SolarViews-Galileans>
{{cite web |url= http://solarviews.com/eng/galdisc.htm |title= The Discovery of the Galilean Satellites |publisher= Views of the Solar System |author=  Calvin J. Hamilton |date= 2009 }}
</ref>
<ref name=IIRS-2016-12-31>
{{cite journal |url= http://inference-review.com/article/the-provencal-humanists-and-copernicus |title= Montaigne, Peiresc, Gassendi, and Cassini - The Provençal Humanists and Copernicus |author= Jean-Pierre Luminet |volume= 2 |number= 4 |journal= Inference: International Review of Science |date= 31 December 2016 }}
</ref><ref name=NASAEarthObs-OrbitsHist-pg1/><ref name=Blackman-AST104-Copernican/>
|-
|| 
|| [[Europa (moon)|Europa]]
|| 1610
|| 1700s
|| [[File:Europa_in_natural_color.png|50px]]
|-
|| 
|| [[Ganymede (moon)|Ganymede]]
|| 1610
|| 1700s
|| [[File:Ganymede_-_Perijove_34_Composite.png|50px]]
|-
|| 
|| [[Callisto (moon)|Callisto]]
|| 1610
|| 1700s
|| [[File:Callisto_-_July_8_1979_(38926064465).jpg|50px]]
|-
|| 
|| [[Titan (moon)|Titan]] 
|| 1656
|| 1700s
| rowspan=5| {{sort|Moon|[[Moons of Saturn]]}}
|| [[File:Lakes Through the Haze.jpg|50px]]
| rowspan=5|Originally presented as satellite planets orbiting the planet [[Saturn]]. Planetary status later rescinded, leaving them only as satellites. [[Titan (moon)|Titan]] is the second largest satellite in the Solar System, and is slightly larger than [[Mercury (planet)|Mercury]], but less massive.
||<ref name=SystemaSaturnium>
{{cite journal |title= Systema Saturnium |author= Cristiani Hugenii (Christiaan Huygens) |year= 1659 |language=la}}
</ref><ref name=NASAEarthObs-OrbitsHist-pg1/><ref name=Blackman-AST104-Copernican/>  
|-
|| 
|| [[Iapetus (moon)|Iapetus]] 
|| 1671
|| 1700s
|| [[File:Japeto es una luna de saturno.jpg|50px]]
| rowspan=2|
<ref name=Cassini-1673>
{{cite journal |title= Découverte de deux nouvelles planètes autour de Saturne |author= Jean-Dominique Cassini (Giovanni Domenico Cassini) |year= 1673 |publisher= Paris Observatory |language=fr}}
</ref><ref name=IIRS-2016-12-31/>
<ref name=NASAEarthObs-OrbitsHist-pg1/><ref name=Blackman-AST104-Copernican/>
|-
|| 
|| [[Rhea (moon)|Rhea]] 
|| 1672
|| 1700s
|| [[File:PIA07763_Rhea_full_globe5.jpg|50px]]
|-
|| 
|| [[Tethys (moon)|Tethys]] 
|| 1684
|| 1700s
|| [[File:PIA18317-SaturnMoon-Tethys-Cassini-20150411.jpg|50px]]
| rowspan=2|
<ref name="10.1098/rstl.1686.0013">
{{cite journal |doi= 10.1098/rstl.1686.0013 |author = Jean-Dominique Cassini (Giovanni Domenico Cassini) |year= 1686–1692 |title= An Extract of the Journal Des Scavans. Of April 22 st. N. 1686. Giving an Account of Two New Satellites of Saturn, Discovered Lately by Mr. Cassini at the Royal Observatory at Paris |journal= Philosophical Transactions of the Royal Society of London |volume= 16 |issue= 179–191 |pages= 79–85 |jstor= 101844 |bibcode = 1686RSPT...16...79C |doi-access= free }} 
</ref><ref name=IIRS-2016-12-31/>
<ref name=NASAEarthObs-OrbitsHist-pg1/><ref name=Blackman-AST104-Copernican/>
|-
|| 
|| [[Dione (moon)|Dione]] 
|| 1684
|| 1700s
|| [[File:Dione_in_natural_light.jpg|50px]]
|-
|| 
|| [[Titania (moon)|Titania]] 
|| 1787
||1700s
| rowspan=2| {{sort|Moon|[[Moons of Uranus]]}}
||[[File:Titania (moon) color, edited.jpg|50x50px]]
| rowspan=2|Originally presented as satellite planets orbiting the planet [[Uranus]].<ref>{{cite journal| doi = 10.1098/rstl.1787.0016| last = Herschel | first = W. S.| author-link = William Herschel| title = An Account of the Discovery of Two Satellites Revolving Round the Georgian Planet| journal = Philosophical Transactions of the Royal Society of London| volume = 77| pages = 125–129| year = 1787| jstor = 106717| doi-access = free |quote=And the heavens now displayed the original of my drawing, by shewing, in the situation I had delineated them, ''The Georgian Planet attended by two satellites''.<br><br>I confess that this scene appeared to me with additional beauty, as the little secondary planets seemed to give a dignity to the primary one, which raises it into a more conspicuous situation among the great bodies of our solar system.}}</ref> Planetary status later rescinded, leaving them only as satellites.
||
|-
|| 
|| [[Oberon (moon)|Oberon]] 
|| 1787
||1700s
||[[File:Voyager_2_picture_of_Oberon.jpg|50px]]
||
|-
|| [[File:Ceres symbol (fixed width).svg|x50px|alt=⚳]]
|| [[1 Ceres|Ceres]] 
|| 1801
|| 1867
|| [[Asteroid]] and [[dwarf planet]]
|| [[File:Ceres_-_RC3_-_Haulani_Crater_(22381131691)_(cropped).jpg|50px]]
|rowspan=7| 
The first asteroids to be discovered were accepted as planets in the Copernican system, since they directly orbited the Sun. By 1855 the number of known bodies in the [[asteroid belt]] had grown to 15, at which point astronomers started distinguishing these from the eight known major planets. The 1867 edition of ''[[Berliner Astronomisches Jahrbuch]]'' placed all the new bodies in the asteroid belt into a separate category as 'minor planets' or 'asteroids', by which point almost 100 asteroids had been observed.<ref>{{Cite web|url=http://www.usno.navy.mil/USNO/astronomical-applications/astronomical-information-center/minor-planets/|archive-url = https://web.archive.org/web/20120406222551/http://www.usno.navy.mil/USNO/astronomical-applications/astronomical-information-center/minor-planets/|archive-date = 2012-04-06|title = When did the asteroids become minor planets? – Naval Oceanography Portal}}</ref>
| rowspan=7|
<ref name=USNO-AAO-minorplanets>
{{cite web|url=http://aa.usno.navy.mil/faq/docs/minorplanets.php |title=When did the asteroids become minor planets? |author=James L. Hilton |date=18 April 2016 |work=Astronomical Applications Department |publisher=U.S. Naval Observatory |url-status=dead |archive-url=https://web.archive.org/web/20080324182332/http://aa.usno.navy.mil/faq/docs/minorplanets.php |archive-date=24 March 2008 }}
</ref><ref>{{Cite book|url=https://books.google.com/books?id=AbZqDwAAQBAJ&q=mercury+venus+earth+mars+ceres+pallas+juno+vesta+astraea+hebe+iris&pg=PA130|title = How to Speak Science: Gravity, Relativity, and Other Ideas That Were Crazy Until Proven Brilliant|isbn = 9781615194032|last1 = Benamran|first1 = Bruce|date =  2018| publisher=The Experiment }}</ref>
|-
|| [[File:Pallas symbol (fixed width).svg|x50px|alt=⚴]]
|| [[2 Pallas|Pallas]]
|| 1802
|| 1867 
|rowspan=6| [[Asteroid]]
|| [[File:Potw1749a_Pallas_crop.png|50px]]
|-
|| [[File:Juno symbol (fixed width).svg|x50px|alt=⚵]]
|| [[3 Juno|Juno]]
|| 1804
|| 1867
|| [[File:Juno from Hooker telescope.jpg|50px]]
|-
|| [[File:Vesta symbol (original, fixed width).svg|x50px]]
|| [[4 Vesta|Vesta]]
|| 1807
|| 1867 
|| [[File:Vesta_in_natural_color_(cropped).jpg|50px]]
|-
|| [[File:Astraea symbol (fixed width).svg|x50px]]
|| [[5 Astraea|Astraea]]
|| 1845
|| 1867 
||
|-
|| [[File:Hebe symbol (fixed width).svg|50px]]
|| [[6 Hebe|Hebe]]
|| 1847
|| 1867 
|| [[File:6hebe.png|50px]]
|-
|| [[File:Iris symbol (fixed width).svg|50px]]
|| [[7 Iris|Iris]]
|| 1847
|| 1867 
|| [[File:Iris asteroid eso.jpg|50px]]
|-
|| [[File:Chiron symbol (fixed width).svg|50px|⚷]]
|| [[2060 Chiron|Chiron]]
|| 1977 
|| 1980
|| {{sort|Centaur|[[Centaur (minor planet)|Centaur]]}}
||[[File:2060 Chiron Hubble.jpg|50x50px]]
|| The discovery of Chiron was hailed by the press and astrologers as that of a new planet. Astronomically, it was different from any other planets, asteroids and comets known at the time, and it was classified as unique at that time. Later it was called an [[asteroid]], and then was found to exhibit characteristics of a [[comet]], leading to multiple classifications. Later it was placed into its own category of [[Centaur (small Solar System body)|centaur]]s, and many other centaurs have been discovered subsequently.
|| 
<ref>
{{cite journal |title= The Discovery of Chiron: Some Reflections |author= Hodgson, Richard G. |journal= The Minor Planet Bulletin |volume= 5 |number= 3 |pages= 21–22 |date= March 1978 |bibcode= 1978MPBu....5...21H |publisher= IAU MPC }}
</ref><ref>
{{cite web |url= https://www.spiritualastrology.com/article15.html |title= Chiron and the Centaurs |date= 2004 |work= Emerald Visions |publisher= Mystic Visions Spiritual Astrology }}
</ref><ref>
{{cite book |title= Chiron: Rainbow Bridge Between the Inner and Outer Planets |author= Barbara Hand Clow |year= 1987 |isbn= 087542094X |publisher= Llewellyn }}
</ref>
<ref>
{{cite book |title= Chiron: The New Planet in Your Horoscope, The Key to Your Quest |author= Richard Nolle |isbn= 0866902368 |year= 1983 |publisher= American Federation of Astrologers }}
</ref><ref>
{{cite magazine |title= In Greenwich |magazine= Popular Mechanics |date= January 1982 |volume= 158 |number= 1 |page= 28 }}
</ref>
|-
|| [[File:Pluto monogram (fixed width).svg|50px|♇]]<br/>[[File:Pluto symbol (large orb, fixed width).svg|50px|⯓]]
|| [[Pluto]]
|| 1930
|| 2006 
|| [[Dwarf planet]]
|| [[File:Pluto_in_True_Color_-_High-Res.jpg|50px]]
|| Following its discovery in 1930, Pluto was considered the ninth planet. Numerous scientific discoveries in the 1990s and early 2000s placed doubt on this classification, and after the discovery of [[Eris (dwarf planet)|Eris]], which was thought to be larger than Pluto, the [[International Astronomical Union]] met to determine a definition of a planet. Like the asteroids before them, Pluto was grouped with Eris and similar bodies as members of a group of smaller objects designated as [[dwarf planets]].
|| 
<ref name=Space-2006-08-24>
{{cite news |url= http://www.space.com/2791-pluto-demoted-longer-planet-highly-controversial-definition.html |title= Pluto Demoted: No Longer a Planet in Highly Controversial Definition |date= 24 August 2006 |author= Robert Roy Britt |publisher= SPACE.com }} 
</ref><ref name=Space-MikeBrown/>
|-
||
|| [[Charon (moon)|Charon]]
|| 1978
|| 2006 
|| {{sort|Moon|[[Natural satellite|Moon]] of Pluto}}
|| [[File:Charon_in_True_Color_-_High-Res.jpg|50px]]
|| When discovered, Charon, the moon of Pluto, was found to be very large, leading to the declaration by many that the [[Pluto-Charon system]] was a [[double planet]] (binary planet). The 2006 IAU redefinition of planet excludes the possibility of double planets.
|| 
<ref name=Space-2006-08-24/><ref name=Space-MikeBrown/><ref name=Padua-PlutoCharon>
{{cite web |url= http://archive.oapd.inaf.it/E-MOSTRA/NEW/A2024PLU.HTM |title= Pluto and Charon |author= E. Mostra |work= Voyage in the Universe |date= 1998 |publisher= Astronomical Observatory of Padua }} 
</ref>
|-
||
||[[15760 Albion]]
||1992
||unknown
|rowspan=2|[[Trans-Neptunian object]]
||[[File:1992 QB1 crop.jpg|50x50px]]
|rowspan=2|When discovered, these bodies were briefly hailed as the tenth and eleventh planets by the press, but it was then decided that 15760 Albion was the prototype of [[Trans-Neptunian object|trans-Neptunian objects]] or [[cubewanos]].
||<ref>{{Cite journal|last1=Collander-Brown|first1=S.|last2=Maran|first2=M.|last3=Williams|first3=I. P.|date=2000-10-11|title=The effect on the Edgeworth-Kuiper Belt of a large distant tenth planet|journal=Monthly Notices of the Royal Astronomical Society|language=en|volume=318|issue=1|pages=101–108|doi=10.1046/j.1365-8711.2000.03640.x|bibcode=2000MNRAS.318..101C|issn=0035-8711|doi-access=free}}</ref><ref name="coote">{{Cite book|title=The earth|last=Coote, Roger. /|isbn=9781842399491|location=London|oclc=671197414|date= 2008|url-access=registration|url=https://archive.org/details/earth0000coot}}</ref>
|-
||
||[[(181708) 1993 FW]]
||1992
||unknown
||
||<ref name="coote"/>
|-
|| [[File:Eris symbol (fixed width).svg|50px|⯰]] 
|| [[Eris (dwarf planet)|Eris]]
|| 2005
|| 2006
|| [[Dwarf planet]]
|| [[File:Eris and dysnomia-cut.jpg|50px]]
|| The discovery of Eris, hailed worldwide by the press as the tenth planet, prompted the [[International Astronomical Union]] to meet and establish a new definition of planet. It was recategorised as a dwarf planet, together with Pluto and numerous other objects.
|| 
<ref name=Space-MikeBrown>
{{cite web |url= http://www.space.com/9563-man-killed-pluto-astronomer-mike-brown.html |title= The Man Who Killed Pluto: Q & A with Astronomer Mike Brown |author= Mike Wall |date= 19 November 2010 |publisher= Space.com }}
</ref><ref name=BBC-2005-07-30>
{{cite news |url= http://news.bbc.co.uk/2/hi/science/nature/4730061.stm |date= 30 July 2005 |title= Astronomers detect '10th planet' |author= David Whitehouse  |work= BBC News }} 
</ref>
|-
|}

==See also==
* [[List of gravitationally rounded objects of the Solar System]]
* [[List of possible dwarf planets]]
* [[List of hypothetical Solar System objects]]

==Notes==
{{Reflist|group=NB}}

==References==
{{reflist}}

{{Solar System}}
{{Exoplanet}}
{{Portal bar|Stars|Spaceflight|Outer space|Science}}
[[Category:Lists of planets|Former planets]]
[[Category:Lists of former entities|Planets]]