Timeline of discovery of Solar System planets and their natural satellites.html



This timeline of discovery of Solar System planets and their natural satellites charts the progress of the discovery of new bodies over history.

Historically the naming of natural satellites did not always match the times of their discovery.

In the following tables, planetary satellites are indicated in bold type (e.g. Moon) while planets, major or minor, which directly circle the Sun are in italic type (e.g. Earth). The tables are sorted by publication/announcement date. Dates are annotated with the following symbols:

• i: for date of first imaging (photography, etc.);
• o: for date of first human visual observation, either through telescope or on photographic plate (the true "discovery" moment);
• p: for date of announcement or publication.

*Note: Marked moons had complicated discoveries. Several moons took several years to be confirmed, and in several cases were actually lost and rediscovered. Others were found in Voyager photographs years after they were taken.

Color legend

The planets and their natural satellites are marked in the following colors:

Planets

     Mercury      Venus      Earth and satellite      Mars and satellites      Jupiter and satellites      Saturn and satellites      Uranus and satellites      Neptune and satellites

Dwarf planets

     Ceres      Pluto and satellites      Haumea and satellites      Makemake      Eris and satellite

Prehistory

Prehistory
Name	Image	Planet/Number Designation	References/Notes
Sun		Star	In Ptolemy's geocentric model, the Earth was believed to be at the center of the cosmos. Seven planets were placed in orbit around it in an order of increasing distance from the Earth, as established by the Greek Stoics: the Moon, Mercury, Venus, the Sun, Mars, Jupiter and Saturn. This list included two objects, the Sun and the Moon, which are no longer considered to be planets; it also excluded the Earth.
Mercury		1st Planet	In Nicolaus Copernicus' heliocentric system (De Revolutionibus Orbium Coelestium, 1543) the Earth came to be considered a planet revolving with the other planets around the Sun, in the following order of distance from the Sun: Mercury, Venus, Earth, Mars, Jupiter, and Saturn. The Sun, now situated near the center of revolution, was no longer considered a planet.
Venus		2nd Planet
Earth		3rd Planet
Mars		4th Planet
Jupiter		5th Planet
Saturn		6th Planet
Moon		Earth I	In the Copernican system, the Moon was considered to be no longer a planet but a natural satellite of the Earth, and was the only body in that system whose revolution was not centered on the Sun.

17th century

17th century
Date	Name	Image	Planet/Number Designation	References/Notes
1610s
o: January 7, 1610 p: March 13, 1610	Callisto		Jupiter IV	Galileo.1 The Galilean moons. Note: One of the moons may have been recorded by the Chinese astronomer Gan De in 364 BC. The Galilean satellites were the first celestial objects that were confirmed to orbit an object other than the Earth.
	Io		Jupiter I
	Europa		Jupiter II
o: January 11, 1610 p: March 13, 1610	Ganymede		Jupiter III
1650s
o: March 25, 1655 p: March 5, 1656	Titan		Saturn VI Saturn II (1673–1684), Saturn IV (1686–1789)	Huygens.2 He first "published" his discovery as an anagram, sent out on June 13, 1655; later published in pamphlet form as De Saturni luna Observatio Nova and in full in Systema Saturnium (July 1659).
1670s
o: October 25, 1671 p: 1673	Iapetus		Saturn VIII Saturn III (1673–1684), Saturn V (1686–1789), Saturn VII (1789–1848)	Cassini3
o: December 23, 1672 p: 1673	Rhea		Saturn V Saturn I (1673–1684), Saturn III (1686–1789)
1680s
o: March 21, 1684 p: April 22, 1686	Tethys		Saturn III Saturn I (1686–1789)	Cassini.4 Together with his previous two discoveries, Cassini named these satellites Sidera Lodoicea. In his work Kosmotheôros (published posthumously in 1698), Christiaan Huygens relates "Jupiter you see has his four, and Saturn his five Moons about him, all plac’d in their Orbits."
	Dione		Saturn IV Saturn II (1686–1789)
Date	Name	Image	Planet/Number Designation	References/Notes

18th century

18th century
Date	Name	Image	Planet/Number Designation	References/Notes
1780s
o: March 13, 1781 p: April 26, 1781	Uranus		7th Planet	Herschel first reported the discovery of Uranus on April 26, 1781, initially believing it a comet5
o: January 11, 1787 p: February 15, 1787	Titania		Uranus III	Herschel.67 He later reported four more spurious satellites.8
	Oberon		Uranus IV
o: August 28, 17899 p: November 12, 1789	Enceladus		Saturn II	Herschel10
o: September 17, 1789 p: November 12, 1789	Mimas		Saturn I
Date	Name	Image	Planet/Number Designation	References/Notes

19th century

19th century
Date	Name	Image	Planet/Number Designation	References/Notes
1800s
o: January 1, 1801 p: January 24, 1801	Ceres		8th Planet (1801) Asteroid (1851) Dwarf planet (2006)	Giuseppe Piazzi. He first announced his discovery on January 24, 1801, in letters to fellow astronomers. The first formal publication was the September 1801 issue of the Monatliche Correspondenz.
1840s
o: September 23, 1846 p: November 13, 1846	Neptune		13th Planet (1846) 8th Planet (1851)	Galle and Le Verrier1112
o: October 10, 1846 p: November 13, 1846	Triton		Neptune I	Lassell13
o: September 16, 1848 p: October, 1848	Hyperion		Saturn VII	Bond, Bond,14 Lassell15
1850s
o: October 24, 1851	Ariel		Uranus I	Lassell16
	Umbriel		Uranus II
1870s
o: August 12, 1877	Deimos		Mars II	Hall171819
o: August 18, 1877	Phobos		Mars I
1890s
o: September 9, 1892 p: October 4, 1892	Amalthea		Jupiter V	Barnard20
i: August 16, 1898 o: March 17, 1899	Phoebe		Saturn IX	Pickering2122
Date	Name	Image	Planet/Number Designation	References/Notes

Early 20th century

Early 20th century
Date	Name	Image	Planet/Number Designation	References/Notes
1900s
i: December 3, 1904 p: January 6, 1905	Himalia (Hestia 1955–1975)		Jupiter VI	Perrine2324252627
i: January 2, 1905 p: February 27, 1905	Elara (Hera 1955–1975)		Jupiter VII	Perrine282927
i: January 27, 1908 o: February 28, 1908 p: March 1–6, 1908	Pasiphaë (Poseidon 1955–1975)		Jupiter VIII	Melotte3031
1910s
i: July 21, 1914 p: September 17, 1914	Sinope (Hades 1955–1975)		Jupiter IX	Nicholson32
1930s
i: January 23, 1930 o: February 18, 1930 p: March 13, 1930	Pluto		9th Planet (1930) Dwarf planet (2006)	Tombaugh33
i: July 6, 1938 p: August 1938	Lysithea (Demeter 1955–1975)		Jupiter X	Nicholson34
i: July 30, 1938 p: August 1938	Carme (Pan 1955–1975)		Jupiter XI	Nicholson34
1940s
i: February 16, 1948 p: June 1949	Miranda		Uranus V	Kuiper35
i: May 1, 1949 p: August 1949	Nereid		Neptune II	Kuiper3637
1950s
i: September 28, 1951 p: December 1951	Ananke (Adrastea 1955–1975)		Jupiter XII	Nicholson38
Date	Name	Image	Planet/Number Designation	References/Notes

Later 20th century

Later 20th century
Date	Name	Designation	Image	Planet/Number Designation	References/Notes
1960s
i: December 15, 1966 p: January 3, 1967	Janus*	S/1966 S 2		Saturn X	Dollfus394041424344 (Dollfus may have seen either Janus or Epimetheus)
i: December 18, 1966 p: January 6, 1967	Epimetheus*	S/1980 S 3		Saturn XI	Walker45
1970s
i: September 11, 1974 p: September 20, 1974	Leda			Jupiter XIII	Kowal46474849
i: September 30, 1975 p: October 3, 1975	Themisto*	S/1975 J 1		Jupiter XVIII	Kowal505152 (Discovered and then lost)
i: April 13, 1978 o: June 22, 1978	Charon	S/1978 P 1		Pluto I	Christy5354
i: July 8, 1979 p: November 23, 1979	Adrastea	S/1979 J 1		Jupiter XV	Jewitt, Danielson / Voyager 2554256575859
1980s
Date	Name	Designation	Image	Planet/Number Designation	References/Notes
i: February 26, 1980 p: March 6, 1980	Epimetheus*	S/1980 S 3		Saturn XI	6061624463 (Confirmed by Voyager 1)
i: March 1, 1980 p: March 6, 1980	Helene	S/1980 S 6		Saturn XII	Laques, Lecacheux60616263
i: April 8, 1980 p: April 10, 1980	Telesto	S/1980 S 13		Saturn XIII	Smith, Reitsema, Larson, Fountain, Voyager 16463
i: March 5, 1979 p: April 28, 1980	Thebe	S/1979 J 2		Jupiter XIV	Synnott, Voyager 15657
i: February 19, 1980 p: June 6, 1980	Janus*	S/1980 S 1		Saturn X	4261624463 (Confirmed by Voyager 1)
i: March 13, 1980 p: July 31, 1980	Calypso	S/1980 S 25		Saturn XIV	Pascu, Seidelmann, Baum, Currie6263
i:March 4, 1979 p: August 26, 1980	Metis	S/1979 J 3		Jupiter XVI	Synnott, Voyager 157
o: October, 1980 p: October 31, 1980	Prometheus	S/1980 S 27		Saturn XVI	Collins, Voyager 165
	Pandora	S/1980 S 26		Saturn XVII	Collins, Voyager 165
o: October, 1980 p: November 13, 1980	Atlas	S/1980 S 28		Saturn XV	Terrile, Voyager 166
i: May 24, 1981 p: May 29, 1981	Larissa*	S/1981 N 1 = S/1989 N 2		Neptune VII	Reitsema, Hubbard, Lebofsky, Tholen, Voyager 26768
i: December 30, 1985 p: January 9, 1986	Puck	S/1985 U 1		Uranus XV	Synnott, Voyager 269
i: January 3, 1986 p: January 16, 1986	Juliet	S/1986 U 2		Uranus XI	Synnott, Voyager 27071
	Portia	S/1986 U 1		Uranus XII	Synnott, Voyager 27071
i: January 9, 1986 p: January 16, 1986	Cressida	S/1986 U 3		Uranus IX	Synnott, Voyager 27071
i: January 13, 1986 p: January 16, 1986	Desdemona	S/1986 U 6		Uranus X	Synnott, Voyager 27071
	Rosalind	S/1986 U 4		Uranus XIII	Synnott, Voyager 27071
	Belinda	S/1986 U 5		Uranus XIV	Synnott, Voyager 27071
i: January 20, 1986 p: January 27, 1986	Cordelia	S/1986 U 7		Uranus VI	Terrile, Voyager 272
	Ophelia	S/1986 U 8		Uranus VII	Terrile, Voyager 272
i: January 23, 1986 p: January 27, 1986	Bianca	S/1986 U 9		Uranus VIII	Smith, Voyager 272
i: June 16, 1989 p: July 7, 1989	Proteus	S/1989 N 1		Neptune VIII	Synnott, Voyager 273
i: July 28, 1989 p: August 2, 1989	Despina	S/1989 N 3		Neptune V	Synnott, Voyager 268
	Galatea	S/1989 N 4		Neptune VI	Synnott, Voyager 268
i: September 18, 1989 p: September 29, 1989	Thalassa	S/1989 N 5		Neptune IV	Terrile, Voyager 274
	Naiad	S/1989 N 6		Neptune III	Terrile, Voyager 274
1990s
Date	Name	Designation	Image	Planet/Number Designation	References/Notes
i: August 22, 1981 p: July 16, 1990	Pan*	S/1981 S 13		Saturn XVIII	Showalter, Voyager 275
i: August 23, 1981 p: April 14, 1995	Pallene* (see below)	S/1981 S 14			Gordon, Murray and Beurle7677
i: September 6, 1997 p: October 31, 1997	Caliban	S/1997 U 1		Uranus XVI	Gladman, Nicholson, Burns, Kavelaars78
	Sycorax	S/1997 U 2		Uranus XVII	Gladman, Nicholson, Burns, Kavelaars78
i: January 18, 1986 p: May 18, 1999	Perdita*	S/1986 U 10		Uranus XXV	Karkoschka, Voyager 279
i: July 18, 1999 p: July 27, 1999	Setebos	S/1999 U 1		Uranus XIX	Kavelaars, Gladman, Holman, Petit, Scholl80
	Stephano	S/1999 U 2		Uranus XX	Gladman, Holman, Kavelaars, Petit, Scholl80
i: July 18, 1999 p: September 4, 1999	Prospero	S/1999 U 3		Uranus XVIII	Holman, Kavelaars, Gladman, Petit, Scholl81
2000s
Date	Name	Designation	Image	Planet/Number Designation	References/Notes
i: October 6, 1999 p: July 20, 2000	Callirrhoe	S/1999 J 1		Jupiter XVII	Scotti, Spahr, McMillan, Larsen, Montani, Gleason, Gehrels8283
i: August 7, 2000 p: October 25, 2000	Ymir	S/2000 S 1		Saturn XIX	Gladman8485
	Paaliaq	S/2000 S 2		Saturn XX	Gladman8485
i: September 23, 2000 p: October 25, 2000	Siarnaq	S/2000 S 3		Saturn XXIX	Gladman, Kavelaars8687
	Tarvos	S/2000 S 4		Saturn XXI	Kavelaars, Gladman8687
i: August 7, 2000 p: November 18, 2000	Kiviuq	S/2000 S 5		Saturn XXIV	Gladman8887
i: September 23, 2000 p: November 18, 2000	Ijiraq	S/2000 S 6		Saturn XXII	Kavelaars, Gladman8887
i: November 21, 2000 p: November 25, 2000	Themisto*	S/2000 J 1		Jupiter XVIII	Sheppard, Jewitt, Fernández, Magnier (Rediscovered)8959
i: September 23, 2000 p: December 7, 2000	Thrymr	S/2000 S 7		Saturn XXX	Gladman, Kavelaars9085
	Skathi	S/2000 S 8		Saturn XXVII	Kavelaars, Gladman9085
	Mundilfari	S/2000 S 9		Saturn XXV	Gladman, Kavelaars9085
	Erriapus	S/2000 S 10		Saturn XXVIII	Kavelaars, Gladman9187
i: November 9, 2000 p: December 19, 2000	Albiorix	S/2000 S 11		Saturn XXVI	Holman, Spahr9293
i: September 23, 2000 p: December 22, 2000	Suttungr	S/2000 S 12		Saturn XXIII	Gladman, Kavelaars9495
Date	Name	Designation	Image	Planet/Number Designation	References/Notes

21st century