Timeline of discovery of Solar System planets and their moons

2008/9 Schools Wikipedia Selection. Related subjects: Space (Astronomy); The Planets

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.

Colour 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 Eris and satellite

Prehistory

Prehistory
Name	Image	Planet/Number Designation	References/Notes
Sun		Star	In the Ptolemaic system, the Earth was believed to be at the centre of the cosmos. Seven planets were placed in orbit around it in an order of increasing distance from the Earth, first 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 centre 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. 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. 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)	Cassini
o: December 23, 1672 p: 1673	Rhea		Saturn V Saturn I (1673–1684), Saturn III (1686–1789)	Cassini
1680s
o: March 21, 1684 p: April 22, 1686	Tethys		Saturn III Saturn I (1686–1789)	Cassini. 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."
o: March 21, 1684 p: April 22, 1686	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 comet
o: January 11, 1787 p: February 15, 1787	Titania		Uranus III	Herschel. He later reported four more spurious satellites.
o: January 11, 1787 p: February 15, 1787	Oberon		Uranus IV	Herschel. He later reported four more spurious satellites.
o: August 28, 1789 p: November 12, 1789	Enceladus		Saturn II	Herschel
o: September 17, 1789 p: November 12, 1789	Mimas		Saturn I	Herschel
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 Verrier
o: October 10, 1846 p: November 13, 1846	Triton		Neptune I	Lassell
o: September 16, 1848 p: October, 1848	Hyperion		Saturn VII	Bond, Bond, Lassell
1850s
o: October 24, 1851	Ariel		Uranus I	Lassell
o: October 24, 1851	Umbriel		Uranus II	Lassell
1870s
o: August 12, 1877	Deimos		Mars II	Hall
o: August 18, 1877	Phobos		Mars I	Hall
1890s
o: September 9, 1892 p: October 4, 1892	Amalthea		Jupiter V	Barnard
i: August 16, 1898 o: March 17, 1899	Phoebe		Saturn IX	Pickering
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	Perrine
i: January 2, 1905 p: February 27, 1905	Elara (Hera 1955-1975)		Jupiter VII	Perrine
i: January 27, 1908 o: February 28, 1908 p: March 1-6 1908	Pasiphaë (Poseidon 1955-1975)		Jupiter VIII	Melotte
1910s
i: July 21, 1914 p: September 17, 1914	Sinope (Hades 1955-1975)		Jupiter IX	Nicholson
1930s
i: January 23, 1930 o: February 18, 1930 p: March 13, 1930	Pluto		9th Planet (1930) Dwarf planet (2006)	Tombaugh
i: July 6, 1938 p: August 1938	Lysithea (Demeter 1955-1975)		Jupiter X	Nicholson
i: July 30, 1938 p: August 1938	Carme (Pan 1955-1975)		Jupiter XI	Nicholson
1940s
i: February 16, 1948 p: June 1949	Miranda		Uranus V	Kuiper
i: May 1, 1949 p: August 1949	Nereid		Neptune II	Kuiper
1950s
i: September 28, 1951 p: December 1951	Ananke (Adrastea 1955-1975)		Jupiter XII	Nicholson
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	Dollfus (Dollfus may have seen either Janus or Epimetheus)
i: December 18, 1966 p: January 6, 1967	Epimetheus*	S/1980 S 3		Saturn XI	Walker
1970s
i: September 11, 1974 p: September 20, 1974	Leda			Jupiter XIII	Kowal
i: September 30, 1975 p: October 3, 1975	Themisto*	S/1975 J 1		Jupiter XVIII	Kowal (Discovered and then lost)
i: April 13, 1978 o: June 22, 1978	Charon	S/1978 P 1		Pluto I	Christy
i: July 8, 1979 p: November 23, 1979	Adrastea	S/1979 J 1		Jupiter XV	Jewitt, Danielson / Voyager 2
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	(Confirmed by Voyager 1)
i: March 1, 1980 p: March 6, 1980	Helene	S/1980 S 6		Saturn XII	Laques, Lecacheux
i: April 8, 1980 p: April 10, 1980	Telesto	S/1980 S 13		Saturn XIII	Smith, Reitsema, Larson, Fountain, Voyager 1
i: March 5, 1979 p: April 28, 1980	Thebe	S/1979 J 2		Jupiter XIV	Synnott, Voyager 1
i: February 19, 1980 p: June 6, 1980	Janus*	S/1980 S 1		Saturn X	(Confirmed by Voyager 1)
i: March 13, 1980 p: July 31, 1980	Calypso	S/1980 S 25		Saturn XIV	Pascu, Seidelmann, Baum, Currie
i: March 4, 1979 p: August 26, 1980	Metis	S/1979 J 3		Jupiter XVI	Synnott, Voyager 1
o: October, 1980 p: October 31, 1980	Prometheus	S/1980 S 27		Saturn XVI	Collins, Voyager 1
o: October, 1980 p: October 31, 1980	Pandora	S/1980 S 26		Saturn XVII	Collins, Voyager 1
o: October, 1980 p: November 13, 1980	Atlas	S/1980 S 28		Saturn XV	Terrile, Voyager 1
i: May 24, 1981 p: 29 May 1981	Larissa*	S/1981 N 1 = S/1989 N 2		Neptune VII	Reitsema, Hubbard, Lebofsky, Tholen, Voyager 2
i: December 30, 1985 p: January 9, 1986	Puck	S/1985 U 1		Uranus XV	Synnott, Voyager 2
i: January 3, 1986 p: January 16, 1986	Juliet	S/1986 U 2		Uranus XI	Synnott, Voyager 2
i: January 3, 1986 p: January 16, 1986	Portia	S/1986 U 1		Uranus XII	Synnott, Voyager 2
i: January 9, 1986 p: January 16, 1986	Cressida	S/1986 U 3		Uranus IX	Synnott, Voyager 2
i: January 13, 1986 p: January 16, 1986	Desdemona	S/1986 U 6		Uranus X	Synnott, Voyager 2
	Rosalind	S/1986 U 4		Uranus XIII	Synnott, Voyager 2
	Belinda	S/1986 U 5		Uranus XIV	Synnott, Voyager 2
i: January 20, 1986 p: January 27, 1986	Cordelia	S/1986 U 7		Uranus VI	Terrile, Voyager 2
i: January 20, 1986 p: January 27, 1986	Ophelia	S/1986 U 8		Uranus VII	Terrile, Voyager 2
i: January 23, 1986 p: January 27, 1986	Bianca	S/1986 U 9		Uranus VIII	Smith, Voyager 2
i: June 16, 1989 p: July 7, 1989	Proteus	S/1989 N 1		Neptune VIII	Synnott, Voyager 2
i: July 28, 1989 p: August 2, 1989	Despina	S/1989 N 3		Neptune V	Synnott, Voyager 2
i: July 28, 1989 p: August 2, 1989	Galatea	S/1989 N 4		Neptune VI	Synnott, Voyager 2
i: September 18, 1989 p: September 29, 1989	Thalassa	S/1989 N 5		Neptune IV	Terrile, Voyager 2
i: September 18, 1989 p: September 29, 1989	Naiad	S/1989 N 6		Neptune III	Terrile, Voyager 2
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 2
i: August 23, 1981 p: April 14, 1995	Pallene* (see below)	S/1981 S 14			Gordon, Murray and Beurle
i: September 6, 1997 p: October 31, 1997	Caliban	S/1997 U 1		Uranus XVI	Gladman, Nicholson, Burns, Kavelaars
i: September 6, 1997 p: October 31, 1997	Sycorax	S/1997 U 2		Uranus XVII	Gladman, Nicholson, Burns, Kavelaars
i: January 18, 1986 p: May 18, 1999	Perdita*	S/1986 U 10		Uranus XXV	Karkoschka, Voyager 2
i: July 18, 1999 p: July 27, 1999	Setebos	S/1999 U 1		Uranus XIX	Kavelaars, Gladman, Holman, Petit, Scholl
i: July 18, 1999 p: July 27, 1999	Stephano	S/1999 U 2		Uranus XX	Gladman, Holman, Kavelaars, Petit, Scholl
i: July 18, 1999 p: September 4, 1999	Prospero	S/1999 U 3		Uranus XVIII	Holman, Kavelaars, Gladman, Petit, Scholl
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, Gehrels
i: August 7, 2000 p: October 25, 2000	Ymir	S/2000 S 1		Saturn XIX	Gladman
i: August 7, 2000 p: October 25, 2000	Paaliaq	S/2000 S 2		Saturn XX	Gladman
i: September 23, 2000 p: October 25, 2000	Siarnaq	S/2000 S 3		Saturn XXIX	Gladman, Kavelaars
i: September 23, 2000 p: October 25, 2000	Tarvos	S/2000 S 4		Saturn XXI	Kave