The timeline of discovery of Solar System planets and their natural satellites charts the progress of the discovery of new bodies over history. Each object is listed in chronological order of its discovery (multiple dates occur when the moments of imaging, observation, and publication differ), identified through its various designations (including temporary and permanent schemes), and the discoverer(s) listed.

Historically the naming of moons did not always match the times of their discovery. Traditionally, the discoverer enjoys the privilege of naming the new object; however, some neglected to do so (E. E. Barnard stated he would "defer any suggestions as to a name" [for Amalthea] "until a later paper"^[1] but never got around to picking one from the numerous suggestions he received) or actively declined (S. B. Nicholson stated "Many have asked what the new satellites [Lysithea and Carme] are to be named. They will be known only by the numbers X and XI, written in Roman numerals, and usually prefixed by the letter J to identify them with Jupiter."^[2]). The issue arose nearly as soon as planetary satellites were discovered: Galileo referred to the four main satellites of Jupiter using numbers while the names suggested by his rival Simon Marius gradually gained universal acceptance. The International Astronomical Union (IAU) eventually started officially approving names in the late 1970s. With the explosion of discoveries in the 21st century, new moons have once again started to be left unnamed even after their numbering, beginning with Jupiter LI and Jupiter LII in 2010.

In the following tables, planetary satellites are indicated in bold type (e.g. Moon) while planets and dwarf planets, which directly circle the Sun, are in italic type (e.g. Earth). The Sun itself is indicated in roman type. 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;
• p: for date of announcement or publication.

In a few cases, the date is uncertain and is then marked "(?)".

* Note: Moons marked by an asterisk (*) had complicated discoveries, such as being lost and rediscovered. Some of them thus appear multiple times in the list to clarify the situation.

Color legend

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

It is not known precisely how many objects in the Solar System are dwarf planets; the eight objects listed in the third column are the ones agreed on by most astronomers, corresponding to a threshold of about 900–1000 km diameter.

Designations

• Other designations are synonyms or periphrases sometimes encountered for the object.
• Permanent designations (of planetary satellites) are explained here.
• Temporary designations are explained here.

If a satellite is named, its name is bolded; if it is unnamed, but has a permanent designation, then its permanent designation is bolded; and if it has neither, then its temporary designation is bolded.

More information 17th century, Date ...

17th century
Date	Name	Image	Permanent designation	Discoverer(s) and notes
1610s
o: 7 January 1610 p: 13 March 1610	Ganymede		Jupiter III	Galileo[9][10] discovered the Galilean moons. These satellites were the first celestial objects that were confirmed to orbit an object other than the Sun or Earth. Galileo saw Io and Europa as a single point of light on 7 January 1610; they were seen as separate bodies the following night.[11]
	Callisto		Jupiter IV
o: 8 January 1610 p: 13 March 1610	Io		Jupiter I
	Europa		Jupiter II
1650s
o: 25 March 1655 p: 5 March 1656	Titan		Saturn VI Saturn II (1673–1684), Saturn IV (1686–1789)	Huygens[12] first "published" his discovery as an anagram, sent out on 13 June 1655; later published in pamphlet form as De Saturni luna Observatio Nova and in full in Systema Saturnium[13] (July 1659).
1670s
o: 25 October 1671 p: 1673	Iapetus		Saturn VIII Saturn III (1673–1684), Saturn V (1686–1789), Saturn VII (1789–1848)	Cassini[14]
o: 23 December 1672 p: 1673	Rhea		Saturn V Saturn I (1673–1684), Saturn III (1686–1789)
1680s
o: 21 March 1684 p: 22 April 1686	Tethys		Saturn III Saturn I (1686–1789)	Cassini[15] Together with his previous two discoveries, Cassini named these satellites Sidera Lodoicea. In his work Kosmotheôros[16] (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	Permanent designation	Discoverer(s) and notes

Close

The numbering of Saturn's moons was adjusted with each new discovery until 1848, in order to continue reflecting their order from their parent planet.

More information 18th century, Date ...

18th century
Date	Name	Image	Other/Permanent designation	Discoverer(s) and 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 to be a comet.[17]
: January 11, 1787 p: February 15, 1787	Titania		Uranus III Uranus I (1787–1797)	Herschel.[18][19] He later reported four more spurious satellites.[20]
	Oberon		Uranus IV Uranus II (1787–1797)
o: August 28, 1789[21] p: November 12, 1789	Enceladus		Saturn II	Herschel[22]
o: September 17, 1789 p: November 12, 1789	Mimas		Saturn I
Date	Name	Image	Other/Permanent designation	Discoverer(s) and notes

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The numbering of Titania and Oberon underwent some confusion, because in 1797, Herschel reported four more satellites of Uranus^[23] that turned out not to exist. Before any more Uranian moons were discovered, William Lassell sometimes adopted Herschel's numbers where Titania and Oberon are respectively Uranus II and IV,^[24] and sometimes called them respectively Uranus I and II.^[25] After he discovered Ariel and Umbriel in 1851, Lassell numbered the four real Uranian satellites then known outward from their parent planet as I (Ariel), II (Umbriel), III (Titania), and IV (Oberon), and this finally stuck.^[26]

More information 19th century, Date ...

19th century
Date	Name	Image	Other/Permanent designation	Discoverer(s) and 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.[27] The first formal publication was the September 1801 issue of the Monatliche Correspondenz.[28]
1840s
o: September 23, 1846 p: November 13, 1846	Neptune		13th Planet (1846)[lower-alpha 1] 8th Planet (1851)	Galle and Le Verrier[29][30]
o: October 10, 1846 p: November 13, 1846	Triton		Neptune I	Lassell[31]
o: September 16, 1848 p: October 7, 1848	Hyperion		Saturn VII	Bond, Bond,[32] Lassell[33]
1850s
o: October 24, 1851	Ariel		Uranus I	Lassell[26]
	Umbriel		Uranus II
1870s
o: August 12, 1877	Deimos		Mars II	Hall[34][35][36]
o: August 18, 1877	Phobos		Mars I
1890s
o: September 9, 1892 p: October 4, 1892	Amalthea		Jupiter V	Barnard[1][37]
i: August 16, 1898 o: March 17, 1899	Phoebe		Saturn IX	Pickering[38][39]
Date	Name	Image	Other/Permanent designation	Discoverer(s) and notes

Close

The discovery of Amalthea marks the first time the Roman numerals were not adjusted with the discovery of a new satellite; from then on they reflected order of discovery rather than distance from the parent planet.

• Timeline of Solar System astronomy
• Timeline of Solar System exploration
• Lists of astronomical objects
• Solar System