Naming of natural satellites

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The naming of natural satellites has been the responsibility of the IAU's committee for Planetary System Nomenclature since 1973. That committee is known today as the Working Group for Planetary System Nomenclature (WGPSN).

Prior to its formation, the names of satellites have had varying histories. The choice of names is often determined by a satellite's discoverer; however, historically some satellites were not given names for many decades or even centuries after their discovery.

1 Naming of satellites by planet
- 1.1 Mars
- 1.2 Jupiter
- 1.3 Saturn
- 1.4 Uranus
- 1.5 Neptune
- 1.6 Pluto
- 1.7 Eris
2 Roman numeral designations
- 2.1 Table of natural satellites by Roman numeral
3 Recent developments
4 See also
5 References

[edit] Naming of satellites by planet

[edit] Mars

The moons of Mars (Phobos and Deimos) were named by Asaph Hall in 1878, soon after he discovered them.

[edit] Jupiter

Main article: Jupiter's natural satellites

The Galilean moons of Jupiter (Io, Europa, Ganymede and Callisto) were named by Simon Marius soon after their discovery in 1610. However, by the late 19th century these names had fallen out of favor, and for a long time (until the mid 20th century) it was most common to refer to them in the astronomical literature simply as "Jupiter I", "Jupiter II", etc., or as "the first satellite of Jupiter", "Jupiter's second satellite", etc.

The moons of Jupiter discovered between 1904 and 1951 were not named until 1975, being known until then simply by their Roman numeral designations (Jupiter VI through Jupiter XII). The moon Amalthea (Jupiter V), discovered in 1892, was unofficially named but its name was also not made official until 1975. Since the names of the Galilean satellites themselves had fallen out of favor, it is perhaps not unusual that the discoverers of the new smaller satellites did not see fit to name them either.

Most likely Charles Kowal's discovery of Leda (Jupiter XIII) in 1974 finally prompted the International Astronomical Union to establish a formal nomenclature process. Under the new process, informal names given to seven of the satellites were abandoned in favor of new names. [1]

Number	Unofficial name (pre-1975)	Official name (since 1975)
Jupiter V	Amalthea	Amalthea
Jupiter VI	Hestia	Himalia
Jupiter VII	Hera	Elara
Jupiter VIII	Poseidon	Pasiphaë
Jupiter IX	Hades	Sinope
Jupiter X	Demeter	Lysithea
Jupiter XI	Pan	Carme
Jupiter XII	Adrastea	Ananke

Current practice is that newly discovered moons of Jupiter must be named after lovers of the mythological Jupiter (Zeus). A convention has also emerged among the outer moons, whereby prograde moons are given names ending in 'a' or 'o', and retrograde moons receive names ending in 'e'. In 2004, with new Jovian moons continuing to be discovered, these rules were found to be excessively restrictive, and so the IAU agreed to permit moons to be named after Zeus's descendants as well.

[edit] Saturn

Main article: Saturn's natural satellites

The seven known moons (at the time) of Saturn were named in 1847 by John Herschel. Herschel's system was to name Saturn's moons after the mythological Greek Titans. Until then, Titan was known as the "Huygenian (or Huyghenian) satellite of Saturn" and the other moons had Roman numeral designations in order of their distance from Saturn. Subsequent discoverers of Saturnian moons followed Herschel's scheme: Hyperion was discovered soon after in 1848; the ninth moon, Phoebe was named by its discoverer in 1899 soon after its discovery; and the name of Janus was suggested by its discoverer, Audouin Dollfus.

Current IAU practice for newly discovered inner moons is to continue with Herschel's system, naming them after Titans or their descendants. However, the increasing number of moons that were being discovered in the 21st century caused the IAU to draw up a new scheme for the outer moons, which are named after giants in the mythologies of other cultures. Since the outer moons fall naturally into three groups, one group is named after Norse giants, one after Gallic giants, and one after Inuit giants. The only moon that fails to fit this scheme is the Greek-named Phoebe, which is in the Norse group.

[edit] Uranus

Main article: Uranus' natural satellites

The first two Uranian moons, discovered in 1787, did not receive names until 1852, a year after two more moons had been discovered. The responsibility for naming was taken by John Herschel, son of the discoverer of Uranus. Herschel broke with tradition: instead of assigning names from Greek mythology, he named the moons after magical spirits in English literature: Oberon and Titania from William Shakespeare's A Midsummer Night's Dream, and Ariel and Umbriel from Alexander Pope's The Rape of the Lock.

Subsequent naming choices have accorded with Herschel's choices. In 1949, the fifth moon, Miranda, was named by its discoverer after a character in Shakespeare's The Tempest. Current IAU practice is to name moons after characters from Shakespeare's plays and The Rape of the Lock (although the names from Shakespeare far outnumber those from Pope). At first, the outermost moons were all named after characters from one play, The Tempest; but with Margaret being named from Much Ado About Nothing that trend has ended.

[edit] Neptune

Main article: Neptune's natural satellites

The one known moon (at the time) of Neptune was not named for many decades. Although the name Triton was suggested in 1880, it did not come into general use until the mid 20th-century. In the astronomical literature it was simply referred to as "the satellite of Neptune". Later, the second known moon, Nereid, was named by its discoverer in 1949 soon after its discovery.

Current IAU practice for newly discovered Neptunian moons is to accord with these first two choices by naming them after Greek sea deities.

[edit] Pluto

Main article: Pluto's natural satellites

The name of Pluto's moon Charon was suggested by James W. Christy, its discoverer, soon after its discovery.

As of June 22, 2006, the other two moons are named Hydra and Nix.

[edit] Eris

The name of Eris's moon Dysnomia was suggested by its discoverer Michael E. Brown, who also suggested the name of the dwarf planet. The names were accepted by the IAU on 14 September 2006.

[edit] Roman numeral designations

The Roman numbering system for satellites arose with the very first discovery of natural satellites other than Earth's Moon: Galileo referred to the Galilean moons as I through IV (counting from Jupiter outward), in part to spite his rival Simon Marius, who had proposed the names now adopted. Similar numbering schemes naturally arose with the discovery of moons around Saturn, Uranus, and Mars. The numbers initially designated the moons in orbital sequence, and were re-numbered after each new discovery; for instance, before the discovery of Mimas and Enceladus in 1789, Tethys was Saturn I, Dione Saturn II, etc.^[1], but after the new moons were discovered, Mimas became Saturn I, Enceladus Saturn II, Tethys Saturn III and Dione Saturn IV.

After the mid-to-late nineteenth century, however, the numeration became fixed, and later discoveries failed to conform with the orbital sequence scheme. Amalthea, discovered in 1892, was labelled "Jupiter V" although it orbits closer to Jupiter than does Io (Jupiter I). The unstated convention then became, at the close of the 19th century, that the numbers more or less reflected the order of discovery, except for prior historical exceptions (see the Timeline of discovery of Solar System planets and their natural satellites); though if a large number of satellites were discovered in a short span of time, the group could be numbered in orbital sequence, or according to other principles than strictly by order of discovery. The convention has been extended to natural satellites of minor planets, such as (87) Sylvia I Romulus.

Roman numerals are usually not assigned to satelllites until they are named, so many satellites that have been discovered but only have provisional designations do not have Roman numerals assigned to them. Since the International Astronomical Union began assigning names to all satellites in 1975, the use of Roman numeral designations has diminished, and some are very rarely used; Phobos and Deimos are rarely referred to as Mars I and Mars II, and the Moon is never referred to as "Earth I".

[edit] Table of natural satellites by Roman numeral

(with year of discovery and actual order of distance)

Roman numeral	Mars	Jupiter		Saturn		Uranus		Neptune		Pluto
I	Phobos 1877	Io 1610	5	Mimas 1789	8	Ariel 1851	15	Triton 1846	7	Charon 1978
II	Deimos 1877	Europa 1610	6	Enceladus 1789	11	Umbriel 1851	16	Nereid 1949	8	Nix 2005
III		Ganymede 1610	7	Tethys 1684	12	Titania 1787	17	Naiad 1989	1	Hydra 2005
IV		Callisto 1610	8	Dione 1684	15	Oberon 1787	18	Thalassa 1989	2
V		Amalthea 1892	3	Rhea 1672	18	Miranda 1948	14	Despina 1989	3
VI		Himalia 1904	11	Titan 1655	19	Cordelia 1986	1	Galatea 1989	4
VII		Elara 1905	13	Hyperion 1848	20	Ophelia 1986	2	Larissa 1989	5
VIII		Pasiphae 1908	52	Iapetus 1671	21	Bianca 1986	3	Proteus 1989	6
IX		Sinope 1914	58	Phoebe 1899	24	Cressida 1986	4
X		Lysithea 1938	12	Janus 1980	7	Desdemona 1986	5	Psamathe 2003	12
XI		Carme 1938	45	Epimetheus 1980	6	Juliet 1986	6
XII		Ananke 1951	31	Helene 1980	15a	Portia 1986	7
XIII		Leda 1974	10	Telesto 1980	12a	Rosalind 1986	8
XIV		Thebe 1979	4	Calypso 1980	12b	Belinda 1986	10
XV		Adrastea 1979	2	Atlas 1980	3	Puck 1985	12
XVI		Metis 1979	1	Prometheus 1980	4	Caliban 1997	20
XVII		Callirrhoe 1999	46	Pandora 1980	5	Sycorax 1997	23
XVIII		Themisto 2000	9	Pan 1990	1	Prospero 1999	25
XIX		Megaclite 2001	62	Ymir 2000	54	Setebos 1999	26
XX		Taygete 2001	35	Paaliaq 2000	25	Stephano 1999	21
XXI		Chaldene 2001	37	Tarvos 2000	36	Trinculo 2002	22
XXII		Harpalyke 2000	27	Ijiraq 2000	23	Francisco 2003	19
XXIII		Kalyke 2001	44	Suttungr 2000	42	Margaret 2003	24
XXIV		Iocaste 2001	24	Kiviuq 2000	22	Ferdinand 2003	27
XXV		Erinome 2001	41	Mundilfari 2000	37	Perdita 2003	11
XXVI		Isonoe 2001	55	Albiorix 2000	27	Mab 2003	13
XXVII		Praxidike 2001	26	Skathi 2000	26	Cupid 2003	9
XXVIII		Autonoe 2002	60	Erriapo 2000	29
XXIX		Thyone 2002	30	Siarnaq 2000	31
XXX		Hermippe 2002	29	Thrymr 2000	46
XXXI		Aitne 2002	33	Narvi 2003	41
XXXII		Eurydome 2002	47	Methone 2004	9
XXXIII		Euanthe 2002	21	Pallene 2004	10
XXXIV		Euporie 2002	17	Polydeuces 2004	15b
XXXV		Orthosie 2002	23	Daphnis 2005	2
XXXVI		Sponde 2002	59
XXXVII		Kale 2002	34
XXXVIII		Pasithee 2002	48
XXXIX		Hegemone 2003	53
XL		Mneme 2003	28
XLI		Aoede 2003	42
XLII		Thelxinoe 2004	20
XLIII		Arche 2002	54
XLIV		Kallichore 2003	43
XLV		Helike 2003	22
XLVI		Carpo 2003	15
XLVII		Eukelade 2003	50
XLVIII		Cyllene 2003	49

[edit] Recent developments

As of the IAU General Assembly in July 2004 [2], the WGPSN:

named 34 satellites of Jupiter and Saturn and one Uranus satellite, bringing the total number of known planetary satellites to 101, with over two dozen more awaiting recovery and naming;
suggested it may become advisable to not name small satellites (current CCD technology makes it possible to discover satellites as small as 1 km);
allowed Jovian satellites to be named for Zeus' descendants in addition to his lovers and favorites which were the previous source of names;
allowed satellites of Saturn to have names of giants and monsters in mythologies other than the Greco-Roman, including (so far) Gallic, Inuit and Norse.