Pasiphae group

Moons of Jupiter

Jupiter has 62 confirmed moons, giving it the largest retinue of moons with "reasonably secure" orbits of any planet in the Solar System. The most massive of them, the four Galilean moons, were discovered in 1610 and were the first objects found to orbit a body that was neither Earth nor the Sun. From the end of the 19th century, dozens of much smaller Jovian moons have been discovered and have received the names of lovers, conquests, or daughters of the Roman god Jupiter, or his Greek equivalent, Zeus.

Eight of Jupiter's moons are regular satellites, with prograde and nearly circular orbits that are not greatly inclined with respect to Jupiter's equatorial plane. The Galilean satellites are spheroidal in shape, and so would be considered dwarf planets if they were in direct orbit about the Sun. The other four regular satellites are much smaller and closer to Jupiter; these serve as sources of the dust that makes up Jupiter's rings.

Jupiter's other 54 or 55 moons are tiny irregular satellites, whose prograde and retrograde orbits are much farther from Jupiter and have high inclinations and eccentricities. These moons were likely captured by Jupiter from solar orbits. There are 13 recently-discovered irregular satellites that have not yet been named, plus a 14th whose orbit has not yet been established; if it is, the number of secured moons will rise to 63.

The moons' physical and orbital characteristics vary widely. Ganymede is the largest object in the Solar System outside the Sun and the eight planets, but some moons are barely one km (half a mile) in diameter. Even Europa, the smallest of the Galileans, is five thousand times more massive than all the non-Galilean moons combined. Orbital shapes range from nearly perfectly circular to highly eccentric and inclined, and many revolve in the direction opposite to Jupiter's spin (retrograde motion). Orbital periods range from seven hours (taking less time than Jupiter does to spin around its axis), to some 3000 times more (almost three Earth years).

Discovery

The first claimed observation of one of Jupiter's moons is that of the Chinese astronomer Gan De around 364 BC. However, the first certain observations of Jupiter's satellites were those of Galileo Galilei in 1609. By March 1610, he had sighted the four massive Galilean moons with his 30x magnitude telescope: Ganymede, Callisto, Io, and Europa. No additional satellites were discovered until E.E. Barnard observed Amalthea in 1892. With the aid of telescopic photography, further discoveries followed quickly over the course of the twentieth century. Himalia was discovered in 1904, Elara in 1905, Pasiphaë in 1908, Sinope in 1914, Lysithea and Carme in 1938, Ananke in 1951. and Leda in 1974. By the time Voyager space probes reached Jupiter around 1979, 13 moons had been discovered, while Themisto was observed in 1975, but due to insufficient initial observation data, it was lost until 2000. The Voyager missions discovered an additional three inner moons in 1979: Metis, Adrastea, and Thebe.

For two decades no additional moons were discovered; but between October 1999 and February 2003, researchers using sensitive ground-based detectors found another 32 moons, most of which were discovered by a team lead by Scott S. Sheppard and David C. Jewitt. These are tiny moons, in long, eccentric, generally retrograde orbits, and average of in diameter, with the largest being just across. All of these moons are thought to be captured asteroidal or perhaps cometary bodies, possibly fragmented into several pieces, but very little is actually known about them. A number of 14 additional moons were discovered since then, but not yet confirmed, bringing the total number of observed moons of Jupiter at 63. As of 2008, this is the most of any planet in the Solar System, but additional undiscovered, tiny moons may exist.

Naming

The Galilean moons of Jupiter (Io, Europa, Ganymede and Callisto) were named by Simon Marius soon after their discovery in 1610. However, until the 20th century these fell out of favor, and instead they were referred to in the astronomical literature simply as "Jupiter I", "Jupiter II", etc., or as "the first satellite of Jupiter", "Jupiter's second satellite", an so on. The names Io, Europa, Ganymede, and Callisto became popular in the 20th century, while the rest of the moons, usually numbered in Roman numerals V (5) through XII (12), remained unnamed. By a popular though unofficial convention, Jupiter V, discovered in 1892, was given the name Amalthea, first used by the French astronomer Camille Flammarion.

The other moons, in the majority of astronomical literature, were simply labeled by their Roman numeral (i.e. Jupiter IX) until the 1970s. In 1975, the International Astronomical Union's (IAU) "Task Group for Outer Solar System Nomenclature" granted names to satellites V–XIII, and provided for a formal naming process for future satellites to be discovered. The practice was to name that newly discovered moons of Jupiter after lovers and favorites of the god Jupiter (Zeus), and since 2004, after their descendants also. All of Jupiter's satellites from XXXIV (Euporie) are named after daughters of Jupiter or Zeus.

Some asteroids share the same names as moons of Jupiter: 9 Metis, 38 Leda, 52 Europa, 85 Io, 113 Amalthea, 239 Adrastea. Two more asteroids previously shared the names of Jovian moons until spelling differences were made permanent by the IAU: Ganymede and asteroid 1036 Ganymed; and Callisto and asteroid 204 Kallisto.

Groups

Regular satellites

These are split into two groups:

*Inner satellites or Amalthea group — they orbit very close to Jupiter: Metis, Adrastea, Amalthea, and Thebe. The innermost two orbit in less than a Jovian day, while the latter two are the fifth, respectively the seventh largest moons in the system. Observations suggest that at least the largest member, Amalthea, did not form on the present orbit, but that it was formed farther from the planet, or that it is a captured Solar System body. These moons, along with a number of as-yet-unseen inner moonlets, replenish and maintain Jupiter's faint ring system. Metis and Adrastea help to maintain Jupiter's main ring, while Amalthea and Thebe each maintain their own faint outer rings.

*Main group or Galilean moons — the four massive satellites: Ganymede, Callisto, Io, and Europa. With radii that are larger than any of the dwarf planets, they are some of the largest objects in the Solar System outside the Sun and the eight planets in terms of diameter. Respectively the first, third, fourth, and sixth largest natural satellites in the Solar System, they contain almost 99.999% of the total mass in orbit around Jupiter. The inner moons also participate in a 1:2:4 orbital resonance. Models suggest that they formed by slow accretion in the low-density Jovian subnebula—a disc of the gas and dust that existed around Jupiter after its formation—which lasted up to 10 million years in the case of Callisto.

Irregular satellites

The irregular satellites are substantially smaller objects with more distant and eccentric orbits. They form families with shared similarities in orbit (semi-major axis, inclination, eccentricity) and composition; it is believed that these are at least partially collisional families that were created when larger (but still small) parent bodies were shattered by impacts from asteroids captured by Jupiter's gravitational field. These families bear the names of their largest members. The identification of satellite families is tentative, but the following are typically listed:

Prograde satellites:

*Themisto is the innermost irregular moon and not part of a known family.

*The Himalia group is spread over barely 1.4 Gm in semi-major axis, 1.6° in inclination (27.5 ± 0.8°), and eccentricities between 0.11 and 0.25. It has been suggested that the group could be a remnant of the break-up of an asteroid from the main asteroid belt.

*Carpo is the outermost prograde moon and not part of a known family.

The irregular retrograde satellites are thought to have originally been asteroids that were captured by drag from the tenuous outer regions of Jupiter's accretion disk while the Solar system was still forming, and were later shattered by impacts. They are far enough from Jupiter that their orbits are significantly disturbed by the gravitational field of the Sun.

*S/2003 J 12 is the innermost of the retrograde moons, and is not part of a known family.

*The Carme group is spread over only 1.2 Gm in semi-major axis, 1.6° in inclination (165.7 ± 0.8°), and eccentricities between 0.23 and 0.27. It is very homogeneous in color (light red) and is believed to have originated from a D-type asteroid progenitor, possibly a Jupiter trojan.

*The Ananke group has a relatively wider spread than the previous groups, over 2.4 Gm in semi-major axis, 8.1° in inclination (between 145.7° and 154.8°), and eccentricities between 0.02 and 0.28. Most of the members appear gray, and are believed to have formed from the breakup of a captured asteroid.

*The Pasiphae group is quite dispersed, with a spread over 1.3 Gm, inclinations between 144.5° and 158.3°, and their eccentricities between 0.25 and 0.43. The colors also vary significantly, from red to grey, which might be the result of multiple collisions. Sinope, sometimes included into Pasiphae group, is red and given the difference in inclination, it could have been captured independently; Pasiphae and Sinope are also trapped in secular resonances with Jupiter.

*S/2003 J 2 is the outermost moon of Jupiter, and is not part of a known family.

Table

The moons of Jupiter are listed below by orbital period. Moons massive enough for their surfaces to have collapsed into a spheroid are highlighted in blue(^†); these are the four Galilean moons, which are comparable in size to Earth's Moon. The four inner moons have no background color. Irregular, captured moons are indicated by gray shading: light for prograde satellites, and dark gray for retrograde.

Order	Name	Pronunciation (IPA English pronunciation key)	Semi-major axis (km)	Orbital period (d)	Inclination (°)	Eccentricity	Discovery year	Discoverer	Group
1	Metis	ˈmiːtɨs				0.000 02	1979	Synnott (Voyager 1)	Inner
2	Adrastea	ˌædrəˈstiːə				0.0015	1979	Jewitt (Voyager 2)	Inner
3	Amalthea	ˌæməlˈθiːə				0.0032	1892	Barnard	Inner
4	Thebe	ˈθiːbi				0.0175	1979	Synnott (Voyager 1)	Inner
5	Io^†	ˈaɪ.oʊ				0.0041	1610	Galilei	Galilean
6	Europa^†	jʊˈroʊpə				0.0094	1610	Galilei	Galilean
7	Ganymede^†	ˈgænɨmiːd				0.0011	1610	Galilei	Galilean
8	Callisto^†	kəˈlɪstoʊ				0.0074	1610	Galilei	Galilean
9	Themisto	θɨˈmɪstoʊ		+129.87		0.2115	1975/2000	Kowal & Roemer/ Sheppard et al.	Themisto
10	Leda	ˈliːdə	11 187 781	+241.75		0.1673	1974	Kowal	Himalia
11	Himalia	haɪˈmeɪliə	11 451 971	+250.37		0.1513	1904	Perrine	Himalia
12	Lysithea	laɪˈsɪθiə	11 740 560	+259.89		0.1322	1938	Nicholson	Himalia
13	Elara	ˈɛlərə	11 778 034	+261.14		0.1948	1905	Perrine	Himalia
14	S/2000 J 11		12 570 424	+287.93		0.2058	2001	Sheppard et al.	Himalia
15	Carpo	ˈkɑrpoʊ	17 144 873	+458.62		0.2735	2003	Sheppard et al.	Carpo
16	S/2003 J 12		17 739 539	−482.69	142.680°	0.4449	2003	Sheppard et al.	?
17	Euporie	juːˈpɔərɨ.i	19 088 434	−538.78	144.694°	0.0960	2002	Sheppard et al.	Ananke
18	S/2003 J 3		19 621 780	−561.52	146.363°	0.2507	2003	Sheppard et al.	Ananke
19	S/2003 J 18		19 812 577	−569.73	147.401°	0.1569	2003	Gladman et al.	Ananke
20	Thelxinoe	θɛlkˈsɪnoʊ.i	20 453 753	−597.61	151.292°	0.2684	2003	Sheppard et al.	Ananke
21	Euanthe	juːˈænθi	20 464 854	−598.09	143.409°	0.2000	2002	Sheppard et al.	Ananke
22	Helike	ˈhɛlɨki	20 540 266	−601.40	154.586°	0.1374	2003	Sheppard et al.	Ananke
23	Orthosie	ɔrˈθɒsɨ.i	20 567 971	−602.62	142.366°	0.2433	2002	Sheppard et al.	Ananke
24	Iocaste	ˌaɪ.əˈkæsti	20 722 566	−609.43	147.248°	0.2874	2001	Sheppard et al.	Ananke
25	S/2003 J 16		20 743 779	−610.36	150.769°	0.3184	2003	Gladman et al.	Ananke
26	Praxidike	prækˈsɪdɨki	20 823 948	−613.90	144.205°	0.1840	2001	Sheppard et al.	Ananke
27	Harpalyke	hɑrˈpælɨki	21 063 814	−624.54	147.223°	0.2440	2001	Sheppard et al.	Ananke
28	Mneme	ˈniːmi	21 129 786	−627.48	149.732°	0.3169	2003	Gladman et al.	Ananke
29	Hermippe	hɚˈmɪpi	21 182 086	−629.81	151.242°	0.2290	2002	Sheppard et al.	Ananke?
30	Thyone	θaɪˈoʊni	21 405 570	−639.80	147.276°	0.2525	2002	Sheppard et al.	Ananke
31	Ananke	əˈnæŋki	21 454 952	−642.02	151.564°	0.3445	1951	Nicholson	Ananke
32	S/2003 J 17		22 134 306	−672.75	162.490°	0.2379	2003	Gladman et al.	Carme
33	Aitne	ˈaɪtni	22 285 161	−679.64	165.562°	0.3927	2002	Sheppard et al.	Carme
34	Kale	ˈkeɪli	22 409 207	−685.32	165.378°	0.2011	2002	Sheppard et al.	Carme
35	Taygete	teiˈɪdʒɨti	22 438 648	−686.67	164.890°	0.3678	2001	Sheppard et al.	Carme
36	S/2003 J 19		22 709 061	−699.12	164.727°	0.1961	2003	Gladman et al.	Carme
37	Chaldene	kælˈdiːni	22 713 444	−699.33	167.070°	0.2916	2001	Sheppard et al.	Carme
38	S/2003 J 15		22 720 999	−699.68	141.812°	0.0932	2003	Sheppard et al.	Ananke?
39	S/2003 J 10		22 730 813	−700.13	163.813°	0.3438	2003	Sheppard et al.	Carme?
40	S/2003 J 23		22 739 654	−700.54	148.849°	0.3930	2004	Sheppard et al.	Pasiphaë
41	Erinome	ɨˈrɪnəmi	22 986 266	−711.96	163.737°	0.2552	2001	Sheppard et al.	Carme
42	Aoede	eɪˈiːdi	23 044 175	−714.66	160.482°	0.6011	2003	Sheppard et al.	Pasiphaë
43	Kallichore	kəˈlɪkəri	23 111 823	−717.81	164.605°	0.2041	2003	Sheppard et al.	Carme?
44	Kalyke	ˈkælɨki	23 180 773	−721.02	165.505°	0.2139	2001	Sheppard et al.	Carme
45	Carme	ˈkɑrmi	23 197 992	−721.82	165.047°	0.2342	1938	Nicholson	Carme
46	Callirrhoe	kəˈlɪroʊ.i	23 214 986	−722.62	139.849°	0.2582	2000	Gladman et al.	Pasiphaë
47	Eurydome	jʊˈrɪdəmi	23 230 858	−723.36	149.324°	0.3769	2002	Sheppard et al.	Pasiphaë?
48	Pasithee	pəˈsɪθɨ.i	23 307 318	−726.93	165.759°	0.3288	2002	Sheppard et al.	Carme
49	Cyllene	sɨˈliːni	23 396 269	−731.10	140.148°	0.4115	2003	Sheppard et al.	Pasiphaë
50	Eukelade	juːˈkɛlədi	23 483 694	−735.20	163.996°	0.2828	2003	Sheppard et al.	Carme
51	S/2003 J 4		23 570 790	−739.29	147.175°	0.3003	2003	Sheppard et al.	Pasiphaë
52	Pasiphaë	pəˈsɪfeɪ.i	23 609 042	−741.09	141.803°	0.3743	1908	Gladman et al.	Pasiphaë
53	Hegemone	hɨˈdʒɛməni	23 702 511	−745.50	152.506°	0.4077	2003	Sheppard et al.	Pasiphaë
54	Arche	ˈɑrki	23 717 051	−746.19	164.587°	0.1492	2002	Sheppard et al.	Carme
55	Isonoe	aɪˈsɒnoʊ.i	23 800 647	−750.13	165.127°	0.1775	2001	Sheppard et al.	Carme
56	S/2003 J 9		23 857 808	−752.84	164.980°	0.2761	2003	Sheppard et al.	Carme
57	S/2003 J 5		23 973 926	−758.34	165.549°	0.3070	2003	Sheppard et al.	Carme
58	Sinope	sɨˈnoʊpi	24 057 865	−762.33	153.778°	0.2750	1914	Nicholson	Pasiphaë
59	Sponde	ˈspɒndi	24 252 627	−771.60	154.372°	0.4431	2002	Sheppard et al.	Pasiphaë
60	Autonoe	ɔːˈtɒnoʊ.i	24 264 445	−772.17	151.058°	0.3690	2002	Sheppard et al.	Pasiphaë
61	Kore	ˈkɔəri	23 345 093	−776.02	137.371°	0.1951	2003	Sheppard et al.	Pasiphaë
62	Megaclite	ˌmɛgəˈklaɪti	24 687 239	−792.44	150.398°	0.3077	2001	Sheppard et al.	Pasiphaë
63	S/2003 J 2		30 290 846		153.521°	0.1882	2003	Sheppard et al.	?