Jupiter's natural satellites

Jupiter has 63 known natural satellites.

Discovery of the moons

The first moons of Jupiter to be discovered were the large Galilean moons, discovered by Galileo in 1610. An earlier discovery by ancient Chinese astronomer Gan De may have occurred in 364 BC. Over the next four centuries after Galileo, nine smaller moons were discovered by ground-based astronomers.

The Voyager 1 mission discovered three inner moons in 1979, bringing the total then known to 16 (17 if one counted Themisto, which had been found but then lost in 1975). The total rested there until 1999. Since then, researchers using sensitive ground-based detectors have recovered Themisto and found a further 46 tiny moons in long, eccentric, generally retrograde orbits. They average 3 kilometres in diameter, and the largest is barely 9 km 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. The total number of known moons of Jupiter now stands at 63, currently the most of any planet in the solar system. Many additional tiny moons may exist that have not yet been discovered.

The most recent discoveries

On October 6 1999, the Spacewatch project discovered an asteroid, 1999 UX₁₈. But it was soon realised that this was in fact a previously undiscovered moon of Jupiter, now called Callirrhoe. One year later, between November 23 and December 5, 2000, the team led by Scott S. Sheppard and David C. Jewitt of the University of Hawaii began a systematic search for small irregular moons of Jupiter. The other members of the team included, at various times, Yanga R. Fernández, Eugene A. Magnier, Scott Dahm, Aaron Evans, Henry H. Hsieh, Karen J. Meech, John L. Tonry, David J. Tholen (all from the University of Hawaii), Jan Kleyna (Cambridge University), Brett J. Gladman (University of Toronto), John J. Kavelaars (Hertzberg Institute of Astrophysics), Jean-Marc Petit (Observatoire de Besançon) and Rhiannon Lynne Allen (University of Michigan / University of British Columbia).

The team used the world's two largest CCD cameras, mounted on two of the thirteen telescopes atop Mauna Kea in Hawaii: the Subaru (8.3 m diameter) and the Canada-France-Hawaii (3.6 m). The 2000 observations revealed ten new moons, putting the count at 28 (Themisto had been rediscovered at the beginning of 2000).

The following year, on December 9-11, 2001, eleven other moons were discovered, bringing the total to 39. The year 2002 bore less fruit, netting only one moon, Arche. However, four months later, between February 5 and 9, 2003, 23 more moons were found, making for a complete sum of 63 moons.

References:

Table of known moons

The Jovian moons are listed here by orbital period, from shortest to longest. Moons massive enough for their surfaces to have collapsed into a spheroid are highlighted in purple; these are the "Galilean Moons", which are comparable in size to Earth's moon. Irregular (captured) moons are indicated by light grey.

(Pronunciation respelling key)

Name		Diameter (km)	Mass (kg)	Orbital radius (km)⁽³⁾	Orbital period (d)⁽³⁾	Inclination (°)⁽⁴⁾ (to Jupiter's equator)	Eccentricity	Group
Metis	mee'-təs	43	1.2E+17	127 690⁽¹⁾	0.294780⁽²⁾	0.000°	0.0012	Amalthea
Adrastea	ad'-rə-stee'-ə	26×20×16	7.5E+15	128 690⁽¹⁾	0.29826⁽²⁾	0.000°	0.0018
Amalthea	am'-əl-thee'-ə	262×146×134	2.1E+18	181 170⁽¹⁾	0.49817905⁽²⁾	0.360°	0.0031
Thebe	thee'-bee	110×90	1.5E+18	221 700⁽¹⁾	0.6745⁽²⁾	0.901°	0.0177
Io	eye'-oe	3660.0×3637.4×3630.6	8.9E+22	421 700⁽¹⁾	1.769137786⁽²⁾	0.050°	0.0041	Galileans
Europa	ew-roe'-pə	3121.6	4.8E+22	671 034⁽¹⁾	3.551181041⁽²⁾	0.471°	0.0094
Ganymede	gan'-ə-meed	5262.4	1.5E+23	1 070 412⁽¹⁾	7.15455296⁽²⁾	0.204°	0.0011
Callisto	kə-lis'-toe	4820.6	1.1E+23	1 882 709⁽¹⁾	16.6890184⁽²⁾	0.205°	0.0074
Themisto	thə-mis'-toe	8	6.9E+14	7 391 645	129.827611	15.346°	0.2006	Themisto
Leda	lee'-də	20	1.1E+16	11 097 245	238.824159	27.210°	0.1854	Himalia
Himalia	hye-mal'-ee-ə	170	6.7E+18	11 432 435	249.726305	29.590°	0.1443
Lysithea	lye-sith'-ee-ə	36	6.3E+16	11 653 225	256.995413	25.771°	0.1132
Elara	ee'-lər-ə	86	8.7E+17	11 683 115	257.984888	30.663°	0.1723
S/2000 J 11		4	9.0E+13	12 570 575	287.931046	26.169°	0.2058
Carpo	kar'-poe	3	4.5E+13	17 144 875	458.624818	55.098°	0.2736	Carpo
S/2003 J 12		1	1.5E+12	17 739 540	482.691255	134.861°	0.4449	?
Euporie	ew-por'-ee-ə	2	1.5E+13	19 088 435	538.779839	131.854°	0.0960	Ananke?
S/2003 J 3		2	1.5E+13	19 621 780	561.517739	111.592°	0.2507
S/2003 J 18		2	1.5E+13	19 812 575	569.728015	98.461°	0.1570
Thelxinoe	thel-zin'-oe-ee	2	1.5E+13	20 453 755	597.606695	102.844°	0.2685	Ananke?
Euanthe	ew-an'-thee	3	4.5E+13	20 464 855	598.093368	123.649°	0.2000	Ananke
Helike	hel'-ə-kee	4	9.0E+13	20 540 265	601.401918	120.908°	0.1375	Ananke?
Orthosie	or-thoe'-see-ə	2	1.5E+13	20 567 970	602.619143	101.861°	0.2433	Ananke?
Iocaste	eye'-oe-kas'-tee	5	1.9E+14	20 722 565	609.426611	127.043°	0.2874	Ananke
S/2003 J 16		2	1.5E+13	20 743 780	610.362159	149.279°	0.3185
Ananke	ə-nang'-kee	28	3.0E+16	20 815 225	613.518491	149.526°	0.3963
Praxidike	prak-sid'-ə-kee	7	4.3E+14	20 823 950	613.904099	132.099°	0.1840
Harpalyke	har-pal'-ə-kee	4	1.2E+14	21 063 815	624.541797	143.944°	0.2441
Hermippe	hər-mip'-ee	4	9.0E+13	21 182 085	629.809040	149.058°	0.2290	Ananke?
Thyone	thye-oe'-nee	4	9.0E+13	21 405 570	639.802554	116.088°	0.2526	Ananke
Mneme	nee'-mee	2	1.5E+13	21 427 110	640.768660	147.647°	0.2214	Ananke
S/2003 J 17		2	1.5E+13	22 134 305	672.751882	139.842°	0.2379	Carme
Aitne	et'-nee	3	4.5E+13	22 285 160	679.641347	143.251°	0.3927
Kale	kay'-lee	2	1.5E+13	22 409 210	685.323873	133.342°	0.2011
Taygete	tay-ij'-ə-tee	5	1.6E+14	22 438 650	686.674715	140.521°	0.3678
S/2003 J 19		2	1.5E+13	22 709 060	699.124764	140.956°	0.1961
Chaldene	kal-dee'-nee	4	7.5E+13	22 713 445	699.326904	119.572°	0.2916
S/2003 J 15		2	1.5E+13	22 721 000	699.676116	109.168°	0.0932	Ananke?
S/2003 J 10		2	1.5E+13	22 730 815	700.129403	115.021°	0.3438	Carme?
S/2003 J 23		2	1.5E+13	22 739 655	700.537990	137.576°	0.3931	Pasiphaë
Erinome	err-rin'-ə-mee	3	4.5E+13	22 986 265	711.964625	143.354°	0.2552	Carme
Aoede	ay-ee'-dee	4	9.0E+13	23 044 175	714.656754	112.763°	0.6012	Pasiphaë
Kallichore	kə-lik'-ə-ree	2	1.5E+13	23 111 825	717.806112	141.240°	0.2042	Carme?
Kalyke	kal'-ə-kee	5	1.9E+14	23 180 775	721.020662	137.125°	0.2140	Carme
Eurydome	ew-rid'-ə-mee	3	4.5E+13	23 230 860	723.358859	143.033°	0.3770	Pasiphaë?
S/2003 J 14		2	1.5E+13	23 238 595	723.720459	138.885°	0.2462	Pasiphaë
Pasithee	pə-sith'-ee-ə	2	1.5E+13	23 307 320	726.932963	144.112°	0.3289	Carme
Cyllene	sə-lee'-nee	2	1.5E+13	23 396 270	731.098603	115.507°	0.4116	Pasiphaë
Eukelade	ew-kel'-ə-dee	4	9.0E+13	23 483 695	735.199980	118.384°	0.2829	Carme
S/2003 J 4		2	1.5E+13	23 570 790	739.293961	98.660°	0.3003	Pasiphaë
Hegemone	hə-jem'-ə-nee	3	4.5E+13	23 702 510	745.500007	150.314°	0.4077	Pasiphaë
Arche	ar'-kee	3	4.5E+13	23 717 050	746.185469	146.289°	0.1492	Carme
Carme	kar'-mee	46	1.3E+17	23 734 465	747.008062	120.659°	0.3122
Isonoe	eye-son'-oe-ee	4	7.5E+13	23 832 630	751.646937	118.554°	0.1665
S/2003 J 9		1	1.5E+12	23 857 810	752.838751	135.452°	0.2762
S/2003 J 5		4	9.0E+13	23 973 925	758.341296	117.922°	0.3071
Pasiphaë	pə-sif'-ə-ee	60	3.0E+17	24 094 770	764.082032	143.037°	0.2953	Pasiphaë
Sinope	sə-noe'-pee	38	7.5E+16	24 214 390	769.779665	146.657°	0.2468
Sponde	spon'-dee	2	1.5E+13	24 252 625	771.603566	112.409°	0.4432
Autonoe	aw-ton'-oe-ee	4	9.0E+13	24 264 445	772.167762	129.073°	0.3690
Callirrhoe	kə-lirr'-oe-ee	9	8.7E+14	24 356 030	776.543335	131.895°	0.2644
Megaclite	meg'-ə-klye'-tee	5	2.1E+14	24 687 240	792.436947	143.760°	0.3078
S/2003 J 2		2	1.5E+13	30 290 845	1077.018006	151.523°	0.1882	?

⁽¹⁾ Computed using the IAU-MPC Satellites Ephemeris Service µ value
⁽²⁾ Source: JPL/NASA
⁽³⁾ Source (for Themisto outward): IAU-MPC Satellites Ephemeris Service
⁽⁴⁾ Computed from IAG Travaux 2001 for Metis through Callisto, IAU-MPC Satellites Ephemeris Service orbital elements for the others

Grouping the moons

The interior groups - the four inner moons and the Galileans - seem natural. Themisto is isolated in space. The Himalia group is "tight", spread over barely 1.4 Gm in semi-major axis and 1.6° in inclination (27.5 ± 0.8°). The eccentricities vary between 0.11 and 0.25. Carpo and S/2003 J 12 are two other isolated cases, and so is S/2003 J 2, the most exterior moon.

What is left of the outer retrograde irregular satellites of Jupiter can be grouped into three families, based on shared orbital characteristics and bearing the name of the largest member in each case. These families are clumps in semi-major axis, but also in inclination and in eccentricity. In the two plots below, Carme's group is in orange and Ananke's in yellow.

Carme's group is obvious, centered on a = 23 404 Mm; i = 165.2±0.3° and e = 0.238–0.272. Only S/2003 J 10 seems somewhat apart, because of its great eccentricity.

Ananke's group is centered on a = 21 276 Mm; i = 149.0±0.5° and e = 0.216–0.244; but its borders are less definite. The eight core members (S/2003 J 16, Mneme, Euanthe, Orthosie, Harpalyke, Praxidike, Thyone, Thelxinoe, Ananke, Iocaste) are well-clumped, but the attribution of the remaining eight members to the group is debatable to varying degrees.

Pasiphaë's group, finally, picks up the remainder, with the exception of the moons at the inner and outer limits of the groups (S/2003 J 12 and S/2003 J 2); it is centered on a = 23 624 Mm; i = 151.4±6.9° and e = 0.156–0.432 (note the much larger spreads). If it is real, it must be ancient to explain the dispersion of its membership.

Naming notes

Some asteroids share the same names as moons of Jupiter: 9 Metis, 38 Leda, 52 Europa, 85 Io, 113 Amalthea, 239 Adrastea.

A couple of asteroids shared the names of Jovian moons until spelling differences were made permanent by the IAU. Those contrasting pairs are the moon Ganymede and the asteroid 1036 Ganymed; and the moon Callisto and the asteroid 204 Kallisto. The moon Themisto purposely uses a name derived from the longer gentive form of the source of the name for asteroid 24 Themis.

Note that the satellites discovered between 1904 and 1951 (Himalia, Elara, Pasiphaë, Sinope, Lysithea, Carme and Ananke) were not officially named until 1975, 24 years after the last satellite was discovered. They were simply known by their Roman numeral designations (Jupiter VI through Jupiter XII). See Naming of natural satellites.

External links

Jupiter's moons

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