Moons of Jupiter

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In astronomy, the moons of Jupiter are Jupiter's natural satellites. Sixty-three moons orbiting Jupiter have been discovered.

[edit] Discovery

Although claims are made for the observation of one of Jupiter's moons by Chinese astronomer Gan De in 364 BC, the first certain observations of Jupiter's satellites are those of Galileo Galilei in 1610, who sighted the four large Galilean moons with his 33x telescope.

No additional satellites were discovered until E.E. Barnard observed Amalthea in 1892. Further discoveries, aided by telescopic photography, followed quickly over the course of the twentieth century, and by 1975, before the Voyagers reached Jupiter, the planet was known to have at least thirteen satellites.

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.

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

[edit] Table of Jupiter's moons

The moons of Jupiter are listed below by orbital period, from shortest to longest. 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. Irregular, captured moons are indicated by grey shading: light grey for prograde satellites, dark grey for retrograde.

• ⁽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⁾ Periods with negative values are retrograde.
• ⁽⁵⁾ Computed from IAG Travaux 2001 for Metis through Callisto, showing inclination to Jupiter's equator; taken from IAU-MPC Satellites Ephemeris Service orbital elements for the others, using inclination to the local Laplace plane.

[edit] Grouping the moons

As for all four giant planets, the Jupiter's satellites are categorised into two main categories:

• Regular satellites consisting of the Amalthea group of inner moons and the four Galilean moons, formed in situ
• Irregular satellites, far-reaching, highly eccentrical, substantially smaller objects generally picked up on Jupiter's space journey

The first diagram illustrates the orbits of the irregular satellites of Jupiter discovered so far. The eccentricity of the orbits is represented by the segments (extending from the pericentre to the apocentre) with the inclination represented on Y axis. The satellites above the axis are prograde, the satellites beneath are retrograde. The X axis is labelled in Gm (million km) and the fraction of the Hill sphere's (gravitational influence) radius (~53 Gm for Jupiter). The following diagram shows separately the distribution of inclination versus eccentricity for the retrograde satellites, facilitating the identification of the groupings.

[edit] Prograde irregular moons

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.

Themisto and Carpo are isolated in space.

[edit] Retrograde irregular moons

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.

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.

S/2003 J 12, and S/2003 J 2, the most exterior moon, are again isolated.

[edit] Naming

Main article: Naming of natural satellites

The seven satellites discovered between 1904 and 1951—Himalia, Elara, Pasiphaë, Sinope, Lysithea, Carme and Ananke—were not officially named until 1975, 24–71 years after being discovered. They were for the most part simply known by their Roman numeral designations, Jupiter VI through Jupiter XII, although various names were proposed in 1955, 1962, and 1973.

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
• Callisto and asteroid 204 Kallisto

See also: Name conflicts of solar system objects

[edit] See also

• Galilean moons
• Jupiter's moons in fiction
• Natural satellites of Earth · Mars · Saturn · Uranus · Neptune

[edit] Notes

[edit] References

• Scott S. Sheppard, David C. Jewitt An abundant population of small irregular satellites around Jupiter, Nature, 423 (May 2003), pp.261-263 Full text(pdf).
• Scott S. Sheppard, David C. Jewitt, Carolyn Porco Jupiter's outer satellites and Trojans, In: Jupiter. The planet, satellites and magnetosphere Edited by Fran Bagenal, Timothy E. Dowling, William B. McKinnon. Cambridge planetary science, Vol. 1, Cambridge, UK: Cambridge University Press, ISBN 0-521-81808-7, 2004, p. 263 - 280. Full text(pdf).

[edit] External links

• Jupiter's Moons by NASA's Solar System Exploration
• Jupiter satellite data
• 43 more moons orbiting Jupiter

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