Moons of Jupiter

thumb|upright=1.5|A montage of Jupiter and its four largest moons (distance and sizes not to scale)

There are 115 known moons of the planet Jupiter . the largest Galilean, Ganymede, is the ninth largest object in the Solar System, after the Sun and seven of the planets, Ganymede being larger than Mercury. All other Jovian moons are less than in diameter, with most barely exceeding . Their orbital shapes range from nearly perfectly circular to highly eccentric and inclined, and many revolve in the direction opposite to Jupiter's rotation (retrograde motion).

Origin and evolution

thumb|upright=1.3|The relative masses of the Jovian moons. Those smaller than Europa are not visible at this scale, and combined would only be visible at 100× magnification.

Jupiter's regular satellites are believed to have formed from a circumplanetary disk, a ring of gravitated gas and solid debris analogous to a protoplanetary disk. They may be the remnants of a score of Galilean-mass satellites that formed early in Jupiter's history. The current Galilean moons were still affected, falling into and being partially protected by an orbital resonance with each other, which still exists for Io, Europa, and Ganymede: they are in a 1:2:4 resonance. Ganymede's larger mass means that it would have migrated inward at a faster rate than Europa or Io.

The outer, irregular moons are thought to have originated from captured asteroids, whereas the proto-lunar disk was still massive enough to absorb much of their momentum and thus capture them into orbit. Many are believed to have been broken up by mechanical stresses during capture, or afterward by collisions with other small bodies, producing the moons we see today. However, the first certain observations of Jupiter's satellites were those of Galileo Galilei in 1609. By January 1610, he had sighted the four massive Galilean moons with his 20× magnification telescope, and he published his results in March 1610.

Simon Marius had independently discovered the moons one day after Galileo, although he did not publish his book on the subject until 1614. Even so, the names Marius assigned are used today: Ganymede, Callisto, Io, and Europa. However, these names fell out of favor until the 20th century. The astronomical literature instead simply referred to "Jupiter I", "Jupiter II", etc., or "the first satellite of Jupiter", "Jupiter's second satellite", and so on. whereas the rest of the moons remained unnamed and were usually numbered in Roman numerals V (5) to XII (12). Jupiter V was discovered in 1892 and given the name Amalthea by a popular though unofficial convention, a name first used by French astronomer Camille Flammarion.

The other moons were simply labeled by their Roman numeral (e.g. Jupiter IX) in the majority of astronomical literature until the 1970s. Several different suggestions were made for names of Jupiter's outer satellites, but none were universally accepted until 1975 when 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 still to be discovered. All of Jupiter's satellites from XXXIV (Euporie) onward are named after descendants of Jupiter or Zeus, Some of the most recently confirmed moons have not received names. These moons, along with a number of seen and as-yet-unseen inner moonlets (see Amalthea moonlets), replenish and maintain Jupiter's faint ring system. Metis and Adrastea help to maintain Jupiter's main ring, whereas Amalthea and Thebe each maintain their own faint outer rings.

Main group or Galilean moons: Io, Europa, Ganymede and Callisto. They are some of the largest objects in the Solar System outside the Sun and the eight planets in terms of mass, larger than any known dwarf planet. Ganymede exceeds (and Callisto nearly equals) even the planet Mercury in diameter, though they are less massive. They are respectively the fourth-, sixth-, first-, and third-largest natural satellites in the Solar System, containing approximately 99.997% of the total mass in orbit around Jupiter, while Jupiter is almost 5,000 times more massive than the Galilean moons. The inner moons are 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. Europa, Ganymede, and Callisto are suspected of having subsurface water oceans, and Io may have a subsurface magma ocean.

Irregular satellites

thumb|300px|Orbits and positions of Jupiter's irregular satellites as of 1 January 2021. Prograde orbits are colored blue while retrograde orbits are colored red.

thumb|upright=1.5|107 irregular moons of Jupiter plotted by semi-major axis and inclination .

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 is not part of a known family.

! Name

! class="unsortable" |

! class="unsortable" |Image

! data-sort-type="number" |Abs.mag.(km)

! data-sort-type="number" style="max-width:6em" |Mass( kg)

! data-sort-type="number" style="max-width:6em" |Semi-major axis(d)

! data-sort-type="number" style="max-width:6em" |Inclination|

|- id="Metis" style="background:#fff;"

||XVI

|Metis

|style="background:black;"|50px

|10.5

|43.4 (60 × 40 × 34)

||123.9

||+0.2959 (+7h 06m 04s)

|0.060

|0.0002

|1979

|1980

|Synnott (Voyager 1)

|Inner

|- id="Adrastea" style="background:#fff;"

||XV

|Adrastea

|style="background:black;"|50px

|12.0

||16.5 (20 × 16 × 14)

||2.0

||+0.2994 (+7h 11m 4s)

|0.030

|0.0015

|1979

|Jewitt (Voyager 2)

|Inner

|- id="Amalthea" style="background:#fff;"

||V

|Amalthea

|style="background:black;"|50px

|7.1

|style="max-width:5em" |167.2 (250 × 146 × 128)

||2096.4

||+0.4990 (+11h 58m 37s)

|0.374

|0.0032

|1892

|Barnard

|Inner

|- id="Thebe" style="background:#fff;"

||XIV

|Thebe

|style="background:black;"|50px

|9.0

||98.5 (116 × 98 × 84)

||700.0

||+0.6753 (+16h 12m 27s)

|1.076

|0.0175

|1979

|1980

|Synnott (Voyager 1)

|Inner

|- id="Io" style="background:#ccf;"

||I

| Io♠

|style="background:black;"|alt=|center|50px

| -1.7

|style="max-width:5em"|

||89284845.2

||+1.7693 (+1d 18h 27m 46s)

|0.050

|0.0040

|1610

|Galileo

|Galilean

|- id="Europa" style="background:#ccf;"

||II

| Europa♠

|style="background:black;"|50px

| -1.4

||47987653.0

||+3.5504 (+3d 13h 12m 38s)

|0.470

| Europa || 540 The Voyager 1 and Voyager 2 probes visited Jupiter in 1979, discovering the volcanic activity on Io and the presence of water ice on the surface of Europa.

The Galileo spacecraft was the first to enter orbit around Jupiter, arriving in 1995 and studying it until 2003. During this period, Galileo gathered a large amount of information about the Jovian system, making close approaches to all of the Galilean moons and finding evidence for thin atmospheres on three of them, as well as the possibility of liquid water beneath the surfaces of Europa, Ganymede, and Callisto. It also discovered a magnetic field around Ganymede.

Then the Cassini probe to Saturn flew by Jupiter in 2000 and collected data on interactions of the Galilean moons with Jupiter's extended atmosphere. The New Horizons spacecraft flew by Jupiter in 2007 and made improved measurements of its satellites' orbital parameters.

In 2016, the Juno spacecraft imaged the Galilean moons from above their orbital plane as it approached Jupiter orbit insertion, creating a time-lapse movie of their motion. With a mission extension, Juno has since begun close flybys of the Galileans, flying by Ganymede in 2021 followed by Europa and Io in 2022. It flew by Io again in late 2023 and once more in early 2024.

Notes

</references>

External links

Scott S. Sheppard: Moons of Jupiter
Scott S. Sheppard: The Jupiter Satellite and Moon Page
Jupiter Moons by NASA's Solar System Exploration
Archive of Jupiter System Articles in Planetary Science Research Discoveries
Tilmann Denk: Outer Moons of Jupiter

Origin and evolution

Irregular satellites

See also

Notes

External links