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| The Solar System - The Outer Solar System |
Jupiter is a giant planet with a mass one-thousandth of that of the Sun, but is two and a half times that of all the other planets in the Solar System combined. Jupiter is a gas giant, along with Saturn. Jupiter is primarily composed of hydrogen with a quarter of its mass being helium, although helium only comprises about a tenth of the number of molecules. It may also have a rocky core of heavier elements, but like the other giant planets, Jupiter lacks a well-defined solid surface. Because of its rapid rotation, the planet's shape is that of an oblate spheroid. The outer atmosphere is visibly segregated into several bands at different latitudes, resulting in turbulence and storms along their interacting boundaries. A prominent result is the Great Red Spot, a giant storm that is known to have existed since at least the 17th century when it was first seen by telescope. Surrounding Jupiter is a faint planetary ring system and a powerful magnetosphere.
- Size: 139,822+/-12 km
- Orbital period of 11.86 years at a distance of 5.20 (4.95 AU to 5.46).
- Type: planet
- Orbit:
- Brangogne Satellite City
- Miranda Satellite City; 14th and 15th districts
- White Flora Satellite City
Halo Ring
The outer edge of the Halo Ring coincides with the inner boundary of the main ring. From this radius the ring becomes rapidly thicker towards Jupiter. The inner boundary of the halo is relatively sharp. Its shape resembles a thick torus without clear internal structure. The large thickness of the halo can be attributed to the excitation of orbital inclinations and eccentricities of dust particles by the electromagnetic forces in the Jovian magnetosphere.
- 92,000-122,500 km from Jupiter
- Width: 30,500 km
- Depth: 12,500 km
Main Ring
The narrow and relatively thin main ring is the brightest part of Jupiter's ring system. Its outer edge coincides with the orbit Adrastea. Its inner edge is not marked by any satellite. The outer boundary of the main ring, slightly beyond the orbit of Adrastea, is very steep. The orbit of the moon is marked by a gap in the ring, so there is a thin ringlet just outside its orbit. There is another ringlet just inside Adrastean orbit, followed by a gap of unknown origin located at about 128,500 km. The third ringlet is found inward of the central gap, outside the orbit of Metis. The ring's brightness drops sharply just outward of the Metidian orbit, forming the Metis notch.
- 122,500-129,000 km from Jupiter
- Width: 6,500 km
- Depth: 30-300 km
Metis
Metis is tidally locked to Jupiter, and its shape is strongly asymmetrical, with one of the diameters being almost twice as large as the smallest one. It orbits within the main ring of Jupiter, and is thought to be a major contributor of material to the rings.
- Size: 43.0+/-4.0 km
- Orbital period of 0.294 days at a distance of 128,000 (127,974 to 128,026) km.
- Type: satellite
Adrastea
Adrastea orbits at the edge of Jupiter's Main Ring, and is thought to be the main contributor of material to the Rings of Jupiter. Very little is known about the moon's physical characteristics, other than its size and the fact that it is tidally locked to Jupiter.
- Size: 16.4+/-4.0 km
- Orbital period of 0.298 days at a distance of 129,000 km.
- Type: satellite
Amalthea Gossamer Ring
A very faint structure with a rectangular cross section. Its inner boundary is not clearly defined because of the presence of the much brighter main ring and halo. The Amalthea gossamer ring is actually the brightest near its top and bottom edges and becomes gradually brighter towards Jupiter; one of the edges is often brighter than another. The outer boundary of the ring is relatively steep; the ring's brightness drops abruptly just inward of the orbit of Amalthea, although it may have a small extension beyond the orbit of the satellite ending near a 4:3 resonance with Thebe.
- 129,000-182,000 km from Jupiter
- Width: 53,000 km
- Depth: 2,300 km
Amalthea
Amalthea is within the outer edge of the Amalthea Gossamer Ring, which is formed from dust ejected from its surface. Amalthea is irregularly shaped and reddish in color, it is thought to consist of porous water ice with unknown amounts of other materials. Its surface features include large craters and ridges.
- Size: 167+/-4.0 km
- Orbital period of 0.498 days at a distance of 181,366 (181,150 to 182,840) km.
- Type: satellite
Thebe Gossamer Ring
The faintest Jovian ring. It appears as a very faint structure with a rectangular cross section. Its inner boundary is not clearly defined because of the presence of the much brighter main ring and halo. The Thebe gossamer ring is brightest near its top and bottom edges and gradually becomes brighter towards Jupiter. There is a barely visible continuation of the ring beyond the orbit of Thebe, extending up to 280,000 km and called the Thebe Extension.
- 129,000-226,000 km from Jupiter
- Width: 97,000 km
- Depth: 8,400 km
Thebe
Thebe orbits within the outer edge of the Thebe gossamer ring that is formed from dust ejected from its surface. It is irregularly shaped and reddish in colour, and is thought to consist of porous water ice with unknown amounts of other materials. Its surface features include large craters and high mountains - some of them are comparable to the size of the moon itself.2]
- Size: 98.6+/-4.0 km
- Orbital period of 0.67 days at a distance of 221,889 (218,000 to 226,400) km.
- Type: satellite
Io has the highest density of all the moons, and is the driest known object in the Solar System. With over 400 active volcanoes, Io is the most geologically active object in the Solar System. This extreme geologic activity is the result of tidal heating from friction generated within Io's interior as it is pulled between Jupiter and the other Galilean satellites - Europa, Ganymede and Callisto. Several volcanoes produce plumes of sulfur and sulfur dioxide that climb as high as 500 km above the surface. Io's surface is also dotted with more than 100 mountains that have been uplifted by extensive compression at the base of Io's silicate crust. Unlike most satellites in the outer Solar System, which are mostly composed of water ice, Io is primarily composed of silicate rock surrounding a molten iron or iron sulfide core. Most of Io's surface is composed of extensive plains coated with sulfur and sulfur dioxide frost.
Volcanic plumes and lava flows produce large surface changes and paint the surface in various subtle shades of yellow, red, white, black, and green, largely due to allotropes and compounds of sulfur. Numerous extensive lava flows, several more than 500 km in length, also mark the surface. The materials produced by this volcanism make up Io's thin, patchy atmosphere and Jupiter's extensive magnetosphere. Io's volcanic ejecta also produce a large plasma torus around Jupiter.
- Size: 3643.2+/-1.0 km
- Orbital period of 1.77 days at a distance of 421,700 (420,000 to 423,400) km.
- Type: satellite
Europa is primarily made of silicate rock and has a water-ice crust and probably an iron-nickel core. It has a tenuous atmosphere composed primarily of oxygen. Its surface is striated by cracks and streaks, whereas craters are relatively rare. It has the smoothest surface of any known solid object in the Solar System. The apparent youth and smoothness of the surface have led to the hypothesis that a water ocean exists beneath it, which could conceivably serve as an abode for extraterrestrial life. This hypothesis proposes that heat from tidal flexing causes the ocean to remain liquid and drives geological activity similar to plate tectonics.
"Clay-like minerals", often associated with "organic material", have been detected on the icy crust of Europa. Europa may have periodically occurring plumes of water 200 km high. These plumes appear when Europa is at its farthest point from Jupiter, and are not seen when Europa is at its closest point to Jupiter, in agreement with tidal force modeling predictions.
Europa has emerged as one of the top locations in the Solar System in terms of potential habitability and the possibility of hosting life. Life could exist in its under-ice ocean, perhaps subsisting in an environment similar to Earth's deep-ocean hydrothermal vents. Sea salt from a subsurface ocean may likely be coating some geological features on Europa, suggesting that the ocean is interacting with the seafloor.
- Size: 3,121.6+/-1.0 km
- Orbital period of 3.55 days at a distance of 670,900 (664,862 to 676,938) km.
- Type: satellite
- Europa hosts a number of Unified Government mining bases (for water, among other minerals).
- Europa Base 7 (Isamu Alva Dyson assigned here, 2038.02.09)
Ganymede is the largest moon of Jupiter and in the Solar System, and the only moon known to have a magnetosphere. Ganymede participates in a 1:2:4 orbital resonance with the moons Europa and Io, respectively. Ganymede is composed of approximately equal amounts of silicate rock and water ice. It is a fully differentiated body with an iron-rich, liquid core, and an internal ocean that may contain more water than all of Earth's oceans together.
Ganymede's magnetosphere was probably created through convection within its liquid iron core. The meager magnetosphere is buried within Jupiter's much larger magnetic field, and would show only as a local perturbation of the field lines. The satellite has a thin oxygen atmosphere that includes O, O2, and possibly O3 (ozone).
- Size: 5,268.2+/-0.6 km
- Orbital period of 7.15 days at a distance of 1.070 (1.069 to 1.071)Gm.
- Type: satellite
- Unified Government water and mining colony.
Callisto's rotation is tidally locked to its orbit around Jupiter, so that the same hemisphere always faces inward. It is less affected by Jupiter's magnetosphere because it is located just outside Jupiter's main radiation belt. Because of its low radiation levels, Callisto has long been considered the most suitable place for a human base for future exploration of the Jovian system.
Callisto is composed of approximately equal amounts of rock and ices. Callisto may have a small silicate core and possibly a subsurface ocean of liquid water at depths greater than 100 km. At a small scale, the surface is varied and made up of small, sparkly frost deposits at the tips of high spots, surrounded by a low-lying, smooth blanket of dark material. Callisto is surrounded by an extremely thin atmosphere composed of carbon dioxide and probably molecular oxygen, as well as by a rather intense ionosphere.
The likely presence of an ocean within Callisto leaves open the possibility that it could harbor life. However, conditions are thought to be less favorable than on nearby Europa.
- Size: 4,821 km
- Orbital period of 16.7 days at a distance of 1.88 (1.87 to 1.90) Gm.
- Type: satellite
Magnetosphere Bow Shock
Jupiter's magnetosphere is a complex structure comprising a bow shock, magnetosheath, magnetopause, magnetotail, magnetodisk, and other components. The magnetic field around Jupiter emanates from a number of different sources, including fluid circulation at the planet's core (the internal field), electrical currents in the plasma surrounding Jupiter, and the currents flowing at the boundary of the planet's magnetosphere. The magnetosphere is embedded within the plasma of the solar wind, which carries the interplanetary magnetic field.
The Jovian magnetosphere is so large that the Sun and its visible corona would fit inside it with room to spare. At the opposite side of the planet, the solar wind stretches Jupiter's magnetic field lines into a long, trailing magnetotail, which sometimes extends well beyond the orbit of Saturn. The structure of Jupiter's magnetotail consists of two lobes, with the magnetic field in the southern lobe pointing toward Jupiter, and that in the northern lobe pointing away from it. The lobes are separated by a thin layer of plasma called the tail current sheet. The Jovian tail is a channel through which solar plasma enters the inner regions of the magnetosphere, where it is heated and forms the radiation belts at distances closer than 0.699 Gm from Jupiter.
- Bow shock: ~5.73 Gm from Jupiter
Themisto
Themisto's orbit is unusual: unlike most of Jupiter's moons, which orbit in distinct groups, Themisto orbits alone. The moon is located midway between the Galilean moons and the first group of prograde irregular moons.
- Size: 8 km
- Orbital period of 129.8 days at a distance of 7.39 (5.91 to 8.87) Gm.
- Type: irregular satellite
Himalia group
A group of prograde irregular satellites of Jupiter that follow similar orbits to Himalia and are thought to have a common origin. In physical appearance, the group is very homogenous, all satellites displaying neutral colours, similar to those of C-type asteroids. Given the limited dispersion of the orbital parameters and the spectral homogeneity, it has been suggested that the group could be a remnant of the break-up of an asteroid from the main asteroid belt.
The known members of the group are (in order of increasing distance from Jupiter):
- Leda: 28 km size; orbital period of 240.9 days at a distance of 11.2 Gm.
- Himalia: 170+/-? km size; orbital period of 250.6 days at a distance of 11.5 Gm.
- Lysithea: 36 km size; orbital period of 259.2 days at a distance of 11.7 Gm.
- Elara: 86 km size; orbital period of 259.6 days at a distance of 11.7 Gm.
- Dia: ≈4 km size; orbital period of 274 days at a distance of 12.1 Gm.
Carpo
All of the moons further from Jupiter than Carpo are retrograde.
- Size: ~3.0 km
- Orbital period of 1.26 years at a distance of 17.1 Gm.
- Type: irregular satellite
S/2003 J 12
The smallest known satellite in the Solar System.
- Size: ~1.0 km
- Orbital period of 1.34 years at a distance of 17.9 Gm.
- Type: irregular retrograde satellite
Ananke group
The Ananke group is a group of retrograde irregular satellites of Jupiter that follow similar orbits to Ananke and are thought to have a common origin. Their semi-major axes (distances from Jupiter) range between 19.3 and 22.7 Gm, their orbital inclinations between 145.7° and 154.8°, and their orbital eccentricities between 0.02 and 0.28. The Ananke group is believed to have been formed when an asteroid was captured by Jupiter and subsequently fragmented by a collision.
Core members include, from largest to smallest:
- Ananke: 28 km size; orbital period of 1.68 years at a distance of 21.3 Gm.
- Praxidike: 7 km size; orbital period of 1.68 years at a distance of 20.1 Gm.
- Iocaste: 5.2 km size; orbital period of 1.67 years at a distance of 21.2 Gm.
- Harpalyke: 4 km size; orbital period of 1.71 years at a distance of 21.1 Gm.
- Thyone: 4 km size; orbital period of 1.75 years at a distance of 21.4 Gm.
- Euanthe: 3 km size; orbital period of 1.64 years at a distance of 20.5 Gm.
- Euporie: 2 km size; orbital period of 1.48 years at a distance of 19.1 Gm.
Carme group
The Carme group is a group of retrograde irregular satellites of Jupiter that follow similar orbits to Carme and are thought to have a common origin. Their semi-major axes range between 22.9 and 24.1 Gm, their orbital inclinations between 164.9° and 165.5°, and their orbital eccentricities between 0.23 and 0.27. The very low dispersion among the core members suggests that the Carme group may once have been a single body that was broken apart by an impact.
Core members include (from largest to smallest):
- Carme: ~46 km size; orbital period of 1.92 years at a distance of 23.4 Gm.
- Taygete: 5 km size; orbital period of 1.88 years at a distance of 22.4 Gm.
- Eukelade: 4 km size; orbital period of 2.01 years at a distance of 23.5 Gm.
- S/2003 J 5: 4 km size; orbital period of 2.08 years at a distance of 24.0 Gm.
- Chaldene: 3.8 km size; orbital period of 1.91 years at a distance of 23.8 Gm.
- Isonoe: 3.8 km size; orbital period of 2.06 years at a distance of 23.2 Gm.
- Kalyke: 5.2 km size; orbital period of 1.97 years at a distance of 23.2 Gm. Substantially redder than the others.
- Erinome: 3.2 km size; orbital period of 1.95 years at a distance of 23.0 Gm.
- Aitne: 3 km size; orbital period of 1.86 years at a distance of 22.3 Gm.
- Kale: 2 km size; orbital period of 1.88 years at a distance of 22.4 Gm.
- Pasithee: 2 km size; orbital period of 1.99 years at a distance of 23.3 Gm.
- S/2003 J 9: 1 km size; orbital period of 2.06 years at a distance of 23.9 Gm.
- S/2003 J 10: 2 km size; orbital period of 1.92 years at a distance of 22.7 Gm.
Pasiphaë Group
A group of retrograde irregular satellites of Jupiter that follow similar orbits to Pasiphaë, and are thought to have a common origin. Their semi-major axes range between 22.8 and 24.1 Gm (the same range as the Carme group), their inclinations between 144.5° and 158.3°, and their eccentricities between 0.25 and 0.43. The Pasiphaë group is believed to have been formed when Jupiter captured an asteroid, which subsequently broke up after a collision.
Core members include (from largest to smallest):
- Pasiphaë: 58 km size; orbital period of 2.09 years at a distance of 24.1 Gm.
- Sinope: ~38 km size; orbital period of 1.95 years at a distance of 23.5 Gm.
- Callirrhoe: ~17.2 km size; orbital period of 2.1 years at a distance of 24.1 Gm.
- Megaclite: 5.4 km size; orbital period of 2.17 years at a distance of 24.7 Gm.
- Autonoe: 4 km size; orbital period of 2.11 years at a distance of 24.3 Gm.
- Eurydome: 3 km size; orbital period of 1.98 years at a distance of 23.2 Gm.
- Sponde: 2 km size; orbital period of 2.11 years at a distance of 24.3 Gm.
S/2003 J 2
It seems to belong to a group all of its own, with an inclination of ~160°.
- Size: 2 km
- Orbital period of 981.6 years at a distance of 29.54 Gm.
- Type: retrograde irregular satellite
The Jupiter trojans, commonly called Trojan asteroids or just Trojans, are a large group of objects that share the orbit of the planet Jupiter around the Sun. Relative to Jupiter, each trojan librates around one of Jupiter's two stable Lagrangian points. Jupiter trojans are distributed in two elongated, curved regions around these Lagrangian points, with an average semi-major axis of about 5.2 AU.
The total number of Jupiter trojans larger than 1 km in diameter is believed to be about 1 million. Like main-belt asteroids, Jupiter trojans form families. Jupiter trojans are dark bodies with reddish, featureless spectra.
- Greek Camp
Orbits the L4 Lagrangian point of the Sun-Jupiter system, about 60° ahead Jupiter. The following are a selection of the largest in the Greek Camp:
- Hektor: 226.68+/-15.15 km size; orbital period of 11.93 years at a distance of 5.22 (5.10 to 5.35) AU.
The largest Jupiter trojan. It is a D-type asteroid, dark and reddish in colour. Hektor is one of the most elongated bodies of its size in the Solar System, being 370x200 km. It is thought that Hektor might be a contact binary.
- S/2006 (624) 1: 12 km size; orbital period of 3.00 days at a distance of 623.5 km.
- Agamemnon: 167 km size; orbital period of 11.91 years at a distance of 5.21 (4.86 to 5.57) AU. Located in the leading Lagrangian point L4. Recent observations of the asteroid's occultations are suggestive of Agamemnon to have a satellite.
- Diomedes: 164.3+/-4.1 km size; orbital period of 11.74 years at a distance of 5.16 (4.94 to 5.39) AU.
- Achilles: 135.5 km size; orbital period of 11.83 years at a distance of 5.19 (4.43 to 5.96) AU.
- Odysseus: 126 km size; orbital period of 12.03 years at a distance of 5.25 (4.77 to 5.73) AU. As a Jupiter Trojan, it is in a very stable orbit.
- Trojan Camp
Orbits the L5 Lagrangian point of the Sun-Jupiter system, about 60° behind Jupiter. The following are a selection of the largest in the Trojan Camp:
- Patroclus: 143.14+/-8.37 km size; orbital period of 11.92 years at a distance of 5.22 (4.49 to 5.95) AU.
A binary minor planet made up of two objects of similar size orbiting their common centre of gravity. Recent evidence suggests that the objects are icy like comets, rather than rocky like most asteroids.
- Menoetius: 112 km size; orbital period of 4.28 days at a distance of 680+/-20 km
- Äneas: 143 km size; orbital period of 11.88 years at a distance of 5.21 (4.66 to 5.76) AU.
- Anchises: 126 km size; orbital period of 12.22 years at a distance of 5.31 (4.57 to 6.04) AU. A dark P-type asteroid.
Centaurs are small Solar System bodies with a semi-major axis between those of the outer planets. They have unstable orbits that cross or have crossed the orbits of one or more of the giant planets, and have dynamic lifetimes of a few million years. Centaurs typically behave with characteristics of both asteroids and comets.
No centaur has been photographed up close, although there is evidence that Saturn's moon Phoebe may be a captured centaur. As of 2008, three centaurs have been found to display cometary comas: Chiron, 60558 Echeclus, and 166P/NEAT. Chiron and Echeclus are therefore classified as both asteroids and comets. Other centaurs, such as 52872 Okyrhoe, are suspected of showing cometary activity. Any centaur that is perturbed close enough to the Sun is expected to become a comet.
The comet is unusual in that it suddenly undergoes an outburst. This causes the comet to brighten by 1 to 4 magnitudes. This happens with a frequency of 7.3 outbursts per year, fading within a week or two. The magnitude of the comet has been known to vary from 19th magnitude to 9th magnitude, a ten thousand-fold increase in brightness, during its brightest outbursts.
- Size: est 30.8 km
- Orbital period of 14.65 years at a distance of 5.98 (5.72 to 6.25) AU.
- Type: Periodic comet, Centaur.
Of objects listed as a centaur, Okyrhoe has the second smallest perihelion distance of a numbered centaur.
- Size: 49 km
- Orbital period of 24.20 years at a distance of 8.37 (5.80 to 10.93) AU.
- Type: Centaur.
Of numbered objects listed as a centaur, 2008 QD
4 has the smallest perihelion distance.
- Size: 31 km
- Orbital period of 24.46 years at a distance of 8.43 (5.44 to 11.41) AU.
- Type: Centaur.
Saturn is a gas giant. Its interior is probably composed of a core of iron-nickel and rock (silicon and oxygen compounds). This core is surrounded by a deep layer of metallic hydrogen, an intermediate layer of liquid hydrogen and liquid helium, and finally outside the Frenkel line, a gaseous outer layer. Saturn has a pale yellow hue due to ammonia crystals in its upper atmosphere. Electrical current within the metallic hydrogen layer is thought to give rise to Saturn's planetary magnetic field. Saturn's magnetic field strength is around one-twentieth the strength of Jupiter's. The outer atmosphere is generally bland and lacking in contrast, although long-lived features can appear. Wind speeds on Saturn can reach 1,800 kmph, faster than on Jupiter, but not as fast as those on Neptune.
Saturn has a prominent ring system that consists of nine continuous main rings and three discontinuous arcs, and that is composed mostly of ice particles, with a smaller amount of rocky debris and dust. Sixty-two moons are known to orbit Saturn, of which fifty-three are officially named. This does not include the hundreds of moonlets comprising the rings. Titan is larger than the planet Mercury, and is the only moon in the Solar System to have a substantial atmosphere.
- Size: 116,464+/-12 km
- Orbital period of 29.46 years at a distance of 9.58 (9.05 to 10.12) AU.
- Type: planet
- Orbit:
- Reds Wood Satellite City
D Ring
The innermost ring, and is very faint. Three ringlets, designated D73, D72 and D68, were detected within this ring in 1980, with D68 being the discrete ringlet nearest to Saturn. Some 25 years later, D72 had become significantly broader and more diffuse, and had moved planetward by 200 km.
- 66,900-74,510 km from Saturn
- Width: 7,500 km
- Depth: 5 m
C Ring
A wide, but faint ring.
- 74,658-92,000 km from Saturn
- Width: 17,500 km
- Depth: 5 m
- Colombo Gap and Titan Ringlet: 150 km wide, located 77,870 km from Saturn. Within the gap lies the bright but narrow Titan Ringlet (=25 km wide, centered at 77,883 km from Saturn), which is slightly elliptical rather than circular.
- Maxwell Gap and Ringlet: 270 km wide, located 87,491 km from Saturn. It also contains a dense non-circular ringlet, the Maxwell Ringlet (=64 km wide, centered at 87,491 km from Saturn).
- Bond Gap: 30 km wide, located 88,705 km from Saturn.
- 1.470RS Ringlet: 16 km wide gap located 88,716 km from Saturn.
- 1.495RS Ringlet: 62 km wide, located 90,171 km km from Saturn.
- Dawes Gap: 20 km wide, located 90,210 km from Saturn.
B Ring
The largest, brightest, and most massive of the rings. The B Ring contains a great deal of variation in its density and brightness, nearly all of it unexplained. These are concentric, appearing as narrow ringlets, though the B Ring does not contain any gaps. In places, the outer edge of the B Ring contains vertical structures deviating up to 2.5 km from the main ring plane.
- 92,000-117,580 km from Saturn
- Width: 25,500 km
- Depth: 5 to 15 m
S/2009 S 1
A 'propeller moonlet' of Saturn orbiting in the outer part of Saturn's B Ring.
- Size: approx. 400 m
- Orbital period of 0.47 days at a distance of 117,000 km.
- Type: satellite
Cassini Division
The gap is populated by ring material bearing much similarity to the C Ring. The ring particles in the inner edge of the Cassini Division orbit twice for every orbit of the moon Mimas. The resonance causes Mimas' pulls on these ring particles to accumulate, destabilizing their orbits and leading to a sharp cutoff in ring density.
- 117,580-122,170 km from Saturn
- Width: 4,700 km
- Depth: 5 to 15 m
- Huygens Gap: 285-400 km wide, located 133,589 km from Saturn. It contains the dense, eccentric Huygens Ringlet (=17 km wide, 117,848 km from Saturn) in the middle. This ringlet exhibits irregular azimuthal variations of geometrical width and optical depth, which may be caused by the nearby 2:1 resonance with Mimas and the influence of the eccentric outer edge of the B-ring. There is an additional narrow ringlet just outside the Huygens Ringlet.
- Herschel Gap: 102 km wide, located 118,234 km from Saturn.
- Russell Gap: 33 km wide, located 118,614 km from Saturn.
- Jeffreys Gap: 38 km wide gap located 118,950 km from Saturn.
- Kuiper Gap: 3 km wide, located 119,405 km from Saturn.
- Laplace Gap: 238 km wide, located 119,967 km from Saturn.
- Bessel Gap: 10 km wide, located 120,241 km from Saturn.
- Barnard Gap: 13 km wide, located 120,312 km from Saturn.
A Ring
The A Ring's inner boundary is the Cassini Division, and its sharp outer boundary is close to the orbit of the small moon Atlas. The A Ring is interrupted at a location 22% of the ring width from its outer edge by the Encke Gap. A narrower gap, 2% of the ring width from the outer edge, is called the Keeler Gap. The A Ring's outer edge is maintained by a 7:6 resonance with Janus and Epimetheus. Other orbital resonances also excite many spiral density waves in the A Ring, which account for most of its structure.
- 122,170-136,775 km from Saturn
- Width: 14,600 km
- Depth: 10 to 30 m
- Encke Gap: 325 km wide, located 133,589 km from Saturn. Caused by the presence of the small moon Pan, which orbits within it. There are at least three thin, knotted ringlets within the gap. Spiral density waves visible on both sides of it are induced by resonances with nearby moons exterior to the rings, while Pan induces an additional set of spiraling wakes.
- Keeler Gap: 35 km wide, located 136,505 km from Saturn. The small moon Daphnis orbits within it, keeping it clear. The moon induces waves in the edges of the gap. Because the orbit of Daphnis is slightly inclined to the ring plane, the waves have a component that is perpendicular to the ring plane, reaching a distance of 1.5 km "above" the plane.
Propeller Moonlets
The moonlets themselves are tiny, ranging from about 40 to 500 meters in diameter, and are too small to be seen directly. They are confined to three narrow bands in the A Ring between 126,750 and 132,000 km from Saturn's center. Each band is about 1,000 km wide, which is less than 1% the width of Saturn's rings.
The moonlets were probably formed from the breakup of a larger satellite. It is estimated that the A Ring contains 7,000-8,000 propellers larger than 0.8 km in size, and millions larger than 0.25 km.
Pan
Pan is a walnut-shaped small moon, that orbits within the Encke Gap in Saturn's A Ring. Pan acts as a ring shepherd and is responsible for keeping the Encke Gap free of ring particles. It has an equatorial ridge, similar to that on Atlas. The ridge is due to ring material that Pan has swept up from the Encke gap.
- Size: 28.2+/-2.6 km
- Orbital period of 0.58 days at a distance of 133,584 km.
- Type: satellite
Daphnis
Daphnis orbits the planet in the Keeler Gap within the A ring. Before it was photographed, the existence of a moon in Daphnis's position had already been inferred from gravitational ripples observed on the outer edge of the Keeler gap. The waves made by the moon in the inner edge of the gap precede it in orbit, while those on the outer edge lag behind it, due to the differences in relative orbital speed.
- Size: 7.6+/-1.6 km
- Orbital period of 0.59 days at a distance of 136,505.5 km.
- Type: satellite
Roche Division
Lying at the outer edge of the main ring system, the Roche Division is in fact close to Saturn's Roche limit, which is why the rings have been unable to accrete into a moon. The Roche Division is not empty but contains a sheet of material. The character of this material is similar to the tenuous and dusty D, E, and G Rings. Two locations in the Roche Division have a higher concentration of dust than the rest of the region.
- 136,775-139,380 km from Saturn
- Width: 2,600 km
- Depth: 10-1,000 m
- R/2004 S 1: located along the orbit of the moon Atlas.
- R/2004 S 2: centered at 138,900 km from Saturn, inward of the orbit of Prometheus.
Atlas
Atlas has a roughly spherical centre surrounded by a large, smooth equatorial ridge. The most likely explanation for this unusual and prominent structure is that ring material swept up by the moon accumulates on the moon, with a strong preference for the equator due to the ring's thinness. In fact, the size of the equatorial ridge is comparable with the expected Roche lobe of the moon.
Atlas is significantly perturbed by Prometheus and to a lesser degree by Pandora, leading to excursions in longitude of up to 600 km away from the precessing Keplerian orbit with a rough period of about 3 years. Since the orbits of Prometheus and Pandora are chaotic, it is suspected that Atlas's may be as well.
- Size: 30.2+/-1.8 km
- Orbital period of 0.60 days at a distance of 137,670 km.
- Type: satellite
Prometheus
Prometheus is extremely elongated. It has several ridges and valleys and a number of impact craters of about 20 km diameter are visible, but it is less cratered than nearby Pandora, Epimetheus and Janus. It seems likely that Prometheus is a very porous icy body. Prometheus acts as a shepherd satellite for the inner edge of Saturn's narrow F Ring.
The orbit of Prometheus appears to be chaotic, as a consequence of a series of four 121:118 mean-motion resonances with Pandora. The most appreciable changes in their orbits occur approximately every 6.2 years, when the periapsis of Pandora lines up with the apoapsis of Prometheus and the moons approach to within about 1,400 km. Prometheus is itself a significant perturber of Atlas, with which it is in a 53:54 mean-longitude resonance.
- Size: 86.2+/-5.4 km
- Orbital period of 0.61 days at a distance of 139,380 km.
- Type: satellite
F Ring
The outermost discrete ring of Saturn, and perhaps the most active ring in the Solar System, with features changing on a timescale of hours. The F Ring consists of one core ring and a spiral strand around it. When Prometheus encounters the ring at its apoapsis, its gravitational attraction creates kinks and knots in the F Ring as the moon 'steals' material from it, leaving a dark channel in the inner part of the ring. Since Prometheus orbits Saturn more rapidly than the material in the F ring, each new channel is carved about 3.2° in front of the previous one.
- 140,180 km from Saturn
- Width: 30-500 km
- Depth: 10-1,000 m
Janus/Epimetheus Ring
A faint dust ring is present around the region occupied by the orbits of Janus and Epimetheus.
- 149,000-154,000 km from Saturn
- Width: 5,000 km
- Depth: 10-1,000 m
Epimetheus
Epimetheus occupies essentially the same orbit as the moon Janus. The moons "trade" orbits, never approaching closer than about 10,000 km. The exchange takes place about once every four years. There are several Epimethean craters larger than 30 km in diameter, as well as both large and small ridges and grooves. It seems likely that Epimetheus is a very porous icy body.
- Size: 116.2+/-3.6 km
- Orbital period of 0.69 days at a distance of 151,410 km.
- Type: satellite
Janus
Janus occupies practically the same orbit as the moon Epimetheus. Janus is extensively cratered with several craters larger than 30 km but few linear features. The Janian surface appears to be older than Prometheus's but younger than Pandora's. It seems likely that Janus is a very porous and icy rubble pile. The moon is also highly non-spherical. Along with Ephimetheus, Janus maintains the sharp edge of the A Ring by a 7:6 orbital resonance.
- Size: 179+/-2.8 km
- Orbital period of 0.69 days at a distance of 151,460 km.
- Type: satellite
G Ring
The G Ring is a very thin, faint ring. It contains a single distinctly brighter arc near its inner edge that extends about one sixth of its circumference, centered on the half-kilometre diameter moonlet Aegaeon. The arc is believed to be composed of icy particles up to a few metres in diameter, with the rest of the G Ring consisting of dust released from within the arc. The radial width of the arc is about 250 km.
- 166,000-175,000 km from Saturn
- Width: 9,000 km
- Depth: 10-1,000 m
Aegaeon
Aegaeon is thought to be similarly smooth as Methone. Aegaeon orbits within the bright segment of Saturn's G Ring, and is probably a major source of the ring. Debris knocked off Aegaeon forms a bright arc near the inner edge, which in turn spreads to form the rest of the ring. Aegaeon orbits in a 7:6 corotation eccentricity resonance with Mimas, which causes an approximately 4-year oscillation of about 4 km in its semi-major axis, and a corresponding oscillation of a few degrees in its mean longitude.
- Size: 500 m
- Orbital period of 0.81 days at a distance of 167,494 km.
- Type: satellite
Mimas is composed mostly of water ice with only a small amount of rock. Due to the tidal forces acting on it, Mimas 's longest axis is about 10% longer than the shortest. The giant impact crater Herschel is 130 km across -almost a third of Mimas's own diameter; its walls are approximately 5 km high, parts of its floor measure 10 km deep, and its central peak rises 6 km above the crater floor. The impact that made this crater must have nearly shattered Mimas: fractures can be seen on the opposite side of Mimas that may have been created by shock waves from the impact travelling through Mimas's body.
Mimas is responsible for clearing the material from the Cassini Division. Particles in the Huygens Gap at the inner edge of the Cassini division are in a 2:1 resonance with Mimas. The boundary between the C and B ring is in a 3:1 resonance with Mimas. Recently, the G Ring was found to be in a 7:6 co-rotation eccentricity resonance with Mimas; the ring's inner edge is about 15,000 km inside Mimas's orbit. Mimas is also in a 2:1 mean-motion resonance with the larger moon Tethys, and in a 2:3 resonance with the outer F Ring shepherd moonlet, Pandora.
- Size: 396.4+/-0.8 km
- Orbital period of 0.94 days at a distance of 185,539 (181,902 to 189,176) km.
- Type: satellite
Methone Ring Arc
A faint ring arc, covering a longitudinal extent of about 10°, is associated with the moon Methone. The material in the arc is believed to represent dust ejected from Methone by micrometeoroid impacts. The confinement of the dust within the arc is attributable to a 14:15 resonance with Mimas.
- 194,230 km from Saturn
- Width: ? km
- Depth: ? m
Methone
Methone's orbit is visibly affected by a perturbing 14:15 mean-longitude resonance with the much larger Mimas. This causes its osculating orbital elements to vary. It is an egg-shaped moonlet with a remarkably smooth surface, with no visible craters. It is suggested that Methone is composed of icy fluff, material that might be mobile enough to explain the lack of craters.
- Size: 3.2+/-1.2 km
- Orbital period of 1.01 days at a distance of 194,440 km.
- Type: satellite
Anthe Ring Arc
A faint ring arc, covering a longitudinal extent of about 20°, is associated with the moon Anthe. The material in the arc is believed to represent dust knocked off Anthe by micrometeoroid impacts. The confinement of the dust within the arc is attributable to a 10:11 resonance with Mimas.
- 197,665 km from Saturn
- Width: ? km
- Depth: ? m
Anthe
Anthe is visibly affected by a perturbing 10:11 mean-longitude resonance with the much larger Mimas. This causes its osculating orbital elements to vary with an amplitude of about 20 km in semi-major axis on a timescale of about 2 Earth years. The close proximity to the orbits of Pallene and Methone suggests that these moons may form a dynamical family.
- Size: ~1 km
- Orbital period of 1.04 days at a distance of 197,700 km.
- Type: satellite
Pallene Ring
A faint dust ring. Its source is particles blasted off Pallene's surface by meteoroid impacts, which then form a diffuse ring around its orbital path.
- 211,000-213,500 km from Saturn
- Width: 2,500 km
- Depth: 10-1,000 m
Pallene
One of three small moons, known as the Alkyonides, that lie between the orbits of the larger Mimas and Enceladus. Pallene is visibly affected by a perturbing mean-longitude resonance with the much larger Enceladus The perturbations cause Pallene's osculating orbital elements to vary.
- Size: 5.0+/-1.2 km
- Orbital period of 1.15 days at a distance of 212,280 km.
- Type: satellite
E Ring
The E Ring is extremely wide, distributed between the orbits of Mimas and Titan. Unlike the other rings, it is composed of microscopic particles rather than macroscopic ice chunks. The source of the material is the cryovolcanic plumes of the moon Enceladus. Unlike the main rings, the E Ring increases in thickness with its distance from Enceladus. Tendril-like structures observed within the E Ring can be related to the emissions of the most active south polar jets of Enceladus.
- 180,000-480,000 km from Saturn
- Width: 300,000 km
- Depth: 2,000 km
Enceladus is mostly covered by fresh, clean ice and the surface temperature at noon only reaches -198°C. Enceladus has a wide range of surface features ranging from old, heavily cratered regions to young, tectonically deformed terrains that formed as recently as 100 million years ago, despite its small size.
Cryovolcanoes near the south pole shoot geyser-like jets of water vapor, other volatiles, and solid material, including sodium chloride crystals and ice particles, into space, totaling approximately 200 kg per second. Over 100 geysers have been identified. Some of the water vapor falls back as "snow"; the rest escapes, and supplies most of the material making up Saturn's E ring. The plumes at Enceladus seem similar in chemical makeup to comets. There is evidence of a large south polar subsurface ocean of liquid water within Enceladus with a thickness of around 10 km.
These geyser observations, along with the finding of escaping internal heat and very few (if any) impact craters in the south polar region, show that Enceladus is geologically active today. Enceladus is, like many satellites in the extensive systems of giant planets, trapped in an orbital resonance. Its resonance with Dione excites its orbital eccentricity, which tidal forces damp, resulting in tidal heating of its interior.
- Size: 504.2+/-0.4 km
- Orbital period of 1.37 days at a distance of 237,948 km.
- Type: satellite
Tethys has a low density, the lowest of all the major moons in the Solar System, indicating that it is made of water ice with just a small fraction of rock. Tethys is heavily cratered and cut by a number of large faults/graben. The largest impact crater, Odysseus, is about 400 km in diameter, whereas the largest graben, Ithaca Chasma, is about 100 km wide and more than 2,000 km long. These two largest surface features may be related. A small part of the surface is covered by smooth plains that may be cryovolcanic in origin. Tethys formed from the Saturnian sub-nebula -a disk of gas and dust that surrounded Saturn soon after its formation.
- Size: 1,062.2+/-1.2 km
- Orbital period of 1.89 days at a distance of 294,619 km.
- Type: satellite
- Saturn-Tethys Lagrangian points
- L4:
Telesto
Its surface is surprisingly smooth, devoid of small impact craters.
- Size: 24.8+/-0.8 km
- Orbital period of 1.89 days at a distance of 294,619 km.
- Type: satellite; co-orbital with Tethys
- L5:
Calypso
Calypso is irregularly shaped, has overlapping large craters, and appears to also have loose surface material capable of smoothing the craters' appearance.
- Size: 21.4+/-1.4 km
- Orbital period of 1.89 days at a distance of 294,619 km.
- Type: satellite; co-orbital with Tethys
Dione is currently in a 1:2 mean-motion orbital resonance with moon Enceladus, completing one orbit of Saturn for every two orbits completed by Enceladus. This resonance maintains Enceladus's orbital eccentricity, providing a source of heat for Enceladus's extensive geological activity, which shows up most dramatically in its cryovolcanic geyser-like jets.
Dione is composed primarily of water ice, but it must have a considerable fraction (~46%) of denser material like silicate rock in its interior. Dione's leading hemisphere is heavily cratered and is uniformly bright. Its trailing hemisphere, however, contains an unusual and distinctive surface feature: a network of bright ice cliffs. Like Callisto, Dione's craters lack the high-relief features seen on the Moon and Mercury; this is probably due to slumping of the weak icy crust over geologic time.
- Size: 1,122.8+/-0.8 km
- Orbital period of 2.74 days at a distance of 377,396 km.
- Type: satellite
- Saturn-Dione Lagrangian points
- L4:
Helene
A co-orbital with Dione and located in its leading Lagrangian point (L4). It is one of four known trojan moons.
- Size: 35.2+/-0.8 km
- Orbital period of 2.74 days at a distance of 377,396 km.
- Type: satellite; co-orbital with Dione
- L5:
Polydeuces
A co-orbital with Dione and librates around its trailing Lagrangian point (L5). Of the four known Lagrangian co-orbitals in the Saturn system, Polydeuces wanders the farthest from its Lagrangian point: its distance behind Dione varies from 33.9° to 91.4° with a period of 790.931 days (for comparison, L5 trails Dione by 60°).
- Size: 2.6+/-0.8 km
- Orbital period of 2.74 days at a distance of 377,396 km.
- Type: satellite; co-orbital with Dione
It is the smallest body in the Solar System confirmed to be in hydrostatic equilibrium. Rhea is an icy body with a low density, which indicates that it is made of ~25% rock and ~75% water ice. Models suggest that Rhea could be capable of sustaining an internal liquid-water ocean through heating by radioactive decay.
It has a tenuous atmosphere - an exosphere. It consists of oxygen and carbon dioxide in proportion of roughly 5 to 2. The main source of oxygen is radiolysis of water ice at the surface by ions supplied by the magnetosphere of Saturn. The source of the carbon dioxide is less clear, but it may be related to oxidation of the organics present in ice or to outgassing of the moon's interior.
Rhea may have a tenuous ring system consisting of three narrow, relatively dense bands within a particulate disk. This would be the first discovery of rings around a moon.
- Size: 1,527.6+/-2.0 km
- Orbital period of 4.52 days at a distance of 527,108 km.
- Type: satellite
Titan is the only natural satellite known to have a dense atmosphere, and the only object other than Earth where clear evidence of stable bodies of surface liquid has been found. Frequently described as a planet-like moon, Titan's diameter is 50% larger than Earth's natural satellite, the Moon, and it is 80% more massive. Titan is primarily composed of water ice and rocky material. The geologically young surface is generally smooth, with few impact craters, although mountains and several possible cryovolcanoes have been found.
The atmosphere of Titan is largely nitrogen; minor components lead to the formation of methane and ethane clouds and nitrogen-rich organic smog. The climate-including wind and rain- creates surface features similar to those of Earth, such as dunes, rivers, lakes, seas (probably of liquid methane and ethane), and deltas, and is dominated by seasonal weather patterns as on Earth. With its liquids (both surface and subsurface) and robust nitrogen atmosphere, Titan's methane cycle is viewed as an analogy to Earth's water cycle, although at a much lower temperature.
- Size: 5,152+/-4.0 km
- Orbital period of 15.95 days at a distance of 1.22 (1.19 to 1,26) Gm.
- Type: satellite
Hyperion is distinguished by its irregular shape, its chaotic rotation, and its unexplained sponge-like appearance. The largest crater on Hyperion is approximately 121.57 km in diameter and 10.2 km deep. A possible explanation for the irregular shape is that Hyperion is a fragment of a larger body that was broken up by a large impact in the distant past.
Hyperion's low density indicates that it is composed largely of water ice with only a small amount of rock. It is thought that Hyperion may be similar to a loosely accreted pile of rubble in its physical composition. Hyperion is redder than Phoebe and closely matches the color of the dark material on Iapetus.
- Size: 270 km
- Orbital period of 21.27 days at a distance of 1,48 Gm.
- Type: satellite
It is the largest body in the Solar System known not to be in hydrostatic equilibrium. Iapetus is best known for its dramatic 'two-tone' coloration. The low density of Iapetus indicates that it is mostly composed of ice, with only a small (~20%) amount of rocky materials. Unlike most of the large moons, its overall shape is neither spherical nor ellipsoid, but has a bulging waistline and squashed poles; also, its unique equatorial ridge is so high that it visibly distorts Iapetus's shape even when viewed from a distance. These features often lead it to be characterized as walnut-shaped.
Iapetus is heavily cratered with large impact basins, at least five of which are over 350 km wide. The largest, Turgis, has a diameter of 580 km; its rim is extremely steep and includes a scarp about 15 km high. Iapetus is known to support long-runout landslides or sturzstroms, possibly supported by ice sliding.
- Size: 1,469+/-5.6 km
- Orbital period of 79.32 days at a distance of 3.56 Gm.
- Type: satellite
Magnetosphere Bow Shock
Saturn's internal magnetic field deflects the solar wind, instead creating its own region, called a magnetosphere, composed of a plasma very different from that of the solar wind. The boundary separating the solar wind's plasma from that within Saturn's magnetosphere is called the magnetopause. In front of Saturn's magnetopause lies the bow shock, a wake-like disturbance in the solar wind caused by its collision with the magnetosphere. The region between the bow shock and magnetopause is called the magnetosheath. At the opposite side of the planet, the solar wind stretches Saturn's magnetic field lines into a long, trailing magnetotail, which consists of two lobes, with the magnetic field in the northern lobe pointing away from Saturn and the southern pointing towards it. The lobes are separated by a thin layer of plasma called the tail current sheet. Saturn's tail is a channel through which solar plasma enters the inner regions of the magnetosphere. The plasma moving from the tail to the inner magnitopshere is heated and forms a number of radiation belts.
- Bow shock: 1.63 Gm from Saturn
- Phoebe ring
A tenuous disk of material just interior to the orbit of Phoebe. Although very large, the ring is virtually invisible. Ring material migrates inward. The material would thus strike the leading hemisphere of Iapetus. Infall of this material causes a slight darkening and reddening of the leading hemisphere of Iapetus but does not directly create the dramatic two-tone coloration of that moon.
- 4.0-13.0 Gm from Saturn
- Width: 9.0 Gm
- Depth: 2,329 km
Inuit group
A dynamical grouping of the prograde irregular satellites Saturn which follow similar orbits. The satellites displaying light-red colour. Ijiraq is distinctively redder than Paaliaq, Siarnaq and Kiviuq. The spectral homogeneity (with the exception of Ijiraq) is consistent with a common origin in the break-up of a single object.
- Kiviuq: 16 km size; orbital period of 1.23 years at a distance of 11.11 Gm.
- Ijiraq: 12 km size; orbital period of 1.24 years at a distance of 11.12 Gm.
- Paaliaq: 22 km size; orbital period of 1.88 years at a distance of 15.20 Gm.
- Siarnaq: 40 km size; orbital period of 2.45 years at a distance of 17.53 Gm.
- Tarqeq: 7 km size; orbital period of 2.45 years at a distance of 17.91 Gm.
Gallic group
A dynamical grouping of the prograde irregular satellites of Saturn following similar orbits. The group was later found to be physically homogeneous, all satellites displaying light-red colour. Observations revealed that the largest member of the group, Albiorix, actually displays two different colours: one compatible with Erriapus and Tarvos, and another less red. It was postulated that Tarvos and Erriapus could be fragments of Albiorix, leaving a large, less red crater.
- Albiorix: 32 km size; orbital period of 2.15 years at a distance of 16.18 Gm.
- Bebhionn: 6 km size; orbital period of 2.25 years at a distance of 17.34 Gm.
- Erriapus: 10 km size; orbital period of 2.38 years at a distance of 18.36 Gm.
- Tarvos: 15 km size; orbital period of 2.63 years at a distance of 17.98 Gm.
Norse group
The Norse group is a large group of retrograde irregular satellites of Saturn. Their orbital parameters are widely dispersed and the group is likely to be composed of a number of sub-groups with more homogenous orbital and physical parameters.
- Phoebe
Phoebe is thought to be a captured planetesimal from the Kuiper belt. The Phoebean surface is extremely heavily scarred, with craters up to 80 km across, one of which has walls 16 km high. Phoebe's craters show a considerable variation in brightness, which indicate the presence of large quantities of ice below a relatively thin blanket of dark surface deposits some 300 to 500 m thick. Despite its small size, Phoebe is thought to have been a hot, spherical body early in its history, with a differentiated interior, before solidifying and being battered into its current, slightly non-equilibrium shape. Material displaced from Phoebe's surface by microscopic meteor impacts may be responsible for the dark surfaces of Hyperion. Debris from the biggest impacts may have been the origin of the other moons of Phoebe's group (the Norse group) - all of which are less than 10 km in diameter.
- Size: 218.8x217x203.6 km
- Orbital period of 1.51 years at a distance of 12.96 Gm.
- Type: retrograde irregular moon
- Skathi (Skathi subgroup): 8 km size; orbital period of 1.99 years at a distance of 15.576 Gm.
- S/2007 S 2: 6 km size; orbital period of 2.17 years at a distance of 16.56 Gm.
- Skoll (Skathi subgroup): 6 km size; orbital period of 2.38 years at a distance of 17.56 Gm.
- Greip: 6 km size; orbital period of 2.48 years at a distance of 18.07 Gm.
- Hyrrokkin (Skathi subgroup): 8 km size; orbital period of 2.50 years at a distance of 18.17 Gm.
- S/2004 S 13: 6 km size; orbital period of 2.48 years at a distance of 18.06 Gm.
- S/2004 S 17: 4 km size; orbital period of 2.70 years at a distance of 19.10 Gm.
- Jarnsaxa: 6 km size; orbital period of 2.58 years at a distance of 18.56 Gm.
- Mundilfari: 7 km size; orbital period of 2.54 years at a distance of 18.36 Gm.
On 30 December 2005, when 13.1 AU from the Sun, a large chunk of Echeclus was observed to break off, causing a great cloud of dust. Astronomers have speculated this could have been caused by an impact or by an explosive release of volatile substances.
- Size: 84 km
- Orbital period of 34.96 years at a distance of 10.69 (5.82 to 15.57) AU.
- Type: Centaur
Damocloids are minor planets that have Halley-family or long-period highly eccentric orbits typical of periodic comets such as Halley's Comet, but without showing a cometary coma or tail. Their average radius is 8 km. The albedos of four damocloids have been measured, and they are among the darkest objects known in the Solar System. Damocloids are reddish in color, but not as red as many Kuiper-belt objects or centaurs.
Damocloids are believed to be nuclei of Halley-type comets that have lost all their volatile materials due to outgassing and become dormant. Such comets are believed to originate from the Oort cloud. Another strong indication of cometary origin is the fact that some damocloids have retrograde orbits, unlike any other minor planets.
Damocles's orbit reaches from inside the aphelion of Mars to as far as Uranus. It seems to be in transition from a near-circular outer Solar System orbit to an eccentric orbit taking it to the inner Solar System. There is some speculation that Damocles may have a meteor shower associated with it on Mars from the direction of Draco.
- Size: ~10 km
- Orbital period of 40.74 years at a distance of 11.84 (1.58 to 22.10) AU.
- Type: Damocloid
It is the second-known minor planet to have rings. Chiron's orbit was found to be highly eccentric, with perihelion just inside the orbit of Saturn and aphelion just outside the perihelion of Uranus. Chiron is probably a refugee from the Kuiper belt and will probably become a short-period comet in about a million years. Chiron is suspected to have two rings, similar to the better-established rings of Chariklo.
- Size: 223+/-14 km
- Orbital period of 50.76 years at a distance of 13.71 (8.51 to 18.89) AU.
- Type: Centaur
- Orbit:
Inner Ring
- 324 +/-10 km from Chiron.
- Width: ?3 km
- Depth: under investigation
Outer Ring
- ?329 +/-10 km from Chiron.
- Width: ?7 km
- Depth: under investigation
The largest confirmed centaur. It is the smallest known object to have rings. Chariklo orbits within 0.09 AU of the 4:3 mean-motion resonance with Uranus. Chariklo's rings should disperse over a period of at most a few million years, so either they are very young, or they are actively contained by shepherd moons with a mass comparable to that of the rings.
- Size: 258.6+/-10.3 km
- Orbital period of 62.59 years at a distance of 15.76 (13.05 to 18.48) AU.
- Type: Centaur
- Orbit:
Oiapoque Ring
- 396 km from Chariklo.
- Width: 3 km
- Depth: under investigation
Chui' Ring
- 405 km from Chariklo.
- Width: 7 km
- Depth: under investigation
A centaur that grazes the orbit of Uranus.
- Size: 207+/-30 km
- Orbital period of 66.85 years at a distance of 16.47 (13.17 to 19.78) AU.
- Type: Centaur
Centaurs are dark in colour, because their icy surfaces have darkened after long exposure to solar radiation and the solar wind. However, fresh craters excavate more reflective ice from below the surface. Asbolus is estimated to have an orbital half-life of about 860 kiloannum. Asbolus is currently classified as a SN centaur since Saturn is considered to control the perihelion and Neptune controls the aphelion.
- Size: 84+/-8 km
- Orbital period of 76.88 years at a distance of 18.07 (6.84 to 29.31) AU.
- Type: Centaur
Uranus is similar in composition to Neptune, and both have different bulk chemical composition from that of the larger gas giants Jupiter and Saturn. Therefore, astronomers place them in a separate category called "ice giants". Uranus has the coldest planetary atmosphere in the Solar System, with a minimum temperature of 49 K, and has a complex, layered cloud structure, with water thought to make up the lowest clouds, and methane the uppermost layer of clouds. The interior of Uranus is mainly composed of ices and rock.
Like the other giant planets, Uranus has a ring system, a magnetosphere, and numerous moons. The Uranian system has a unique configuration among those of the planets because its axis of rotation is tilted sideways, nearly into the plane of its revolution about the Sun. Its north and south poles therefore lie where most other planets have their equators. The wind speeds on Uranus can reach 250 m/s (900 kmph).
At ultraviolet and visible wavelengths, Uranus's atmosphere is bland in comparison to the other giant planets, even to Neptune, which it otherwise closely resembles. One proposed explanation for this dearth of features is that Uranus's internal heat appears markedly lower than that of the other giant planets.
- Size: 50,722+/-14 km
- Orbital period of 84.02 years at a distance of 19.20 (18.28 AU to 20.10) AU.
- Type: planet
- Orbit:
1986U2R/ζ (Zeta) Ring
A broad and faint sheet of material inward of ring 6. There is an inward gradually fading extension reaching to at least 32,600 km, or possibly even to 27,000 km - to the atmosphere of Uranus. 1986U2R is a faint, dusty ring.
- 37,000-39,500 km (1986U2R), 37,850-41,350 km (ζ) from Uranus.
- Width: 2,500 km (1986U2R), 3,500 km (ζ)
- Depth: less than 2.5 km (1986U2R), 1 km (ζ)
6 Ring
One of the dimmest of Uranus's narrow rings. It is one of the most inclined rings, and its orbital eccentricities are the largest, excluding the ε ring.
- 41,837-41,839.2 km from Uranus
- Width: 1.6-2.2 km
- Depth: around 0.41 km
5 Ring
One of the dimmest of Uranus's narrow rings. It is one of the most inclined rings, and its orbital eccentricities are the largest, excluding the ε ring.
- 42,234-42,238.9 km from Uranus
- Width: 1.9-4.9 km
- Depth: around 0.91 km
4 Ring
One of the dimmest of Uranus's narrow rings. It is one of the most inclined rings, and its orbital eccentricities are the largest, excluding the ε ring.
- 42,570-42,574.4 km from Uranus
- Width: 2.4-4.4 km
- Depth: around 0.71 km
- α (Alpha) Ring
It exhibits regular variations in brightness and width. It is brightest and widest 30° from the apoapsis and dimmest and narrowest 30° from the periapsis. The α ring has sizable orbital eccentricity and non-negligible inclination. It is geometrically thin and devoid of dust.
- 44,718-44,728 km from Uranus
- Width: 4.8-10 km
- Depth: 3.39 km
β (Beta) Ring
It exhibits regular variations in brightness and width. It is brightest and widest 30° from the apoapsis and dimmest and narrowest 30° from the periapsis. The β ring has sizable orbital eccentricity and non-negligible inclination. It is geometrically thin and devoid of dust, with a thick and optically thin dust band just outside the β ring
- 45,661-45,672.4 km from Uranus
- Width: 6.1-11.4 km
- Depth: 2.14 km
η (Eta) Ring
The η ring has zero orbital eccentricity and inclination. Like the δ ring, it consists of two components: a narrow optically dense component and a broad outward shoulder with low optical depth. The width of the narrow component is 1.9-2.7 km and the equivalent depth is about 0.42 km. The broad component is about 40 km wide and its equivalent depth is close to 0.85 km.
There is a considerable amount of dust in this ring, probably in the broad component. Like the majority of other rings, the η ring shows significant azimuthal variations in the normal optical depth and width. The narrow component even vanishes in some places.
- 47,175-47,215 km from Uranus
- Width: 1.9-40 km
- Depth: 0.42-0.85 km
γ (Gamma) Ring
A narrow, optically dense and slightly eccentric ring. Its orbital inclination is almost zero. It is geometrically thin like the ε ring and devoid of dust. The width and normal optical depth of the γ ring show significant azimuthal variations. The sharp inner edge of the γ ring is in a 6:5 resonance with Ophelia.
- 47,627-47,631.7 km from Uranus
- Width: 3.6-4.7 km
- Depth: 3.3 km
δ (Delta) Ring
The δ ring is circular and slightly inclined. It shows significant unexplained azimuthal variations in normal optical depth and width. The sharp outer edge of the δ ring is in 23:22 resonance with Cordelia. The δ ring consists of two components: a narrow optically dense component and a broad inward shoulder with low optical depth. The width of the narrow component is 4.1-6.1 km and the equivalent depth is about 2.2 km. The ring's broad component is about 10-12 km wide and its equivalent depth is close to 0.3 km. Its broad component is geometrically thicker than the narrow component.
- 48,300-48,318.1 km from Uranus
- Width: 4.1-12 km
- Depth: 0.3-2.2 km
Cordelia
Cordelia appears as an elongated object with its major axis pointing towards Uranus. Cordelia's orbit is within Uranus' synchronous orbit radius, and is therefore slowly decaying due to tidal deceleration. Cordelia is very close to a 5:3 orbital resonance with Rosalind.
- Size: 40.2+/-3 km
- Orbital period of 0.34 days at a distance of 49,752 km.
- Type: satellite
- λ (Lambda) Ring
A narrow, faint ring located just inside the ε ring, between it and the shepherd moon Cordelia. This moon clears a dark lane just inside the λ ring. The λ ring contains significant amount of micrometer-sized dust. There are azimuthal variations in the brightness of the λ ring. The variations appear to be periodic, resembling a standing wave. The origin of this fine structure in the λ ring remains a mystery.
- 50,023-50,025 km from Uranus
- Width: 1-2 km
- Depth: around 0.2 km
ε (Epsilon) Ring
The brightest and densest part of the Uranian ring system. While it is the most eccentric of the Uranian rings, it has negligible orbital inclination. The ring's eccentricity causes its brightness to vary over the course of its orbit. The radially integrated brightness of the ε ring is highest near apoapsis and lowest near periapsis. These variations are connected with the variations of the ring width, which is 19.7 km at the periapsis and 96.4 km at the apoapsis.
The geometric thickness of the ε ring is not precisely known, although the ring is certainly very thin - by some estimates as thin as 150 m. Despite such infinitesimal thickness, it consists of several layers of particles. The ring is almost devoid of dust, possibly due to the aerodynamic drag from Uranus's extended atmospheric corona. Due to its razor-thin nature the ε ring disappears when viewed edge-on. The ε ring is known to have interior and exterior shepherd moons- Cordelia and Ophelia, respectively. The inner edge of the ring is in 24:25 resonance with Cordelia, and the outer edge is in 14:13 resonance with Ophelia.
- 51,149-51,245.4 km from Uranus
- Width: 19.7-96.4 km
- Depth: around 47 km
Ophelia
Ophelia appears as an elongated object, the major axis pointing towards Uranus. Ophelia acts as the outer shepherd satellite for Uranus' Epsilon ring. The orbit of Ophelia is within the synchronous orbit radius of Uranus, and therefore the moon is slowly decaying due to tidal forces.
- Size: 42.8+/-8 km
- Orbital period of 0.38 days at a distance of 53,763 km.
- Type: satellite
Bianca
Bianca belongs to Portia Group of satellites. Bianca appears as an elongated object, the major axis pointing towards Uranus. Its surface is grey in color.
- Size: 51.4+/-4 km
- Orbital period of 0.43 days at a distance of 59,166 km.
- Type: satellite
Cressida
Cressida belongs to the Portia Group of satellites. Cressida appears as an elongated object, the major axis pointing towards Uranus. Its surface is grey in color.
- Size: 79.6+/-4 km
- Orbital period of 0.46 days at a distance of 61,767 km.
- Type: satellite
Desdemona
Desdemona belongs to Portia Group of satellites. Desdemona appears as an elongated object, the major axis pointing towards Uranus. Its surface is grey in color.
- Size: 64+/-8 km
- Orbital period of 0.47 days at a distance of 62,658 km.
- Type: satellite
Juliet
Juliet belongs to Portia Group of satellites. Juliet appears as an elongated object, the major axis pointing towards Uranus. Its surface is grey in color.
- Size: 92.6+/-8 km
- Orbital period of 0.49 days at a distance of 64,358 km.
- Type: satellite
Portia
Its orbit is slowly decaying due to tidal deceleration. Portia appears as an elongated object whose major axis points towards Uranus. It is a prolate spheroid. Its surface is grey in color.
- Size: 135.2+/-8 km
- Orbital period of 0.51 days at a distance of 66,097 km.
- Type: satellite
ν (Nu) Ring
A broad, and very faint ring. The ν ring is positioned between Portia and Rosalind and does not contain any moons inside it. The ν ring is slightly red in color.
- 66,100-69,900 km from Uranus
- Width: about 3,800 km
- Depth: around 0.012 km
Rosalind
Rosalind belongs to Portia group of satellites. It appears as an almost spherical object. Its surface is grey in color. Rosalind is very close to a 3:5 orbital resonance with Cordelia.
- Size: 72+/-12 km
- Orbital period of 0.56 days at a distance of 69,927 km.
- Type: satellite
Cupid
It has a dark surface. The orbit of Cupid differs only by 863 km from the orbit of the larger moon Belinda. Unlike Mab and Perdita, it does not seem to be perturbed.
- Size: ~18 km
- Orbital period of 0.62 days at a distance of 74,392 km.
- Type: satellite
Belinda
Belinda belongs to the Portia group of satellites. The moon is very elongated. Its surface is grey in color.
- Size: 80.6+/-1.6 km
- Orbital period of 0.62 days at a distance of 75,255 km.
- Type: satellite
Perdita
Perdita does not follow a direct Keplerian motion around Uranus. Instead, it is clearly caught in a 43:44 orbital resonance with the nearby moon Belinda. It is also close to an 8:7 resonance with Rosalind. Perdita belongs to the Portia group of satellites.
- Size: 30+/-6 km
- Orbital period of 0.64 days at a distance of 76,417+/-1 km.
- Type: satellite
Puck
Puck has a dark, heavily cratered surface, which shows spectral signs of water ice. Puck's surface is heavily cratered and is grey in color. There are three named craters on the surface of Puck, the largest being about 45 km in diameter.
Nothing is known about the internal structure of Puck. It is probably made of a mixture of water ice with the dark material similar to that found in the rings. The absence of craters with bright rays implies that Puck is not differentiated.
- Size: 162+/-4 km
- Orbital period of 0.76 days at a distance of 86,004 km.
- Type: satellite
μ (Mu) Ring
A broad, and very faint ring. The peak brightness of the μ ring lies almost exactly on the orbit of the small Uranian moon Mab. The ring is blue in color, which in turn indicates that very small (submicrometer) dust predominates within it. The dust may be made of water ice.
- 86,000-103,000 km from Uranus
- Width: about 17,000 km
- Depth: around 0.14 km
Mab
The moon is small and dark. The size of Mab is not known exactly. Mab is heavily perturbed. The actual source for perturbation is still unclear, but is presumed to be one or more of the nearby orbiting moons. Mab orbits at the same distance from Uranus as the μ (Mu) ring, a dusty ring. The moon is nearly the optimal size for dust production.
- Size: ~10 to ~48 km
- Orbital period of 0.92 days at a distance of 97,736 km.
- Type: satellite
Miranda orbits close to its planet's equatorial plane. Miranda's orbit is perpendicular to the ecliptic, and shares Uranus's extreme seasonal cycle. Miranda is one of the smallest objects in the Solar System known to be spherical under its own gravity.
Miranda has one of the most extreme and varied topographies of any object in the Solar System, including Verona Rupes, a 20-kilometer-high scarp that is the tallest cliff in the Solar System, and chevron-shaped tectonic features called coronae. The origin and evolution of this varied geology are still not fully understood.
- Size: 471.6+/-1.4 km
- Orbital period of 1.41 days at a distance of 129,390 km.
- Type: satellite
Ariel orbits and rotates in the equatorial plane of Uranus, which is almost perpendicular to the orbit of Uranus, and so has an extreme seasonal cycle. It is believed to be composed of roughly equal parts ice and rocky material. It is likely differentiated, with an inner core of rock surrounded by a mantle of ice.
Ariel has a complex surface consisting of extensive cratered terrain cross-cut by a system of scarps, canyons and ridges. The surface shows signs of more recent geological activity than other Uranian moons, most likely due to tidal heating.
- Size: 1,157.8+/-1.2 km
- Orbital period of 2.52 days at a distance of 191,020 km.
- Type: satellite
Umbriel consists mainly of ice with a substantial fraction of rock, and may be differentiated into a rocky core and an icy mantle. The surface is the darkest among Uranian moons, and appears to have been shaped primarily by impacts. However, the presence of canyons suggests early endogenic processes, and the moon may have undergone an early endogenically driven resurfacing event that obliterated its older surface.
It is covered by numerous impact craters reaching 210 km in diameter. The most prominent surface feature is a ring of bright material on the floor of Wunda crater.
- Size: 1,169.4+/-5.6 km
- Orbital period of 4.14 days at a distance of 266,000 km.
- Type: satellite
Its orbit lies inside Uranus's magnetosphere. Titania consists of approximately equal amounts of ice and rock, and is probably differentiated into a rocky core and an icy mantle. A layer of liquid water may be present at the core-mantle boundary.
The surface of Titania, which is relatively dark and slightly red in color, appears to have been shaped by both impacts and endogenic processes. It is covered with numerous impact craters reaching up to 326 km in diameter, but is less heavily cratered than the surface of Uranus's outermost moon, Oberon. Titania's surface is cut by a system of enormous canyons and scarps, the result of the expansion of its interior during the later stages of its evolution.
- Size: 1,576.8+/-1.2 km
- Orbital period of 8.71 days at a distance of 435,910 km.
- Type: satellite
It is likely that Oberon formed from the accretion disk that surrounded Uranus just after the planet's formation. The moon consists of approximately equal amounts of ice and rock, and is probably differentiated into a rocky core and an icy mantle. A layer of liquid water may be present at the boundary between the mantle and the core.
The surface of Oberon, which is dark and slightly red in color, appears to have been primarily shaped by asteroid and comet impacts. It is covered by numerous impact craters reaching 210 km in diameter. Oberon possesses a system of chasmata (graben or scarps) formed during crustal extension as a result of the expansion of its interior during its early evolution.
- Size: 1,522.8+/-5.2 km
- Orbital period of 13.46 days at a distance of 583,520 km.
- Type: satellite
Magnetosphere Bow Shock
Uranus's magnetic field is peculiar, both because it does not originate from its geometric centre, and because it is tilted at 59° from the axis of rotation. In fact the magnetic dipole is shifted from the Uranus's center towards the south rotational pole by as much as one third of the planetary radius. This unusual geometry results in a highly asymmetric magnetosphere. Neptune has a similarly displaced and tilted magnetic field, suggesting that this may be a common feature of ice giants. One hypothesis is that, unlike the magnetic fields of the terrestrial and gas giants, which are generated within their cores, the ice giants' magnetic fields are generated by motion at relatively shallow depths, for instance, in the water-ammonia ocean.
Overall, the structure of Uranus's magnetosphere is different from Jupiter's and more similar to Saturn's. Uranus's magnetotail trails behind it into space for millions of kilometres and is twisted by its sideways rotation into a long corkscrew. The particle population is strongly affected by the Uranian moons, which sweep through the magnetosphere, leaving noticeable gaps. The particle flux is high enough to cause darkening or space weathering of their surfaces on an astronomically rapid timescale of 100,000 years. This may be the cause of the uniformly dark colouration of the Uranian satellites and rings. Uranus has relatively well developed aurorae, which are seen as bright arcs around both magnetic poles.
- Bow shock: 587,857 km from Uranus
Francisco
- Size: est. 22 km
- Orbital period of -266.56 days at a distance of 4.28 Gm.
- Type: retrograde irregular satellite
Caliban
Its orbit is retrograde, moderately inclined and slightly eccentric. Caliban is hypothesized to be a captured object.
- Size: est. 72 km
- Orbital period of -1.59 years at a distance of 7.23 Gm.
- Type: retrograde irregular satellite
Stephano
The orbital parameters suggest that it may belong to the same dynamic cluster as Caliban, suggesting a common origin.
- Size: est. 32 km
- Orbital period of -1.85 years at a distance of 8.00 Gm.
- Type: retrograde irregular satellite
Trinculo
- Size: est. 18 km
- Orbital period of -2.51 years at a distance of 8.50 Gm.
- Type: retrograde irregular satellite
Sycorax
Its orbit is retrograde, moderately inclined and eccentric. Sycorax is hypothesized to be a captured object. It appears light-red in the visible spectrum, redder than Himalia but still less red than most Kuiper belt objects. The rotation period of Sycorax is estimated at about 3.6 hours.
- Size: est. 150 km
- Orbital period of -3.53 years at a distance of 12.18 Gm.
- Type: retrograde irregular satellite
Margaret
It's inclination of 57° is close to the limit of stability.
- Size: est. 20 km
- Orbital period of -4.62 years at a distance of 14.35 Gm.
- Type: prograde irregular satellite
Prospero
It appears neutral (grey) in visible light.
- Size: est. 50 km
- Orbital period of -5.42 years at a distance of 16.26 Gm.
- Type: retrograde irregular satellite
Setebos
It appears neutral (grey) in visible light.
- Size: est. 48 km
- Orbital period of -6.09 years at a distance of 17.42 Gm.
- Type: retrograde irregular satellite
Ferdinand
It follows a retrograde, modestly inclined but highly eccentric orbit.
- Size: est. 12 km
- Orbital period of -7.90 years at a distance of 20.9 Gm.
- Type: retrograde irregular satellite
In an eccentric orbit, with a perihelion less than Saturn's and aphelion greater than Neptune's. It is believed that Pholus originated in the Kuiper belt. It is quite red in color, for which it has been occasionally nicknamed "Big Red". It has shown no signs of cometary activity.
- Size: 185+/-16 km
- Orbital period of 91.85 years at a distance of 20.36 (8.73 to 31.98) AU.
- Type: Centaur
Notable for its unusual orbit, which is highly eccentric and retrograde. It is one of twenty or so known minor planets in the Solar System that have a retrograde orbit. Dioretsa's orbit is otherwise similar to that of a comet. This has led to speculation that Dioretsa was originally an object from the Oort cloud.
- Size: 14+/-3 km
- Orbital period of 115.94 years at a distance of 23.78 (2.39 to 45.16) AU.
- Type: Centaur, Damocloid
Nessus is an "SE object" because currently Saturn controls its perihelion and its aphelion is within the Kuiper belt.
- Size: 60+/-16 km
- Orbital period of 122.42 years at a distance of 24.66 (11.83 to 37.48) AU.
- Type: Centaur
Currently Uranus controls Hylonome's perihelion and Neptune its aphelion.
- Size: 70+/-20 km
- Orbital period of 126 years at a distance of 25.13 (18.92 to 31.35) AU.
- Type: Centaur
Amycus lies within 0.009 AU of the 3:4 resonance of Uranus.
- Size: 76.3+/-12.5 km
- Orbital period of 126.12 years at a distance of 25.15 (15.21 to 35.09) AU.
- Type: Centaur
Neptune is the farthest planet from the Sun in the Solar System, and is the fourth-largest planet by diameter and the third-largest by mass. Among the gaseous planets in the Solar System, Neptune is the most dense. Neptune is slightly more massive than its near-twin Uranus. Neptune is similar in composition to Uranus. Astronomers sometimes categorise Uranus and Neptune as "ice giants" to emphasise this distinction from Jupiter and Saturn. The interior of Neptune is primarily composed of ices and rock.
Neptune's atmosphere has active and visible weather patterns. These weather patterns are driven by the strongest sustained winds of any planet in the Solar System, with recorded wind speeds as high as 2,100 kmph. Because of its great distance from the Sun, Neptune's outer atmosphere is one of the coldest places in the Solar System, with temperatures at its cloud tops approaching 55 K.
Neptune's weather is characterised by extremely dynamic storm systems. Most of the winds on Neptune move in a direction opposite the planet's rotation. The general pattern of winds showed prograde rotation at high latitudes vs. retrograde rotation at lower latitudes. Because of seasonal changes, the cloud bands in the southern hemisphere of Neptune have been observed to increase in size and albedo. The long orbital period of Neptune results in seasons lasting forty years.
- Size: 49,244+/-38 km
- Orbital period of 164.8 years at a distance of 30.07 (29.81 to 30.33) AU.
- Type: planet
- Orbit:
- Grande Savoie Residential Area
- Kim Saintlaurent born here on 2023.10.03.
Galle Ring
A faint ring.
- Orbital radius: 41,000 - 43,000 km
- Width: about 2,000 km
- Depth: around 0.15 km
Naiad
It is irregularly shaped and probably has not been modified by any internal geological processes since its formation. It is likely that it is a rubble pile. Naiad orbits below the synchronous orbit radius, and its orbit is slowly decaying due to tidal deceleration. Naiad orbits Neptune well within its fluid Roche limit, and its density is expected to be low enough that it may be very close to its actual Roche limit already.
- Size: 96x60x52 km
- Orbital period of 0.29 days at a distance of 48,227+/-1 km.
- Type: satellite
Thalassa
It is irregularly shaped and shows no sign of any geological modification. It is likely that it is a rubble pile. Unusually for irregular bodies, it appears to be roughly disk-shaped. Since the Thalassian orbit is below Neptune's synchronous orbit radius, it is slowly spiralling inward due to tidal deceleration.
- Size: 108x100x52 km
- Orbital period of 0.31 days at a distance of 50,075+/-1 km.
- Type: satellite
Despina
It is irregularly shaped and shows no sign of any geological modification. It is likely that it is a rubble pile. Despina's orbit lies close to but outside of the orbit of Thalassa and just inside the Le Verrier ring. As it is also below Neptune's synchronous orbit radius, it is slowly spiralling inward due to tidal deceleration.
- Size: 180x148x128 km
- Orbital period of 0.33 days at a distance of 52,526+/-1 km.
- Type: satellite
- Le Verrier Ring
A narrow ring. The small moon Despina may play a role in the ring's confinement by acting as a shepherd.
- Orbital radius: 53,200 km
- Width: about 113 km
- Depth: around 0.7+/-0.2 km
Lassell Ring
Also known as the plateau, is the broadest ring in the Neptunian system. This ring is a faint sheet of material occupying the space between the Le Verrier ring and the Arago ring.
- Orbital radius: 53,200 km to 57,200 km
- Width: about 4,000 km
- Depth: around 0.4 km
Arago Ring
There is a small peak of brightness near the outer edge of the Lassell ring, that some planetary scientists call the Arago ring.
- Orbital radius: 57,200 km
- Width: less than 100 km
- Depth: under investigation
Galatea
It is irregularly shaped and shows no sign of any geological modification. It is likely that it is a rubble pile. Galatea's orbit lies below Neptune's synchronous orbit radius, so it is slowly spiralling inward due to tidal deceleration.
- Size: 204x184x144 km
- Orbital period of 0.43 days at a distance of 61,953+/-1 km.
- Type: satellite
Adams Ring
This ring is narrow, slightly eccentric and inclined. Neptune's small moon Galatea acts like a shepherd, keeping ring particles inside a narrow range of orbital radii through a 42:43 outer Lindblad resonance. Galatea's gravitational influence creates 42 radial wiggles in the Adams ring with an amplitude of about 30 km.
The ring arcs, the brightest parts of the Adams ring, are discrete regions within the ring in which the particles that it comprises are mysteriously clustered together. There are five short arcs, which occupy a relatively narrow range of longitudes from 247° to 294°: Fraternité - the brightest and longest arc, Égalité 1, Égalité 2, Liberté, and Courage - the faintest arc. The arcs are quite stable structures.
- Orbital radius: about 63,930 km
- Width: 15-50 km
- Depth: around 0.011+/-0.003 outside the arcs, which are about 0.4 km.
Larissa
Larissa is irregular (non-spherical) in shape and appears to be heavily cratered, with no sign of any geological modification. It is likely that Larissa is a rubble pile. Larissa's orbit is circular but not perfect and lies below Neptune's synchronous orbit radius, so it is slowly spiralling inward due to tidal deceleration.
- Size: 216x204x168+/-10 km
- Orbital period of 0.55 days at a distance of 73,548 km.
- Type: satellite
Proteus circles Neptune in a nearly equatorial orbit at the distance of about 4.75 equatorial radii of the planet. It has a somewhat irregular shape with several slightly concave facets and relief as high as 20 km. Its surface is dark, neutral in color and heavily cratered. The largest crater is more than 200 km in diameter. There are also a number of scarps, grooves and valleys related to large craters. Proteus is probably not an original body that formed with Neptune; it may have accreted later from the debris created when the largest Neptunian satellite Triton was captured.
- Size: 424x390x396 km
- Orbital period of 1.12 days at a distance of 117,647 km (117,584 to 117,709 km).
- Type: satellite
Because of its retrograde orbit and composition similar to Pluto's, Triton is thought to have been captured from the Kuiper belt. Triton has a surface of mostly frozen nitrogen, a mostly water ice crust, an icy mantle and a substantial core of rock and metal. The core makes up two-thirds of its total mass.
Triton is one of the few moons in the Solar System known to be geologically active. As a consequence, its surface is relatively young, with a complex geological history revealed in intricate cryovolcanic and tectonic terrains. Part of its crust is dotted with geysers thought to erupt nitrogen. Triton has a tenuous nitrogen atmosphere.
Triton is in synchronous rotation with Neptune; it keeps one face oriented toward the planet at all times. Its equator is almost exactly aligned with its orbital plane. At present, at some point during Neptune's year each pole points fairly close to the Sun. As Neptune orbits the Sun, Triton's polar regions take turns facing the Sun, resulting in seasonal changes as one pole, then the other, moves into the sunlight.
- Size: 2,706.8+/-1.8 km
- Orbital period of -5.88 days at a distance of 354,759 km.
- Type: satellite
Magnetosphere Bow Shock
Neptune also resembles Uranus in its magnetosphere, with a magnetic field strongly tilted relative to its rotational axis at 47° and offset at least about 13,500 km from the planet's physical centre. Neptune's bow shock, where the magnetosphere begins to slow the solar wind, occurs at a distance of 34.9 times the radius of the planet. The magnetopause, where the pressure of the magnetosphere counterbalances the solar wind, lies at a distance of 23-26.5 times the radius of Neptune. The tail of the magnetosphere extends out to at least 72 times the radius of Neptune, and likely much farther.
- Bow shock: 864,263 km from Neptune
It has a highly eccentric orbit. The unusual orbit suggests that it may be either a captured asteroid or Kuiper belt object, or that it was an inner moon in the past and was perturbed during the capture of Neptune's largest moon Triton. Nereid appears neutral in colour and water ice has been detected on its surface.
- Size: 170+/-25 km
- Orbital period of 360.14 days at a distance of 5.51 Gm (1.37 to 9.66 Gm).
- Type: irregular Satellite
Halimede
It appears neutral (grey) in the visible light. Given the very similar colour of the satellite to that of Nereid together with the high probability (41%) of collision in the past lifespan of the Solar System, it has been suggested that the satellite could be a fragment of Nereid.
- Size: 62 km
- Orbital period of -5.14 years at a distance of 16.61 Gm.
- Type: irregular satellite
Sao
Sao follows an exceptionally inclined and moderately eccentric orbit in relation to other irregular satellites of Neptune.
- Size: 44 km
- Orbital period of 7.97 years at a distance of 22.23 Gm.
- Type: irregular satellite
Laomedeia
A prograde irregular satellite of Neptune.
- Size: 42 km
- Orbital period of 8.68 years at a distance of 23.57 Gm.
- Type: irregular satellite
Psamathe
The orbit of this satellite is close to the theoretical stable separation from Neptune for a body in a retrograde orbit. Given the similarity of Psamathe's orbital parameters with Neso, it was suggested that both irregular satellites could have a common origin in the break-up of a larger moon.
- Size: 38 km
- Orbital period of -24.84 years at a distance of 48.10 Gm.
- Type: irregular satellite
Neso
It follows a highly inclined and highly eccentric orbit in relation to other irregular satellites of Neptune. Given the similarity of the orbit's parameters with Psamathe, it was suggested that both irregular satellites could have a common origin in the break-up of a larger moon.
- Size: 60 km
- Orbital period of -26.67 years at a distance of 49.29 Gm (0.33 AU).
- Type: irregular satellite
Neptune trojans are bodies in orbit around the Sun that orbit near one of the stable Lagrangian points of Neptune. They therefore have approximately the same orbital period as Neptune and follow roughly the same orbital path. The discovery of 2005 TN
53 in a high-inclination (>25°) orbit was significant, because it suggested a "thick" cloud of trojans, which is indicative of freeze-in capture instead of in situ or collisional formation. It is suspected that large (radius ≈ 100 km) Neptune trojans could outnumber Jupiter trojans by an order of magnitude.
The orbits of Neptune trojans are highly stable; Neptune may have retained up to 50% of the original post-migration trojan population over the age of the Solar System. The original population of trojans probably contained many objects on dynamically unstable orbits, and the current trojan population continues to contribute centaurs. On the other hand, a trojan on a stable orbit need not be primordial.
The first four discovered Neptune trojans have similar colors. They are modestly red, slightly redder than the gray Kuiper belt objects, but not as extremely red as the high-perihelion cold classical Kuiper belt objects. This is similar to the colors of the blue lobe of the centaur color distribution, the Jupiter trojans, the irregular satellites of the gas giants, and possibly the comets, which is consistent with a similar origin of these populations of small Solar System bodies.
- Neptune Trojans - L4 Group
Orbits the L4 Lagrangian point of the Sun-Neptune system, about 60° ahead Neptune.
- 2006 RJ103: 85-190 km size; orbital period of 165.9 years at a distance of 30.20 (29.31 to 31.08) AU.
- 2007 VL305: 65-150 km size; orbital period of 166 years at a distance of 30.20 (28.13 to 32.27) AU.
- 2005 TN53: 40-90 km size; orbital period of 166.6 years at a distance of 30.28 (28.20 to 32.36) AU.
- 2005 TO74: ~100 km size; orbital period of 166.6 years at a distance of 30.28 (28.67 to 31.89) AU.
- 2004 UP10: ?? km size; orbital period of 166.93 years at a distance of 30.32 (29.34 to 31.29) AU.
- 2001 QR322: 60-160 km size; orbital period of 167.59 years at a distance of 30.40 (29.47 to 31.33) AU.
- Neptune Trojans - L5 Group
Orbits the L5 Lagrangian point of the Sun-Neptune system, about 60° behind Neptune.
- 2008 LC18: ~100 km size; orbital period of 163.6 years at a distance of 29.91 (27.4 to 32.5) AU.
- 2011 HM102: 90-180 km size; orbital period of 164.73 years at a distance of 30.05 (27.69 to 32.41) AU.
- 2004 KV18: ~56 km size; orbital period of 165.35 years at a distance of 30.12 (24.54 to 35.70) AU.
A temporary quasi-satellite of Neptune. Prior to the quasi-satellite dynamical state, 2007 RW
10 was an L
5 trojan, and it will go back to that state soon after leaving its current quasi-satellite orbit. Its orbital inclination is the largest among known Neptune co-orbitals. It is also possibly the largest known object trapped in the 1:1 mean-motion resonance with any major planet.
- Size: 247+/-30 km
- Orbital period of 166.98 years at a distance of 30.32 (21.24 to 39.41) AU.
- Type: TNO
A TNO in a Centaur-like orbit.
- Size: 192 km
- Orbital period of 184.49 years at a distance of 32.41 (17.64 to 47.17) AU.
- Type: TNO, Centaur
REFERENCES
© Aaron Sketchley
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