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These moons all orbit beyond the E Ring. They are: Rhea is the second-largest of Saturn's moons. It is even slightly larger than Oberon, the second-largest moon of Uranus. [53] In 2005, Cassini detected a depletion of electrons in the plasma wake of Rhea, which forms when the co-rotating plasma of Saturn's magnetosphere is absorbed by the moon ...
The known icy moons in this range are all ellipsoidal (except Proteus), but trans-Neptunian objects up to 450–500 km radius may be quite porous. [10] For simplicity and comparative purposes, the values are manually calculated assuming that the bodies are all spheres. The size of solid bodies does not include an object's atmosphere.
Asteroid moons; A number of smaller groups distinct from the asteroid belt; The outer Solar System with the giant planets, their satellites, trojan asteroids and some minor planets. Jupiter. Rings of Jupiter; Complete list of Jupiter's natural satellites. Galilean moons. Io; Europa; Ganymede; Callisto; Jupiter trojans; Jupiter-crossing minor ...
Nineteen moons are large enough to be round, and two, Titan and Triton, have substantial atmospheres The number of moons discovered in each year until November 2019 Mercury , the smallest and innermost planet, has no moons, or at least none that can be detected to a diameter of 1.6 km (1.0 mi). [ 2 ]
The rings would initially have been much more massive (≈1,000 times) and broader than at present; material in the outer portions of the rings would have coalesced into the innermost moons of Saturn (those closest to Saturn), out to Tethys, also explaining the lack of rocky material in the composition of most of these moons. [65]
Fainter planetary rings can form as a result of meteoroid impacts with moons orbiting around the planet or, in the case of Saturn's E-ring, the ejecta of cryovolcanic material. [ 6 ] [ 7 ] Ring systems may form around centaurs when they are tidally disrupted in a close encounter (within 0.4 to 0.8 times the Roche limit ) with a giant planet.
The moons of the trans-Neptunian objects (other than Charon) have not been included, because they appear to follow the normal situation for TNOs rather than the moons of Saturn and Uranus, and become solid at a larger size (900–1000 km diameter, rather than 400 km as for the moons of Saturn and Uranus).
Regular moons may also originate from secondary disruption events, being fragments of other regular moons following collisions or due to tidal disruption. The regular moons of Neptune are likely examples of this, as the capture of Neptune's largest moon—Triton—would have severely disrupted the existing primordial moon system. Once Triton ...