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Charon has an angular diameter of 4 degrees of arc as seen from the surface of Pluto; the Sun appears much smaller, only 39 to 65 arcseconds. By comparison, the Moon as viewed from Earth has an angular diameter of only 31 minutes of arc, or just over half a degree of arc. Therefore, Charon would appear to have eight times the diameter, or 25 ...
The sizes and masses of many of the moons of Jupiter and Saturn are fairly well known due to numerous observations and interactions of the Galileo and Cassini orbiters; however, many of the moons with a radius less than ~100 km, such as Jupiter's Himalia, have far less certain masses. [5]
The timeline of discovery of Solar System planets and their natural satellites charts the progress of the discovery of new bodies over history. Each object is listed in chronological order of its discovery (multiple dates occur when the moments of imaging, observation, and publication differ), identified through its various designations (including temporary and permanent schemes), and the ...
Among the other dwarf planets, Ceres has no known moons. It is 90 percent certain that Ceres has no moons larger than 1 km in size, assuming that they would have the same albedo as Ceres itself. [6] Eris has one large known moon, Dysnomia. Accurately determining its size is difficult: one indicative estimate of its radius is 350 ± 57.5 km. [7]
Chiron, a moon of Saturn supposedly sighted by Hermann Goldschmidt in 1861 but never observed by anyone else.; Chrysalis, a hypothetical moon of Saturn, named in 2022 by scientists of the Massachusetts Institute of Technology using data from the Cassini–Huygens mission, thought to have been torn apart by Saturn's tidal forces, somewhere between 200 and 100 million years ago, with up to 99% ...
The distinction between a satellite and a classical planet was not recognized until after the heliocentric model of the Solar System was established. When in 1610 Galileo discovered the first satellites of another planet (the four Galilean moons of Jupiter), he referred to them as "four planets flying around the star of Jupiter at unequal intervals and periods with wonderful swiftness."
Mars has two relatively small (compared to Earth's) natural moons, Phobos (about 22 kilometres (14 mi) in diameter) and Deimos (about 12 kilometres (7.5 mi) in diameter), which orbit close to the planet. The origin of both moons is unclear, although a popular theory states that they were asteroids captured into Martian orbit. [199]
The study of the outer planets has since been revolutionized by the use of uncrewed space probes. The arrival of the Voyager spacecraft at Saturn in 1980–1981 resulted in the discovery of three additional moons—Atlas, Prometheus and Pandora—bringing the total to 17. [21] In addition, Epimetheus was confirmed as distinct from Janus.