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The listed objects currently include most objects in the asteroid belt and moons of the giant planets in this size range, but many newly discovered objects in the outer Solar System are missing, such as those included in the following reference. [58] Asteroid spectral types are mostly Tholen, but some might be SMASS.
Of the Solar System's eight planets and its nine most likely dwarf planets, six planets and seven dwarf planets are known to be orbited by at least 300 natural satellites, or moons. At least 19 of them are large enough to be gravitationally rounded; of these, all are covered by a crust of ice except for Earth's Moon and Jupiter's Io. [1]
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."
There are 146 moons with confirmed orbits, the most of any planet in the Solar System. [1] [a] This number does not include the many thousands of moonlets embedded within Saturn's dense rings, nor hundreds of possible kilometer-sized distant moons that have been observed on single occasions.
A planet usually has at least around 10,000 times the mass of any natural satellites that orbit it, with a correspondingly much larger diameter. [3] The Earth–Moon system is a unique exception in the Solar System; at 3,474 kilometres (2,158 miles) across, the Moon is 0.273 times the diameter of Earth and about 1 ⁄ 80 of its mass. [4]
Oldest, largest and most massive planet in the Solar System; [239] this planet hosts 95 known moons including the Galilean moons. Reported for reference. For smaller exoplanets, see the list of smallest exoplanets or other lists of exoplanets. For exoplanets with milestones, see the list of exoplanet extremes and list of exoplanet firsts.
It is slightly more massive than the second most massive moon, Saturn's satellite Titan, and is more than twice as massive as the Earth's Moon. It is larger than the planet Mercury, which has a diameter of 4,880 kilometres (3,030 mi) but is only 45 percent of Mercury's mass. Ganymede is the ninth-largest object in the solar system, but the ...
Neptune has the largest Hill sphere in the Solar System, owing primarily to its large distance from the Sun; this allows it to retain control of such distant moons. [19] Nevertheless, the Jovian moons in the Carme and Pasiphae groups orbit at a greater percentage of their primary's Hill radius than the Neso group moons.