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The orbits of Solar System planets are nearly circular. Compared to many other systems, they have smaller orbital eccentricity. [69] Although there are attempts to explain it partly with a bias in the radial-velocity detection method and partly with long interactions of a quite high number of planets, the exact causes remain undetermined. [69] [73]
There is evidence that the formation of the Solar System began about 4.6 billion years ago with the gravitational collapse of a small part of a giant molecular cloud. [ 1 ] Most of the collapsing mass collected in the center, forming the Sun, while the rest flattened into a protoplanetary disk out of which the planets, moons, asteroids, and ...
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]
Neptune is the eighth and farthest known planet from the Sun. It is the fourth-largest planet in the Solar System by diameter, the third-most-massive planet, and the densest giant planet. It is 17 times the mass of Earth and slightly more massive, but denser and smaller, than fellow ice giant Uranus.
Jupiter is the fifth planet from the Sun and the largest in the Solar System.It is a gas giant with a mass more than 2.5 times that of all the other planets in the Solar System combined and slightly less than one-thousandth the mass of the Sun. Jupiter orbits the Sun at a distance of 5.20 AU (778.5 Gm), with an orbital period of 11.86 years.
Saturn is the sixth planet from the Sun and the second largest in the Solar System, after Jupiter. It is a gas giant , with an average radius of about nine and a half times that of Earth . [ 26 ] [ 27 ] It has an eighth the average density of Earth, but is over 95 times more massive.
Alpha Centauri ( α Centauri, α Cen, or Alpha Cen) is a triple star system in the southern constellation of Centaurus. It consists of three stars: Rigil Kentaurus ( α Centauri A ), Toliman ( α Centauri B ), and Proxima Centauri ( α Centauri C ). [14] Proxima Centauri is the closest star to the Sun at 4.2465 light-years (1.3020 pc ).
Mercury is one of four terrestrial planets in the Solar System, which means it is a rocky body like Earth. It is the smallest planet in the Solar System, with an equatorial radius of 2,439.7 kilometres (1,516.0 mi). [4] Mercury is also smaller—albeit more massive—than the largest natural satellites in the Solar System, Ganymede and Titan.