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The search began in the mid-19th century and continued at the start of the 20th with Percival Lowell's quest for Planet X. Lowell proposed the Planet X hypothesis to explain apparent discrepancies in the orbits of the giant planets, particularly Uranus and Neptune, [2] speculating that the gravity of a large unseen ninth planet could have ...
This is a list of trans-Neptunian objects (TNOs), which are minor planets in the Solar System that orbit the Sun at a greater distance on average than Neptune, that is, their orbit has a semi-major axis greater than 30.1 astronomical units (AU). The Kuiper belt, scattered disk, and Oort cloud are three conventional divisions of this volume of ...
Pluto (minor-planet designation: 134340 Pluto) is a dwarf planet in the Kuiper belt, a ring of bodies beyond the orbit of Neptune. It is the ninth-largest and tenth-most-massive known object to directly orbit the Sun. It is the largest known trans-Neptunian object by volume by a small margin, but is less massive than Eris.
The astronomer Julio Angel Fernandez published a paper in 1980 suggesting the existence of a comet belt beyond Neptune [12] [13] which could serve as a source for short-period comets. [14] [15] In 1992, minor planet (15760) Albion was discovered, the first Kuiper belt object (KBO) since Pluto (in 1930) and Charon (in 1978). [16]
Planets whose orbits lie within the orbit of Earth. [nb 1] Mercury and Venus: Inner planet: A planet in the Solar System that have orbits smaller than the asteroid belt. [nb 2] Mercury, Venus, Earth, Mars: Outer planet: A planet in the Solar System beyond the asteroid belt, and hence refers to the gas giants. Jupiter, Saturn, Uranus and Neptune ...
A large number of trans-Neptunian objects (TNOs) – minor planets orbiting beyond the orbit of Neptune – have been discovered in recent years. Many TNOs have orbits that take them far beyond Pluto's aphelion of 49.3 AU.
Astronomers have discovered a new moon orbiting Uranus — the first spotted in nearly 20 years — and two new moons around Neptune.
Planet V, a planet thought by John Chambers and Jack Lissauer to have once existed between Mars and the asteroid belt, based on computer simulations. Various planets beyond Neptune: Planet Nine, a planet proposed to explain apparent alignments in the orbits of a number of distant trans-Neptunian objects. Planet X, a hypothetical planet beyond ...