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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 ...
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]
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 ...
Planet Nine is a hypothetical ninth planet in the outer region of the Solar System. [4] [2] Its gravitational effects could explain the peculiar clustering of orbits for a group of extreme trans-Neptunian objects (ETNOs), bodies beyond Neptune that orbit the Sun at distances averaging more than 250 times that of the Earth i.e. over 250 astronomical units (AU).
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 ...
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.
Additional planets in the outer reaches of the Solar System, such as a ninth planet beyond Neptune or especially a tenth beyond Pluto (between the 1930 discovery of Pluto and its reclassification from planet to dwarf planet in 2006), appear regularly. Many different names for this hypothetical outermost planet have been used, the most common ...