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Planet Nine is a hypothetical ninth planet in the outer region of the Solar System. [2] [4] 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 (AUs).
An asteroid is a minor planet —an object that is neither a true planet nor an identified comet — that orbits within the inner Solar System. They are rocky, metallic, or icy bodies with no atmosphere, classified as C-type (carbonaceous), M-type (metallic), or S-type (silicaceous).
Below are the descriptions of the three largest bodies in the asteroid belt. They are all considered to be relatively intact protoplanets, a precursor stage before becoming a fully-formed planet (see List of exceptional asteroids): [143] [144] [145] Ceres (2.55–2.98 AU) is the only dwarf planet in the asteroid belt. [146]
Lists of astronomical objects. Selection of astronomical bodies and objects: Moon Mimas and Ida, an asteroid with its own moon, Dactyl. Comet Lovejoy and Jupiter, a giant gas planet. The Sun; Sirius A with Sirius B, a white dwarf; the Crab Nebula, a remnant supernova. A black hole (artist concept); Vela Pulsar, a rotating neutron star.
Astronomical naming conventions. In ancient times, only the Sun and Moon, a few stars, and the most easily visible planets had names. Over the last few hundred years, the number of identified astronomical objects has risen from hundreds to over a billion, and more are discovered every year. Astronomers need to be able to assign systematic ...
The following is a list of Solar System objects by orbit, ordered by increasing distance from the Sun. Most named objects in this list have a diameter of 500 km or more. The Sun, a spectral class G2V main-sequence star. The inner Solar System and the terrestrial planets. Mercury. Mercury-crossing minor planets. Venus. Venus-crossing minor planets.
The Oort cloud (/ ɔːrt, ʊərt /), [1] sometimes called the Öpik–Oort cloud, [2] is theorized to be a vast cloud of icy planetesimals surrounding the Sun at distances ranging from 2,000 to 200,000 AU (0.03 to 3.2 light-years). [3][note 1][4] The concept of such a cloud was proposed in 1950 by the Dutch astronomer Jan Oort, in whose honor ...
Examples of astronomical objects include planetary systems, star clusters, nebulae, and galaxies, while asteroids, moons, planets, and stars are astronomical bodies. A comet may be identified as both a body and an object: It is a body when referring to the frozen nucleus of ice and dust, and an object when describing the entire comet with its ...