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The eight planets of the Solar System with size to scale (up to down, left to right): Saturn, Jupiter, Uranus, Neptune (outer planets), Earth, Venus, Mars, and Mercury (inner planets) A planet is a large, rounded astronomical body that is generally required to be in orbit around a star, stellar remnant, or brown dwarf, and is not one itself. [1]
The best available theory of planet formation is the nebular hypothesis, which posits that an interstellar cloud collapses out of a nebula to create a young protostar orbited by a protoplanetary disk. There are eight planets within the Solar System; planets outside of the solar system are also known as exoplanets.
By 1989, all eight planets have been visited by space probes. [297] Probes have returned samples from comets [298] and asteroids, [299] as well as flown through the Sun's corona [300] and visited two dwarf planets (Pluto and Ceres).
A planet in the Solar System beyond the asteroid belt, and hence refers to the gas giants. Pulsar planet: A planet that orbits a pulsar or a rapidly rotating neutron star. Rogue planet: Also known as an interstellar planet. A planetary-mass object that orbits the galaxy directly. Superior planets: Planets whose orbits lie outside the orbit of ...
For the giant planets, the "radius" is defined as the distance from the center at which the atmosphere reaches 1 bar of atmospheric pressure. [ 11 ] Because Sedna and 2002 MS 4 have no known moons, directly determining their mass is impossible without sending a probe (estimated to be from 1.7x10 21 to 6.1×10 21 kg for Sedna [ 12 ] ).
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; M80, a globular cluster, and the Pleiades, an open star cluster; The Whirlpool galaxy and Abell 2744, a galaxy cluster; Superclusters, galactic ...
All exoplanets orbit around star A in the binary system. 47 Ursae Majoris: Ursa Major: 10 h 59 m 27.97 s +40° 25′ 48.9″ 5.10: 46: G0V: 1.029: 5892: 7.434: 3: Planet Taphao Thong was discovered in 1996 and was one of the first exoplanets to be discovered. [48] The planet was the first long-period extrasolar planet discovered. The other ...
This is a list of space probes that have left Earth orbit (or were launched with that intention but failed), organized by their planned destination. It includes planetary probes, solar probes, and probes to asteroids and comets, but excludes lunar missions, which are listed separately at List of lunar probes and List of Apollo missions.