Oort cloud. An artist's rendering of the Oort cloud and the Kuiper belt (inset).
Sizes of individual objects have been exaggerated for visibility. The Oort cloud /ˈɔrt/[1] (named after the Dutch astronomer Jan Oort), or Öpik–Oort cloud,[2] is a hypothesized spherical cloud of predominantly icy planetesimals that may lie roughly 50,000 AU, or nearly a light-year, from the Sun.[3] This places the cloud at nearly a quarter of the distance to Proxima Centauri, the nearest star to the Sun. The Kuiper belt and the scattered disc, the other two reservoirs of trans-Neptunian objects, are less than one thousandth of the Oort cloud's distance. The outer limit of the Oort cloud defines the cosmographical boundary of the Solar System and the region of the Sun's gravitational dominance.[4] The Oort cloud is thought to comprise two separate regions: a spherical outer Oort cloud and a disc-shaped inner Oort cloud, or Hills cloud.
Hypothesis[edit] Structure and composition[edit] Origin[edit] In June 2010 Harold F. Scattered disc. Although the closest scattered-disc objects approach the Sun at about 30–35 AU, their orbits can extend well beyond 100 AU.
This makes scattered objects among the most distant and coldest objects in the Solar System.[1] The innermost portion of the scattered disc overlaps with a torus-shaped region of orbiting objects traditionally called the Kuiper belt,[2] but its outer limits reach much farther away from the Sun and farther above and below the ecliptic than the Kuiper belt proper. [a] Discovery[edit] Traditionally, devices like a blink comparator were used in astronomy to detect objects in the Solar System, because these objects would move between two exposures—this involved time-consuming steps like exposing and developing photographic plates or films, and people then using a blink comparator to manually detect prospective objects.
Subdivisions of trans-Neptunian space[edit] Scattered disc versus Kuiper belt[edit] Detached objects[edit] An alternative classification, introduced by B. Kuiper belt. The Kuiper belt is distinct from the theoretical Oort cloud, which is a thousand times more distant and is mostly spherical.
The objects within the Kuiper belt, together with the members of the scattered disc and any potential Hills cloud or Oort cloud objects, are collectively referred to as trans-Neptunian objects (TNOs).[12] Pluto is the largest and most massive member of the Kuiper belt, and the largest and the second-most-massive known TNO, surpassed only by Eris in the scattered disc. [nb 1] Originally considered a planet, Pluto's status as part of the Kuiper belt caused it to be reclassified as a dwarf planet in 2006. It is compositionally similar to many other objects of the Kuiper belt and its orbital period is characteristic of a class of KBOs, known as "plutinos", that share the same 2:3 resonance with Neptune. History[edit] After the discovery of Pluto in 1930, many speculated that it might not be alone.
Hypotheses[edit] Discovery[edit] Name[edit] Asteroid belt "doughnut shaped" Solar System Exploration: Planet Selector: Asteroids. Asteroids. Kuiper Belt & Oort Cloud.