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The Oort cloud is thought to have developed after the formation of planets from the primordial protoplanetary disc approximately 4.6 billion years ago. [4] The most widely accepted hypothesis is that the Oort cloud's objects initially coalesced much closer to the Sun as part of the same process that formed the planets and minor planets.
The concept of such a cloud was proposed in 1950 by the Dutch astronomer Jan Oort, in whose honor the idea was named. Oort proposed that the bodies in this cloud replenish and keep constant the number of long-period comets entering the inner Solar System—where they are eventually consumed and destroyed during close approaches to the Sun.
Positions of the main asteroid belt, Kuiper belt, and the Oort cloud in the Solar System. The current definition was included in the 2006 IAU resolution that defined the term planet, demoting the status of Pluto to that of dwarf planet.
The Oort Cloud is not gravitationally attracted enough to the Sun to form into a fairly thin disk, like the inner Solar System. Thus, comets originating from the Oort Cloud can come from roughly any orientation (inclination to the ecliptic), and many even have a retrograde orbit.
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). [42] Two TNOs have been visited and studied at close range, Pluto and 486958 Arrokoth.
C/2014 UN 271 came from the Oort cloud and has been inside of the orbit of Neptune (29.9 AU) since March 2014 and passed inside the orbit of Uranus (18.3 AU) in September 2022. [k] [16] [40] The time of perihelion has been well-known since June 2021. [6] The current 3-sigma uncertainty in the comet's distance from the Sun is ±35,000 km. [16]
Numerous such comets have been observed when close to the Sun. The closer an object is to the Sun the faster it needs to move to maintain the orbit. Objects move slowest when furthest from the Sun (aphelion) and fastest when closest to the Sun (perihelion) and this is why Oort cloud comets spend most of their time in the Oort cloud.
Simulations indicate that it has most likely come from the Oort cloud, with a roughly equal probability of being an extinct comet and a rocky body that was originally scattered into the Oort cloud. The discovery of 1996 PW prompted theoretical research that suggests that roughly 1 to 2 percent of the Oort cloud objects are rocky. [2] [10]