This article is about the outer Oort cloud. For the inner Oort cloud, see Hills cloud.
The distance from the Oort cloud to the interior of the Solar System, and two of the nearest stars, is measured in astronomical units. The scale is logarithmic: each indicated distance is ten times farther out than the previous distance. The red arrow indicates the location of the space probe Voyager 1 by 2012–2013, which will reach the Oort cloud in about 300 years.
An artist's impression of the Oort cloud and the Kuiper belt (inset); the sizes of objects are over-scaled for visibility.
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 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.[5]
The cloud is thought to comprise two regions: a disc-shaped inner Oort cloud aligned with the solar ecliptic (also called its Hills cloud) and a spherical outer Oort cloud enclosing the entire Solar System. Both regions lie well beyond the heliosphere and are in interstellar space.[4][6] The innermost portion of the Oort cloud is more than a thousand times as distant from the Sun than the Kuiper belt, the scattered disc and the detached objects—three nearer reservoirs of trans-Neptunian objects.
The outer limit of the Oort cloud defines the cosmographic boundary of the Solar System. This area is defined by the Sun's Hill sphere, and hence lies at the interface between solar and galactic gravitational dominion.[7] The outer Oort cloud is only loosely bound to the Solar System and its constituents are easily affected by the gravitational pulls of both passing stars and the Milky Way itself. These forces served to moderate and render more circular the highly eccentric orbits of material ejected from the inner Solar System during its early phases of development. The circular orbits of material in the Oort disc are largely thanks to this galactic gravitational torquing.[8] By the same token, galactic interference in the motion of Oort bodies occasionally dislodges comets from their orbits within the cloud, sending them into the inner Solar System.[4] Based on their orbits, most but not all of the short-period comets appear to have come from the Oort disc. Other short-period comets may have originated from the far larger spherical cloud.[4][9]
Astronomers hypothesize that the material presently in the Oort cloud formed much closer to the Sun, in the protoplanetary disc, and was then scattered far into space through the gravitational influence of the giant planets.[4] No direct observation of the Oort cloud is possible with present imaging technology.[10] Nevertheless, the cloud is thought to be the source that replenishes most long-period and Halley-type comets, which are eventually consumed by their close approaches to the Sun after entering the inner Solar System. The cloud may also serve the same function for many of the centaurs and Jupiter-family comets.[9]
Types of distant minor planets
Centaurs
Neptune trojans
Trans-Neptunian objects (TNOs)
Kuiper belt objects (KBOs)
Classical KBOs (cubewanos)
Resonant KBOs
Plutinos (2:3 resonance)
Twotinos (1:2 resonance)
Scattered disc objects (SDOs)
Resonant SDOs
Extreme trans-Neptunian object
Detached objects
Sednoids
Oort cloud objects (ICO/OCOs)
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^"Oort". Oxford English Dictionary (Online ed.). Oxford University Press. (Subscription or participating institution membership required.)
^Cite error: The named reference Whipple was invoked but never defined (see the help page).
^Williams, Matt (August 10, 2015). "What is the Oort Cloud?". Archived from the original on January 23, 2018. Retrieved May 21, 2021.
^ abcdeCite error: The named reference Morbidelli2006 was invoked but never defined (see the help page).
^Redd, Nola Taylor (October 4, 2018). "Oort Cloud: The Outer Solar System's Icy Shell". Space.com. Archived from the original on January 26, 2021. Retrieved August 18, 2020.
^Cite error: The named reference jpl.PIA17046 was invoked but never defined (see the help page).
^Cite error: The named reference NASA_SSE_oort was invoked but never defined (see the help page).
^Raymond, Sean (2023-06-21). "Oort cloud (exo)planets". PLANETPLANET. Archived from the original on 2023-07-01. Retrieved 2023-07-01.
^ abCite error: The named reference emel2007 was invoked but never defined (see the help page).
^"Oort Cloud". NASA Solar System Exploration. Archived from the original on 2023-06-30. Retrieved 2023-07-01.
Cite error: There are <ref group=note> tags on this page, but the references will not show without a {{reflist|group=note}} template (see the help page).
The Oortcloud (/ɔːrt, ʊərt/), sometimes called the Öpik–Oortcloud, is theorized to be a vast cloud of icy planetesimals surrounding the Sun at distances...
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interstellar space. The outermost region of the Solar System is the theorized Oortcloud, the source for long-period comets, extending 2,000–200,000 astronomical...
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astronomers consider the sednoids to be inner Oortcloud objects (OCOs), though the inner Oortcloud, or Hills cloud, was originally predicted to lie beyond...
together with the members of the scattered disc and any potential Hills cloud or Oortcloud objects, are collectively referred to as trans-Neptunian objects...
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Current models of Oortcloud formation predict that more comets are ejected into interstellar space than are retained in the Oortcloud, with estimates...
effect on Kuiper Belt formation. Tyche, a hypothetical planet in the OortCloud supposedly responsible for producing the statistical excess in long period...
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of Pluto. In 1950 Jan Oort suggested the presence of a cometary reservoir in the outer limits of the Solar System, the Oortcloud, and in 1951 Gerard Kuiper...
for well-known dwarf planets, minor planets and probable dwarf planets: Oortcloud comets can take 10+ years going from Neptune's orbit at 30.1 AU (4.50 billion km)...
enough to the Sun that it penetrated deep into the OortCloud and disturbed the population of OortCloud bodies and long-period comets there. Its mass is...
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