Editing Oort cloud (section)

== Origin ==
The Oort cloud is thought to have developed after the [[Formation and evolution of the Solar System|formation of planets]] from the primordial [[protoplanetary disc]] approximately 4.6&nbsp;billion years ago.<ref name=Morbidelli2006 /> 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 [[planet]]s and [[minor planet]]s. After formation, strong gravitational interactions with young gas giants, such as Jupiter, scattered the objects into extremely wide [[Elliptic orbit|elliptical]] or [[parabolic orbit]]s that were subsequently modified by perturbations from passing stars and giant molecular clouds into long-lived orbits detached from the gas giant region.<ref name=Morbidelli2006 /><ref>{{cite web
 |title=Oort Cloud & Sol b?
 |url=http://www.solstation.com/stars/oort.htm
 |publisher=SolStation
 |access-date=2007-05-26
 |archive-date=2020-02-14
 |archive-url=https://web.archive.org/web/20200214082923/http://www.solstation.com/stars/oort.htm
 |url-status=live
 }}</ref>

Recent research has been cited by NASA hypothesizing that a large number of Oort cloud objects are the product of an exchange of materials between the Sun and its sibling stars as they formed and drifted apart and it is suggested that many—possibly the majority—of Oort cloud objects did not form in close proximity to the Sun.<ref name="nasax" /> Simulations of the evolution of the Oort cloud from the beginnings of the Solar System to the present suggest that the cloud's mass peaked around 800&nbsp;million years after formation, as the pace of accretion and collision slowed and depletion began to overtake supply.<ref name=Morbidelli2006 />

Models by [[Julio Ángel Fernández]] suggest that the [[scattered disc]], which is the main source for [[periodic comet]]s in the Solar System, might also be the primary source for Oort cloud objects. According to the models, about half of the objects scattered travel outward toward the Oort cloud, whereas a quarter are shifted inward to Jupiter's orbit, and a quarter are ejected on [[Hyperbola|hyperbolic]] orbits. The scattered disc might still be supplying the Oort cloud with material.<ref>{{cite journal | last = Fernández | first = Julio A. | title = The Formation of the Oort Cloud and the Primitive Galactic Environment | journal = Icarus | volume = 129 | issue = 1 | pages = 106–119 | year = 1997 | doi = 10.1006/icar.1997.5754 | bibcode = 1997Icar..129..106F | url = https://www.sciencedirect.com/science/article/abs/pii/S0019103597957547 }}</ref><ref>{{cite journal
 |author=Julio A. Fernández
 |author2=Tabaré Gallardo
 |author3=Adrián Brunini
 |name-list-style=amp
 |date=2004
 |title=The scattered disc population as a source of Oort Cloud comets: evaluation of its current and past role in populating the Oort Cloud
 |journal=[[Icarus (journal)|Icarus]]
 |volume=172 |issue=2  |pages=372–381
 |bibcode=2004Icar..172..372F
 |doi=10.1016/j.icarus.2004.07.023
|hdl=11336/36810
 |hdl-access=free
 }}</ref> A third of the scattered disc's population is likely to end up in the Oort cloud after 2.5&nbsp;billion years.<ref>{{cite book
 |author=Davies, J. K.
 |author2=Barrera, L. H.
 |date=2004
 |title=The First Decadal Review of the Edgeworth-Kuiper Belt.
 |url=https://books.google.com/books?id=WuDdVbJf_d8C&q=+oort+cloud&pg=PA43
 |publisher=Kluwer Academic Publishers
 |isbn=978-1-4020-1781-0
 |access-date=2020-10-11
 |archive-date=2021-03-06
 |archive-url=https://web.archive.org/web/20210306212708/https://books.google.com/books?id=WuDdVbJf_d8C&q=+oort+cloud&pg=PA43
 |url-status=live
 }}</ref>

Computer models suggest that collisions of cometary debris during the formation period play a far greater role than was previously thought. According to these models, the number of collisions early in the Solar System's history was so great that most comets were destroyed before they reached the Oort cloud. Therefore, the current cumulative mass of the Oort cloud is far less than was once suspected.<ref>{{cite journal
 |author=S. Alan Stern
 |author2=Paul R. Weissman
 |date=2001
 |title=Rapid collisional evolution of comets during the formation of the Oort Cloud
 |journal=[[Nature (journal)|Nature]]
 |volume=409 |issue=6820 |pages=589–591
 |bibcode=2001Natur.409..589S
 |doi=10.1038/35054508
 |pmid=11214311
|s2cid=205013399
 }}</ref> The estimated mass of the cloud is only a small part of the 50–100 Earth masses of ejected material.<ref name=Morbidelli2006 />

Gravitational interaction with nearby stars and [[galactic tide]]s modified cometary orbits to make them more circular. This explains the nearly spherical shape of the outer Oort cloud.<ref name=Morbidelli2006 /> On the other hand, the [[Hills cloud]], which is bound more strongly to the Sun, has not acquired a spherical shape. Recent studies have shown that the formation of the Oort cloud is broadly compatible with the hypothesis that the [[Solar System]] formed as part of an embedded [[star cluster|cluster]] of 200–400 stars. These early stars likely played a role in the cloud's formation, since the number of close stellar passages within the cluster was much higher than today, leading to far more frequent perturbations.<ref>{{cite journal
 |author=R. Brasser
 |author2=M. J. Duncan
 |author3=H.F. Levison
 |date=2006
 |title=Embedded star clusters and the formation of the Oort Cloud
 |journal=[[Icarus (journal)|Icarus]]
 |volume=184 |issue=1 |pages=59–82
 |bibcode=2006Icar..184...59B
 |doi=10.1016/j.icarus.2006.04.010
}}</ref>

In June 2010 [[Harold F. Levison]] and others suggested on the basis of enhanced computer simulations that the Sun "captured comets from other stars while it was in its [[open cluster|birth cluster]]." Their results imply that "a substantial fraction of the Oort cloud comets, perhaps exceeding 90%, are from the protoplanetary discs of other stars."<ref>{{cite journal | author1 =Levison, Harold | title =Capture of the Sun's Oort Cloud from Stars in Its Birth Cluster | journal =Science | volume =329 | issue =5988 | pages =187–190 | date =10 June 2010 | doi =10.1126/science.1187535|bibcode = 2010Sci...329..187L |display-authors=etal | pmid=20538912| s2cid =23671821 | doi-access =free }}</ref><ref>{{cite web | title =Many famous comets originally formed in other solar systems | work =Southwest Research Institute® (SwRI®) News | date =10 June 2010 | url =http://www.swri.org/9what/releases/2010/cometorigins.htm | url-status =dead | archive-url =https://web.archive.org/web/20130527002420/http://www.swri.org/9what/releases/2010/cometorigins.htm | archive-date =27 May 2013 }}</ref> In July 2020 Amir Siraj and [[Avi Loeb]] found that a captured origin for the Oort Cloud in the Sun's [[Open cluster|birth cluster]] could address the theoretical tension in explaining the observed ratio of outer Oort cloud to [[scattered disc]] objects, and in addition could increase the chances of a captured [[Planet Nine]].<ref>{{Cite journal|last1=Brasser|first1=R.|last2=Morbidelli|first2=A.|date=2013-07-01|title=Oort cloud and Scattered Disc formation during a late dynamical instability in the Solar System|url=http://www.sciencedirect.com/science/article/pii/S001910351300122X|journal=Icarus|language=en|volume=225|issue=1|pages=40–49|doi=10.1016/j.icarus.2013.03.012|issn=0019-1035|arxiv=1303.3098|bibcode=2013Icar..225...40B|s2cid=118654097|access-date=2020-11-16|archive-date=2021-03-06|archive-url=https://web.archive.org/web/20210306202733/https://www.sciencedirect.com/science/article/abs/pii/S001910351300122X|url-status=live}}</ref><ref>{{Cite journal|last1=Siraj|first1=Amir|last2=Loeb|first2=Abraham|date=2020-08-18|title=The Case for an Early Solar Binary Companion|journal=The Astrophysical Journal|language=en|volume=899|issue=2|pages=L24|doi=10.3847/2041-8213/abac66|issn=2041-8213|arxiv=2007.10339|bibcode=2020ApJ...899L..24S|s2cid=220665422 |doi-access=free }}</ref><ref>{{Cite web|date=2020-08-17|title=The Sun May Have Started Its Life with a Binary Companion|url=https://www.cfa.harvard.edu/news/2020-19|access-date=2020-11-16|website=www.cfa.harvard.edu/|language=en|archive-date=2021-03-02|archive-url=https://web.archive.org/web/20210302150612/https://www.cfa.harvard.edu/news/2020-19|url-status=live}}</ref>