سحابة هيلز

Artist's view of the Oort cloud, Hills cloud, and Kuiper belt (inset)

In astronomy, the Hills cloud (also called the inner Oort cloud^[1] and inner cloud^[2]) is a vast theoretical circumstellar disc, interior to the Oort cloud, whose outer border would be located at around 20,000 to 30,000 astronomical units (AU) from the Sun, and whose inner border, less well defined, is hypothetically located at 250–1500 AU,^{[بحاجة لمصدر]} well beyond planetary and Kuiper Belt object orbits—but distances might be much greater. If it exists, the Hills cloud contains roughly 5 times as many comets as the Oort cloud.^[3]

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Overview

History

Original Oort cloud model

Ernst Öpik

New model

Jack G. Hills, the astronomer who first proposed the Hills cloud

Characteristics

Structure and composition

Interior and exterior Oort cloud

Formation

Possible Hills cloud objects

Name	Diameter (km)	Perihelion (AU)	Aphelion (AU)	Discovery
2012 VP₁₁₃	315 to 640	80٫5	445	2012
(90377) Sedna	995 to 1٬060	76٫1	935	2003
(87269) 2000 OO₆₇	28 to 87	20٫8	1,014.2	2000
(308933) 2006 SQ₃₇₂	50 to 100	24٫17	2,005.38	2006

Comets

Comet McNaught

Sedna, the first candidate

Animation of Sedna's orbit (in red) with the Hills cloud (in blue) at the last moment of the loop

Artist's impression of Sedna

2012 VP₁₁₃

Trans-Neptunian object 2012 VP₁₁₃ was announced on 26 March 2014 and has a similar orbit to Sedna with a perihelion point significantly detached from Neptune. Its orbit lies between 80 and 400 AU from the Sun.

الهوامش

المصادر

^ see Oort cloud
^ Villemin, Gérard. "Astronomie, astéroïdes et comètes" (in الفرنسية).
^ Duncan, Martin J.; Quinn, Thomas; Tremaine, Scott (1987). "The Formation and Extent of the Solar System Comet Cloud". The Astronomical Journal. 94: 1330. Bibcode:1987AJ.....94.1330D. doi:10.1086/114571.

قراءات إضافية

Heisler, Julia; Tremaine, Scott (1986). "The influence of the galactic tidal field on the Oort comet cloud". Icarus. 65 (1): 13. Bibcode:1986Icar...65...13H. doi:10.1016/0019-1035(86)90060-6.
Dones, Luke; Weissman, Paul R.; Levison, Harold F.; Duncan, Martin J. (2004). "Oort cloud formation and dynamics" (PDF). In Johnstone, Doug; Adams, Fred C.; Lin, Doug N. C.; Neufeld, David A.; Ostriker, Eve C. (eds.). Star Formation in the Interstellar Medium: In Honor of David Hollenbach, Chris McKee, and Frank Shu. ASP Conference Proceedings. Vol. 323. San Francisco, CA: Astronomical Society of the Pacific. p. 371. Bibcode:2004ASPC..323.....J.