Scattered disc

From Freepedia

The scattered disc (or scattered disk) is a distant region of our solar system, thinly populated by icy planetoids known as scattered disk objects (SDOs), a subset of the broader family of trans-Neptunian objects (TNOs). The innermost portion of the scattered disc overlaps with the Kuiper belt, but its outer limits extend much farther away from the sun and above and below the ecliptic than the belt proper.

The scattered disk is still fairly poorly understood, although prevailing astronomical opinion suggests it was formed when Kuiper belt objects (KBOs) were "scattered" by gravitational interactions with the outer planets, principally Neptune, into highly-eccentric and -inclined orbits. While the Kuiper belt is a relatively "round" and "flat" doughnut of space extending from about 30 AU to 44 AU with its member-objects locked in autonomously circular orbits (cubewanos) or mildly-eliptical resonant orbits (plutinos and twotinos), the scattered disc is by comparison a much more erratic millieu. SDOs can often, as in the case of 2003 UB₃₁₃, travel almost as great a "vertical" distance they do relative to what has come to be defined as "horizontal." Orbital simulations show SDO orbits may well be erratic and unstable and that the ultimate fate of these objects is to be permanently ejected from the core of the solar system into the Oort cloud or beyond.

There is an emerging sense that centaurs may simply be objects just like SDOs that were knocked inwards from the Kuiper belt rather than outwards, making them simply "non-trans-Neptunian" SDOs [1]. Indeed, some objects like (29981) 1999 TD₁₀ blur the distinction, and the Minor Planet Center (MPC) now lists centaurs and SDOs together [2]. In recognition of this blurring of categorization, some scientists use "scattered kuiper belt object" (or SKBO) as an umbrella term for both centaurs and member bodies of the scattered disc.

TNOs and similar bodies
Non-trans-Neptunian objects Centaurs Trans-Neptunian objects (TNOs) Kuiper belt objects (KBOs) cubewanos (classical KBOs) plutinos (3:2 resonant KBOs) twotinos (2:1 resonant KBOs) Scattered disc objects (SDOs) Oort cloud objects (OCOs)

Although the TNO 90377 Sedna is officially considered an SDO by the MPC, its discoverer Michael E. Brown has suggested that because its perihelion distance of 76 AU is too distant to be affected by the gravitational attraction of the outer planets it should be considered an inner Oort cloud object rather than a member of the scattered disk [3]. This line of thinking suggests that a lack of gravitational interaction with the outer planets disqualifies a TNO from scattered disc membership, which would create an outer edge somewhere between Sedna and more conventional SDOs like 2003 UB₃₁₃. If Sedna is beyond the scattered disk, it may not be not unique; 2000 CR₁₀₅, which was discovered before Sedna, may also be an inner Oort cloud object or (more likely) a transitional object between the scattered disc and the inner Oort cloud.

Scattered disk objects

The first SDO to be discovered was (15874) 1996 TL₆₆, first identified in 1996 by astronomers based at Mauna Kea.

List of Notable SDOs

Permanent Designation	Provisional Designation	Absolute magnitude	Albedo	Equatorial diameter (km)	Semimajor axis (AU)	Date discovered	Discoverer	Diameter method
	2003 UB₃₁₃	−1.1	0.6 (assumed)	~3000 (> 2300)	67.7	2005	M. Brown, C. Trujillo & D. Rabinowitz	assumed albedo
84522	2002 TC₃₀₂	3.9	> 0.03	< 1211	55.1	2002	NEAT	thermal
15874	1996 TL₆₆	5.4	0.10	<958 km	82.9	1996	D. Jewett, J. Luu & J. Chen	assumed albedo