Detached object (astronomy)

Detached objects are nonclassical trans-Neptunian objects (TNOs) with a perihelion too far away from Neptune to be significantly influenced by it, and so appear to be “detached” from the solar system.cite journal | author= P. S. Lykawka; T. Mukai | title=An Outer Planet Beyond Pluto and the Origin of the Trans-Neptunian Belt Architecture | journal=Astronomical Journal | year = 2008 | volume=135 | pages=1161 | doi=10.1088/0004-6256/135/4/1161 | url=http://arxiv.org/pdf/0712.2198| id=arXiv|0712.2198 ] D.Jewitt, A.Delsanti "The Solar System Beyond The Planets" in "Solar System Update : Topical and Timely Reviews in Solar System Sciences ", Springer-Praxis Ed., ISBN 3-540-26056-0 (2006) [http://www.ifa.hawaii.edu/faculty/jewitt/papers/2006/DJ06.pdf Preprint of the article (pdf)] ] They have also been referred to as extended scattered disc objects (E-SDO), [http://www.obs-nice.fr/gladman/cr105.html "Evidence for an Extended Scattered Disk?"] ] Distant Detached Objects (DDO)cite journal|url=http://adsabs.harvard.edu/abs/2006Icar..184..589G
title=A distant planetary-mass solar companion may have produced distant detached objects|author=Rodney S. Gomes|coauthors= John J. Matese, Jack J. Lissauer|journal=Icarus|volume=184|issue=2|year=2006|pages=589–601|publisher=Elsevier |doi=10.1016/j.icarus.2006.05.026] or Scattered-Extended in the formal classification by Deep Ecliptic Survey.cite journal|author=J. L. Elliot, S. D. Kern, K. B. Clancy, A. A. S. Gulbis, R. L. Millis, M. W. Buie, L. H. Wasserman, E. I. Chiang, A. B. Jordan, D. E. Trilling, and K. J. Meech| title=The Deep Ecliptic Survey: A Search for Kuiper Belt Objects and Centaurs. II. Dynamical Classification, the Kuiper Belt Plane, and the Core Population|journal=The Astronomical Journal| volume=129| year=2006| url=http://alpaca.as.arizona.edu/~trilling/des2.pdf|formal=preprint] A total of nine such bodies have been securely identified.cite journal|author=Lykawka, Patryk Sofia & Mukai, Tadashi|year=2007| title= Dynamical classification of trans-neptunian objects: Probing their origin, evolution, and interrelation|journal = Icarus|volume=189|issue=1|month=July |pages=213-232| doi=10.1016/j.icarus.2007.01.001]

Orbits

Detached objects generally have highly elliptical, very large orbits with semi-major axes of up to a few hundred AU. Such orbits cannot have been created by gravitational scattering by the gas giants (in particular, Neptune). Instead, a number of explanations have been put forward, including an encounter with a passing starcite journal|journal=The Astronomical Journal|issue=5|volume=128 |pages=2564–2576|year=2004 |month=November|title=Scenarios for the Origin of the Orbits of the Trans-Neptunian Objects mp|2000 CR|105 and mp|2003 VB|12|first=Alessandro|last=Morbidelli|coauthors=Harold F. Levison|url= http://www.iop.org/EJ/abstract/1538-3881/128/5/2564/|doi=10.1086/424617 |accessdate=2008-07-02 ] or a distant, planet-sized object.cite journal|url= http://adsabs.harvard.edu/abs/2006Icar..184..589G|title=A distant planetary-mass solar companion may have produced distant detached objects|first=Rodney S. |last=Gomes|coauthors= John J. Matese, and Jack J. Lissauer |journal=Icarus|volume=184|issue=2|pages=589–601|year=2006|month=October|doi=10.1016/j.icarus.2006.05.026 |accessdate=2008-07-02] The classification suggested by the Deep Ecliptic Survey team introduces a formal distinction between "Scattered-Near" objects (which could be scattered by Neptune) and "Scattered-Extended" objects (e.g. 90377 Sedna) using a Tisserand's parameter value of 3.cite journal|author=J. L. Elliot, S. D. Kern, K. B. Clancy, A. A. S. Gulbis, R. L. Millis, M. W. Buie, L. H. Wasserman, E. I. Chiang, A. B. Jordan, D. E. Trilling, and K. J. Meech|title=The Deep Ecliptic Survey: A Search for Kuiper Belt Objects and Centaurs. II. Dynamical Classification, the Kuiper Belt Plane, and the Core Population|journal=The Astronomical Journal|volume=129|year=2006|url=http://alpaca.as.arizona.edu/~trilling/des2.pdf|format=preprint]

Classification

Detached objects are one of four distinct dynamical classes of TNO; the other three classes are classical Kuiper belt objects, resonant objects and scattered disc objects (SDO). Detached objects generally have a perihelion distance greater than 40 astronomical units (AU). However, there are no clear boundaries between the scattered and detached regions, since both can coexist as TNOs in an intermediate region with perihelion distance between 37 and 40 AU.

The discovery of 90377 Sedna together with a few other objects such as mpl|2000 CR|105 and mpl|2004 XR|190 (also known as "Buffy") has motivated discussion of a category of distant objects that may also be inner Oort cloud objects or (more likely) transitional objects between the scattered disc and the inner Oort cloud.

Although Sedna is officially considered a scattered disc object 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 disc.cite web
title=Sedna (The coldest most distant place known in the solar system; possibly the first object in the long-hypothesized Oort cloud)
last=Brown
first=Michael E.
authorlink=Michael E. Brown
publisher=California Institute of Technology, Department of Geological Sciences
url=http://www.gps.caltech.edu/~mbrown/sedna/
accessdate=2008-07-02] This line of thinking suggests that a lack of gravitational interaction with the outer planets disqualifies a trans-neptunian object from scattered disc membership, which would create an outer edge somewhere between Sedna and more conventional SDOs like Eris.

Known members

References