Detached object (astronomy) - AbsoluteAstronomy.com

Detached objects are a dynamical class of bodies in the outer Solar System

Solar System

The Solar System consists of the Sun and the astronomical objects gravitationally bound in orbit around it, all of which formed from the collapse of a giant molecular cloud approximately 4.6 billion years ago. The vast majority of the system's mass is in the Sun...

beyond the orbit of Neptune

Neptune

Neptune is the eighth and farthest planet from the Sun in the Solar System. Named for the Roman god of the sea, it is the fourth-largest planet by diameter and the third largest by mass. Neptune is 17 times the mass of Earth and is slightly more massive than its near-twin Uranus, which is 15 times...

. These objects have orbits whose points of closest approach to the Sun (perihelion

Apsis

An apsis , plural apsides , is the point of greatest or least distance of a body from one of the foci of its elliptical orbit. In modern celestial mechanics this focus is also the center of attraction, which is usually the center of mass of the system...

) are sufficiently distant from the gravitational influence

Gravitational two-body problem

For further relevant mathematical developments see also Two-body problem, also Kepler orbit, and Kepler problem, and Equation of the center – Analytical expansions...

of Neptune that they are essentially unaffected by Neptune and the other planets: this makes them appear to be "detached" from the Solar System.

In this way, they differ substantially from the majority of the known trans-Neptunian object

Trans-Neptunian object

A trans-Neptunian object is any minor planet in the Solar System that orbits the Sun at a greater distance on average than Neptune.The first trans-Neptunian object to be discovered was Pluto in 1930...

s (TNOs), which form a loosely defined set of populations that have been perturbed

Perturbation (astronomy)

Perturbation is a term used in astronomy in connection with descriptions of the complex motion of a massive body which is subject to appreciable gravitational effects from more than one other massive body....

to varying degrees onto their current orbit by gravitational encounters with the gas giant

Gas giant

A gas giant is a large planet that is not primarily composed of rock or other solid matter. There are four gas giants in the Solar System: Jupiter, Saturn, Uranus, and Neptune...

s, predominantly Neptune. Detached objects have larger perihelia than these other TNO populations, including the objects in orbital resonance

Orbital resonance

In celestial mechanics, an orbital resonance occurs when two orbiting bodies exert a regular, periodic gravitational influence on each other, usually due to their orbital periods being related by a ratio of two small integers. Orbital resonances greatly enhance the mutual gravitational influence of...

with Neptune, such as Pluto

Pluto

Pluto, formal designation 134340 Pluto, is the second-most-massive known dwarf planet in the Solar System and the tenth-most-massive body observed directly orbiting the Sun...

, the classical Kuiper belt objects in non-resonant orbits such as Makemake, and the scattered disk objects like Eris

Eris (dwarf planet)

Eris, formal designation 136199 Eris, is the most massive known dwarf planet in the Solar System and the ninth most massive body known to orbit the Sun directly...

.

Detached objects have also been referred to in the scientific literature as extended scattered disc objects (E-SDO), distant detached objects (DDO), or scattered–extended, as in the formal classification by the Deep Ecliptic Survey

Deep Ecliptic Survey

The Deep Ecliptic Survey is a project to find Kuiper belt objects , using the facilities of the National Optical Astronomy Observatory .The principal investigator is Bob Millis....

. This reflects the dynamical gradation that can exist between the orbital parameters of the scattered disk and the detached population.

At least nine such bodies have been securely identified, of which the largest, most distant, and best known is Sedna

90377 Sedna

90377 Sedna is a trans-Neptunian object discovered in 2003, which was about three times as far from the Sun as Neptune. For most of its orbit it is even further from the Sun, with its aphelion estimated at 960 astronomical units , making it one of the most distant known objects in the Solar System...

Orbits

Detached objects have perihelia much larger than Neptune's aphelion. They often have highly elliptical

Ellipse

In geometry, an ellipse is a plane curve that results from the intersection of a cone by a plane in a way that produces a closed curve. Circles are special cases of ellipses, obtained when the cutting plane is orthogonal to the cone's axis...

, very large orbits with semi-major axes

Semi-major axis

The major axis of an ellipse is its longest diameter, a line that runs through the centre and both foci, its ends being at the widest points of the shape...

of up to a few hundred astronomical unit

Astronomical unit

An astronomical unit is a unit of length equal to about or approximately the mean Earth–Sun distance....

s (AU, the radius of Earth's orbit). Such orbits cannot have been created by gravitational scattering

Perturbation (astronomy)

by the gas giants

Gas Giants

Gas Giants were a pop rock band from Tempe, Arizona, formed as a successor project to the Gin Blossoms. The group was known as The Pharaohs when they formed in 1997, but changed their name after their label, A&M Records, merged with Universal Records and the band changed hands, re-signing with...

(in particular, Neptune). Instead, a number of explanations have been put forward, including an encounter with a passing star or a distant planet-sized object. The classification suggested by the Deep Ecliptic Survey

Deep Ecliptic Survey

The Deep Ecliptic Survey is a project to find Kuiper belt objects , using the facilities of the National Optical Astronomy Observatory .The principal investigator is Bob Millis....

team introduces a formal distinction between scattered-near objects (which could be scattered by Neptune) and scattered-extended objects (e.g. 90377 Sedna

90377 Sedna

) using a Tisserand's parameter

Tisserand's parameter

Tisserand's parameter is a combination of orbital elements used in a restricted three-body problem.-Definition:...

value of 3.

Classification

Detached objects are one of four distinct dynamical classes of TNO; the other three classes are classical Kuiper-belt objects, resonant object

Resonant trans-Neptunian object

In astronomy, a resonant trans-Neptunian object is a trans-Neptunian object in mean motion orbital resonance with Neptune. The orbital periods of the resonant objects are in a simple integer relations with the period of Neptune e.g. 1:2, 2:3 etc...

s and scattered-disc objects

Scattered disc

The scattered disc is a distant region of the Solar System that is sparsely populated by icy minor planets, a subset of the broader family of trans-Neptunian objects. The scattered-disc objects have orbital eccentricities ranging as high as 0.8, inclinations as high as 40°, and perihelia greater...

(SDO). Detached objects generally have a perihelion distance greater than 40 AU, deterring strong interactions with Neptune, which has an approximately circular orbit ca. 30AU from the Sun. 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. One such intermediate body with a well determined orbit is .

The discovery of 90377 Sedna

90377 Sedna

together with a few other objects such as and (also known as "Buffy") has motivated discussion of a category of distant objects that may also be inner Oort cloud

Oort cloud

The Oort cloud , or the Öpik–Oort cloud , is a hypothesized spherical cloud of comets which may lie roughly 50,000 AU, or nearly a light-year, from the Sun. This places the cloud at nearly a quarter of the distance to Proxima Centauri, the nearest star to the Sun...

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

Michael E. Brown

Michael E. Brown has been a professor of planetary astronomy at the California Institute of Technology since 2003....

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. This classification of Sedna as a detached object is accepted in recent publications.

This line of thinking suggests that the lack of a significant gravitational interaction

Perturbation (astronomy)

with the outer planets creates an extended–outer group starting somewhere between Sedna (perihelion 76AU) and more conventional SDOs like (perihelion 35AU), which is listed as a scattered–near object by the Deep Ecliptic Survey.

One of the problems with defining this extended category is that weak resonances may exist and would be difficult to prove due to chaotic planetary perturbations and the current lack of accuracy in the orbits of these distant objects. These objects have orbital period

Orbital period

The orbital period is the time taken for a given object to make one complete orbit about another object.When mentioned without further qualification in astronomy this refers to the sidereal period of an astronomical object, which is calculated with respect to the stars.There are several kinds of...

s of more than 300 years and most have only been observed over a short observation arc

Arc (geometry)

In geometry, an arc is a closed segment of a differentiable curve in the two-dimensional plane; for example, a circular arc is a segment of the circumference of a circle...

of a couple years. Due to their great distance and slow movement against background stars, it may be decades before most of these distant orbits are determined well enough to confidently confirm or rule out a resonance. Further improvement in the orbit and potential resonance of these objects will help to understand the migration of the giant planets and the formation of the Solar System. For example simulations by Emel’yanenko and Kiseleva in 2007 show that many distant objects could be in resonance with Neptune

Resonant trans-Neptunian object

. They show a 10% likelihood that 2000 CR₁₀₅ is in a 20:1 resonance, a 38% likelihood that 2003 QK₉₁ is in a 10:3 resonance, and a 84% likelihood that is in a 8:3 resonance. The dwarf-planet candidate appears to have less than a 1% likelihood of being in a 4:1 resonance.

Candidates

This is a list of known objects by decreasing perihelion

Apsis

, that could not be easily scattered by Neptune's current orbit and therefore are likely to be detached objects:

Designation number	Name	Diameter (km)	H	Perihelion Apsis An apsis , plural apsides , is the point of greatest or least distance of a body from one of the foci of its elliptical orbit. In modern celestial mechanics this focus is also the center of attraction, which is usually the center of mass of the system... (AU)	Aphelion Apsis An apsis , plural apsides , is the point of greatest or least distance of a body from one of the foci of its elliptical orbit. In modern celestial mechanics this focus is also the center of attraction, which is usually the center of mass of the system... (AU)	Year discovered	Discoverer(s)	Method of diameter calculation	Type
90377	Sedna 90377 Sedna 90377 Sedna is a trans-Neptunian object discovered in 2003, which was about three times as far from the Sun as Neptune. For most of its orbit it is even further from the Sun, with its aphelion estimated at 960 astronomical units , making it one of the most distant known objects in the Solar System...	1200–1600	1.6	76.1	975.5	2003	Brown Michael E. Brown Michael E. Brown has been a professor of planetary astronomy at the California Institute of Technology since 2003.... , Trujillo Chad Trujillo Chadwick A. "Chad" Trujillo is an astronomer and the co-discoverer of the dwarf planet Eris.Trujillo works with computer software and has examined the orbits of the numerous trans-Neptunian objects , which is the outer area of the solar system that he specialized in. In late August 2005, it was... , Rabinowitz David L. Rabinowitz David Lincoln Rabinowitz is a researcher at Yale University. He has built CCD cameras and software for the detection of near-Earth asteroids and Kuiper Belt Objects, and his research has helped reduce the assumed number of near-Earth asteroids by half, from 1,000-2,000 to 500-1,000 He has also...	thermal	detached
		335–850	4.5	52.3	61.8	2004	Lynne Jones et al.	assumed	detached
		130–300	6.4	47.3	614	2004	CTIO	assumed	detached
145480	2005 TB₁₉₀ (145480) 2005 TB190 ', provisionally known as 2005 TB190, is a trans-Neptunian object with an absolute magnitude of 4.7. This qualifies it as a dwarf-planet candidate.-Orbit:...	~500	4.7	46.2	106.5	2005	Becker, A. C. et al.	assumed	detached
148209	2000 CR₁₀₅	~250	6.1	44.3	397	2000	Lowell Observatory Lowell Observatory Lowell Observatory is an astronomical observatory in Flagstaff, Arizona. Lowell Observatory was established in 1894, placing it among the oldest observatories in the United States, and was designated a National Historic Landmark in 1965....	assumed	detached
		~150	7.3	41.2	57.1	2003	Pittichova, J. et al.	assumed	classical?
82075	2000 YW₁₃₄ (82075) 2000 YW134 ', provisionally known as 2000 YW134, is a binary trans-Neptunian object . It is classified as a scattered disc object and, possibly, a detached object.- Physical characteristics :...	~500	4.7	41.0	73.9	2000	Spacewatch Spacewatch Spacewatch is a project at the University of Arizona led by Robert S. McMillan that specializes in the study of minor planets, including various types of asteroids and comets...	assumed	8:3 Resonant trans-Neptunian object In astronomy, a resonant trans-Neptunian object is a trans-Neptunian object in mean motion orbital resonance with Neptune. The orbital periods of the resonant objects are in a simple integer relations with the period of Neptune e.g. 1:2, 2:3 etc...
48639	1995 TL₈ (48639) 1995 TL8 ' is a detached trans-Neptunian object possessing a relatively large satellite....	~350	5.2	40.0	64.5	1995	A. Gleason	assumed	detached
		~180	6.9	38.4	98.5	2003	Elliot, J. et al.	assumed	detached
		~150	7.3	38.0	85.6	2003	Mauna Kea Mauna Kea Observatory The Observatories at Mauna Kea, , are an independent collection of astronomical research facilities located on the summit of Mauna Kea on the Big Island of Hawai'i, USA. The facilities are located in a special land use zone known as the "Astronomy Precinct," which is located in the Mauna Kea...	assumed	detached
134210	2005 PQ₂₁	~200	6.7	37.6	87.6	2005	Cerro Tololo	assumed	detached
		~765	3.8	37.6	97.0	2006	CTIO	assumed	detached or 5:1 Resonant trans-Neptunian object In astronomy, a resonant trans-Neptunian object is a trans-Neptunian object in mean motion orbital resonance with Neptune. The orbital periods of the resonant objects are in a simple integer relations with the period of Neptune e.g. 1:2, 2:3 etc... ?
120132	2003 FY₁₂₈ (120132) 2003 FY128 ', also written as 2003 FY128, is a trans-Neptunian object.-Detached:It is classified as a detached object by the Deep Ecliptic Survey since its orbit appears to be beyond the current control of Neptune...	~440	4.8	37.0	61.7	2003	N.E.A.T. Near Earth Asteroid Tracking Near-Earth Asteroid Tracking is a program run by NASA and Jet Propulsion Laboratory to discover near-Earth objects. The NEAT project began in December 1995 and ran until April 2007.-History:...	assumed	detached
		~290	5.9	36.4	102.6	2006	M. W. Buie Marc W. Buie Marc W. Buie is an astronomer at Lowell Observatory in Flagstaff, Arizona. He grew up in Baton Rouge, Louisiana and went on to get a B.S. in Physics from Louisiana State University in 1980. After that he switched fields and earned his Ph.D. in Planetary Science from the University of Arizona in...	assumed	detached or 7:2 Resonant trans-Neptunian object In astronomy, a resonant trans-Neptunian object is a trans-Neptunian object in mean motion orbital resonance with Neptune. The orbital periods of the resonant objects are in a simple integer relations with the period of Neptune e.g. 1:2, 2:3 etc... ?
		440–980	3.9	39.1	52.5	2010	A. Udalski et al.	assumed	detached or classical

Orbits

Classification

Candidates

See also