![InnerSolarSystem-en](https://upload.wikimedia.org/wikipedia/commons/f/f3/InnerSolarSystem-en.png)
A minor-planet group is a population of
minor planet
According to the International Astronomical Union (IAU), a minor planet is an astronomical object in direct orbit around the Sun that is exclusively classified as neither a planet nor a comet. Before 2006, the IAU officially used the term ''minor ...
s that share broadly similar orbits. Members are generally unrelated to each other, unlike in an
asteroid family
An asteroid family is a population of asteroids that share similar proper orbital elements, such as semimajor axis, eccentricity, and orbital inclination. The members of the families are thought to be fragments of past asteroid collisions. An a ...
, which often results from the break-up of a single asteroid. It is customary to name a group of asteroids after the first member of that group to be discovered, which is often the largest.
Groups out to the orbit of Earth
There are relatively few asteroids that orbit close to the Sun. Several of these groups are hypothetical at this point in time, with no members having yet been discovered; as such, the names they have been given are provisional.
*
Vulcanoid asteroids are hypothetical asteroids that orbit entirely within the orbit of
Mercury
Mercury commonly refers to:
* Mercury (planet), the nearest planet to the Sun
* Mercury (element), a metallic chemical element with the symbol Hg
* Mercury (mythology), a Roman god
Mercury or The Mercury may also refer to:
Companies
* Merc ...
(have an
aphelion
An apsis (; ) is the farthest or nearest point in the orbit of a planetary body about its primary body. For example, the apsides of the Earth are called the aphelion and perihelion.
General description
There are two apsides in any ellip ...
of less than 0.3874 AU). A few searches for vulcanoids have been conducted but none have been discovered so far.
*
ꞌAylóꞌchaxnim asteroids (previously named Vatira) are asteroids that orbit entirely within the orbit of
Venus
Venus is the second planet from the Sun. It is sometimes called Earth's "sister" or "twin" planet as it is almost as large and has a similar composition. As an interior planet to Earth, Venus (like Mercury) appears in Earth's sky never fa ...
(have an aphelion of less than 0.718 AU). , one such asteroid is known:
594913 ꞌAylóꞌchaxnim.
*
Atira asteroids (Apohele; Interior-Earth Objects) are a small group of known asteroids whose aphelion is less than 0.983 AU, meaning they orbit entirely within Earth's orbit. The group is named after its first confirmed member,
163693 Atira. , the group consists of 22 members, 6 of which are numbered.
*
Mercury-crosser asteroids having a
perihelion
An apsis (; ) is the farthest or nearest point in the orbit of a planetary body about its primary body. For example, the apsides of the Earth are called the aphelion and perihelion.
General description
There are two apsides in any ellip ...
smaller than Mercury's 0.3075 AU.
*
s having a perihelion smaller than
Venus
Venus is the second planet from the Sun. It is sometimes called Earth's "sister" or "twin" planet as it is almost as large and has a similar composition. As an interior planet to Earth, Venus (like Mercury) appears in Earth's sky never fa ...
's 0.7184 AU. This group includes the above Mercury-crossers (if their aphelion is greater than Venus's perihelion. All known Mercury crossers satisfy this condition except ꞌAylóꞌchaxnim, which has an aphelion smaller than Venus's perihelion and a perihelion slightly smaller than Mercury's aphelion).
*
Earth-crosser asteroid
An Earth-crosser is a near-Earth asteroid whose orbit crosses that of Earth as observed from the ecliptic pole of Earth's orbit. The known numbered Earth-crossers are listed here. Those Earth-crossers whose semi-major axes are smaller than E ...
s having a perihelion smaller than
Earth
Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surfa ...
's 0.9833 AU. This group includes the above Mercury- and Venus-crossers, apart from the Apoheles. They are also divided into the
**
Aten asteroid
The Aten asteroids are a dynamical group of asteroids whose orbits bring them into proximity with Earth. By definition, Atens are Earth-crossing asteroids . The group is named after 2062 Aten, the first of its kind, discovered on 7 January ...
s having a
semi-major axis
In geometry, the major axis of an ellipse is its longest diameter: a line segment that runs through the center and both foci, with ends at the two most widely separated points of the perimeter. The semi-major axis (major semiaxis) is the long ...
less than 1 AU, named after
2062 Aten.
**
Apollo asteroid
The Apollo asteroids are a group of near-Earth asteroids named after 1862 Apollo, discovered by German astronomer Karl Reinmuth in the 1930s. They are Earth-crossing asteroids that have an orbital semi-major axis greater than that of the Earth ...
s having a
semi-major axis
In geometry, the major axis of an ellipse is its longest diameter: a line segment that runs through the center and both foci, with ends at the two most widely separated points of the perimeter. The semi-major axis (major semiaxis) is the long ...
greater than 1 AU, named after
1862 Apollo.
*
Arjuna asteroid The Arjuna asteroids (also known as "Arjunas") are a dynamical group of asteroids in the Solar System. Arjunas are near-Earth objects (NEOs) whose orbits are very Earth-like in character, having low inclination, orbital periods close to one year, ...
s are somewhat vaguely defined as having orbits similar to Earth's; i.e. with an average orbital radius of around 1 AU and with low eccentricity and inclination.
Due to the vagueness of this definition some asteroids belonging to the
Atira,
Amor,
Apollo
Apollo, grc, Ἀπόλλωνος, Apóllōnos, label=genitive , ; , grc-dor, Ἀπέλλων, Apéllōn, ; grc, Ἀπείλων, Apeílōn, label=Arcadocypriot Greek, ; grc-aeo, Ἄπλουν, Áploun, la, Apollō, la, Apollinis, label= ...
or
Aten
Aten also Aton, Atonu, or Itn ( egy, jtn, ''reconstructed'' ) was the focus of Atenism, the religious system established in ancient Egypt by the Eighteenth Dynasty pharaoh Akhenaten. The Aten was the disc of the sun and originally an aspect of ...
groups can also be classified as Arjunas. The term was introduced by
Spacewatch
The Spacewatch Project is an astronomical survey that specializes in the study of minor planets, including various types of asteroids and comets at University of Arizona telescopes on Kitt Peak near Tucson, Arizona, in the United States. The Sp ...
and does not refer to an existing asteroid; examples of Arjunas include
1991 VG.
*
Earth trojan
An Earth trojan is an asteroid that orbits the Sun in the vicinity of the Earth–Sun Lagrangian points (leading 60°) or (trailing 60°), thus having an orbit similar to Earth's. Only two Earth trojans have so far been discovered. The name " ...
s are asteroids located in the Earth–Sun
Lagrangian point
In celestial mechanics, the Lagrange points (; also Lagrangian points or libration points) are points of equilibrium for small-mass objects under the influence of two massive orbiting bodies. Mathematically, this involves the solution of th ...
s and . Their location in the sky as observed from Earth's surface would be fixed at about 60 degrees east and west of the Sun, and as people tend to search for asteroids at much greater elongations few searches have been done in these locations. The only known Earth trojan is .
*
Near-Earth asteroids is a catch-all term for asteroids whose orbit closely approaches that of Earth. It includes almost all of the above groups, as well as the
Amor asteroid
The Amor asteroids are a group of near-Earth asteroids named after the archetype object 1221 Amor . The orbital perihelion of these objects is close to, but greater than, the orbital aphelion of Earth (i.e., the objects do not cross Earth's orb ...
s.
Groups out to the orbit of Mars
* The
Amor asteroids, named after
1221 Amor
1221 Amor is an asteroid and near-Earth object on an eccentric orbit, approximately in diameter. It is the namesake of the Amor asteroids, the second-largest subgroup of near-Earth objects. It was discovered by Eugène Delporte at the Uccle Obs ...
, are
near-Earth asteroids that are not
Earth-crossers, having a perihelion just outside the Earth's orbit.
*
Mars-crosser asteroid
A Mars-crossing asteroid (MCA, also Mars-crosser, MC) is an asteroid whose orbit crosses that of Mars. Some Mars-crossers numbered below 100000 are listed here. They include the two numbered Mars trojans 5261 Eureka and .
Many databases, for in ...
s have orbits that cross that of Mars, but do not necessarily closely approach the Earth's.
*
Mars trojan
The Mars trojans are a group of trojan objects that share the orbit of the planet Mars around the Sun. They can be found around the two Lagrangian points 60° ahead of and behind Mars. The origin of the Mars trojans is not well understood. One t ...
s follow or lead Mars on its orbit, at either of the two
Lagrangian point
In celestial mechanics, the Lagrange points (; also Lagrangian points or libration points) are points of equilibrium for small-mass objects under the influence of two massive orbiting bodies. Mathematically, this involves the solution of th ...
s 60° ahead () or behind (). As of November 2020, nine are known. The largest appears to be
5261 Eureka.
* Many of the Earth-, Venus-, and Mercury-crosser asteroids have aphelia greater than 1 AU.
The asteroid belt
![Kirkwood Gaps](https://upload.wikimedia.org/wikipedia/commons/d/d3/Kirkwood_Gaps.svg)
The overwhelming majority of known asteroids have orbits lying between the orbits of
Mars
Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, only being larger than Mercury (planet), Mercury. In the English language, Mars is named for the Mars (mythology), Roman god of war. Mars is a terr ...
and
Jupiter
Jupiter is the fifth planet from the Sun and the List of Solar System objects by size, largest in the Solar System. It is a gas giant with a mass more than two and a half times that of all the other planets in the Solar System combined, but ...
, roughly between 2 and 4
AU. These could not form a planet due to the gravitational influence of Jupiter. Jupiter's gravitational influence, through
orbital resonance
In celestial mechanics, orbital resonance occurs when orbiting bodies exert regular, periodic gravitational influence on each other, usually because their orbital periods are related by a ratio of small integers. Most commonly, this relationsh ...
, clears
Kirkwood gap
A Kirkwood gap is a gap or dip in the distribution of the semi-major axes (or equivalently of the orbital periods) of the orbits of main-belt asteroids. They correspond to the locations of orbital resonances with Jupiter.
For example, there ar ...
s in the asteroid belt, first recognised by
Daniel Kirkwood
Daniel Kirkwood (September 27, 1814 – June 11, 1895) was an American astronomer.
Kirkwood was born in Harford County, Maryland to John and Agnes (née Hope) Kirkwood. He graduated in mathematics from the York County Academy in York, Pennsylv ...
in 1874.
The region with the densest concentration (lying between the Kirkwood gaps at 2.06 and 3.27 AU, with
eccentricities below about 0.3, and inclinations smaller than 30°) is called the
asteroid belt
The asteroid belt is a torus-shaped region in the Solar System, located roughly between the orbits of the planets Jupiter and Mars. It contains a great many solid, irregularly shaped bodies, of many sizes, but much smaller than planets, called ...
. It can be further subdivided by the Kirkwood Gaps into the:
* Inner asteroid belt, inside of the strong Kirkwood gap at 2.50 AU due to the 3:1 Jupiter
orbital resonance
In celestial mechanics, orbital resonance occurs when orbiting bodies exert regular, periodic gravitational influence on each other, usually because their orbital periods are related by a ratio of small integers. Most commonly, this relationsh ...
. The largest member is
4 Vesta.
** It apparently also includes a group called the main-belt I asteroids which have a semi-major axis between 2.3 AU and 2.5 AU and an inclination of less than 18°.
* Middle (or intermediate) asteroid belt, between the 3:1 and 5:2 Jupiter orbital resonances, the latter at 2.82 AU. The largest member is
Ceres
Ceres most commonly refers to:
* Ceres (dwarf planet), the largest asteroid
* Ceres (mythology), the Roman goddess of agriculture
Ceres may also refer to:
Places
Brazil
* Ceres, Goiás, Brazil
* Ceres Microregion, in north-central Goiás ...
. This group is apparently split into the:
** Main-belt IIa asteroids which have a semi-major axis between 2.5 AU and 2.706 AU and an inclination less than 33°.
** Main-belt IIb asteroids which have a semi-major axis between 2.706 AU and 2.82 AU and an inclination less than 33°.
* Outer asteroid belt between the 5:2 and 2:1 Jupiter orbital resonances. The largest member is
10 Hygiea. This group is apparently split into the:
** Main-belt IIIa asteroids which have a semi-major axis between 2.82 AU and 3.03 AU, an eccentricity less than .35, and an inclination less than 30°.
** Main-belt IIIb asteroids which have a semi-major axis between 3.03 AU and 3.27 AU, an eccentricity less than .35, and an inclination less than 30°.
Other groups out to the orbit of Jupiter
There are a number of more or less distinct asteroid groups outside the asteroid belt, distinguished either by mean distance from the Sun, or particular combinations of several orbital elements:
* The
Hungaria asteroid
The Hungaria asteroids, also known as the Hungaria group, are a dynamical group of asteroids in the asteroid belt which orbit the Sun with a semi-major axis (longest radius of an ellipse) between 1.78 and 2.00 astronomical units (AU). They are t ...
s, with a mean orbital radius between 1.78 AU and 2 AU, an eccentricity less than 0.18, and inclination between 16° and 34°. Named after
434 Hungaria, these are just outside Mars's orbit, and are possibly attracted by the 9:2 Jupiter resonance or the 3:2 Mars resonance.
* The
Phocaea asteroids, with a mean orbital radius between 2.25 AU and 2.5 AU, an eccentricity greater than 0.1, and inclination between 18° and 32°. Some sources group the Phocaeas asteroids with the Hungarias, but the division between the two groups is real and caused by the 4:1 resonance with Jupiter. Named after
25 Phocaea
Phocaea (minor planet designation: 25 Phocaea) is a stony asteroid from the inner regions of the asteroid belt, approximately 75 kilometers in diameter. It is the parent body of the Phocaea family. Discovered by Jean Chacornac in 1853, it was n ...
.
* The
Alinda asteroid
The Alinda asteroids are a dynamical group of asteroids with a semi-major axis of about 2.5 AU and an orbital eccentricity approximately between 0.4 and 0.65.Earth
Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surfa ...
. Many Alinda asteroids have perihelia very close to Earth's orbit and can be difficult to observe for this reason. Alinda asteroids are ''not'' in stable orbits and eventually will collide either with Jupiter or terrestrial planets. Named after
887 Alinda.
* The
Pallas family The Pallas family (''adj. Palladian''; ) is a small asteroid family of B-type asteroids at very high inclinations in the intermediate asteroid belt.
The namesake of the family is 2 Pallas, an extremely large asteroid with a mean diameter of about 5 ...
asteroids have a mean orbital radius between 2.7 and 2.8 AU and an inclination between 30° and 38°. Named after
2 Pallas
Pallas (minor-planet designation: 2 Pallas) is the third-largest asteroid in the Solar System by volume and mass. It is the second asteroid to have been discovered, after Ceres, and is a likely remnant protoplanet. Like Ceres, it is bel ...
.
* The
Griqua asteroid A Hecuba-gap asteroid is a member of a dynamical group of resonant asteroids located in the Hecuba gap at 3.27 AU – one of the largest Kirkwood gaps in the asteroid belt, which is considered the borderline separating the outer main belt as ...
s have an orbital radius between 3.1 AU and 3.27 AU and an eccentricity greater than 0.35. These asteroids are in stable 2:1
libration
In lunar astronomy, libration is the wagging or wavering of the Moon perceived by Earth-bound observers and caused by changes in their perspective. It permits an observer to see slightly different hemispheres of the surface at different tim ...
with Jupiter, in high-inclination orbits. There are about 5 to 10 of these known so far, with
1362 Griqua and
8373 Stephengould the most prominent.
* The
Cybele asteroids
The Cybele asteroids (also known as the "Cybeles") are a dynamical group of asteroids, named after the asteroid 65 Cybele. Considered by some as the last outpost of an extended asteroid belt, the group consists of just over 2000 members an ...
have a mean orbital radius between 3.27 AU and 3.7 AU, an eccentricity less than 0.3, and an inclination less than 25°. This group appears to cluster around the 7:4 resonance with Jupiter. Named after
65 Cybele.
*
Hilda asteroids have a mean orbital radius between 3.7 AU and 4.2 AU, an eccentricity greater than 0.07, and an inclination less than 20°. These asteroids are in a 3:2 resonance with Jupiter. Named after
153 Hilda.
* The
Thule asteroid
Thule, minor planet designation: 279 Thule, is a large asteroid from the outer asteroid belt. It is classified as a D-type asteroid and is probably composed of organic-rich silicates, carbon and anhydrous silicates. Thule was the first asteroid ...
s are in a 4:3 resonance with Jupiter and the group is known to consist of
279 Thule, , and .
* The
Jupiter trojan
The Jupiter trojans, commonly called trojan asteroids or simply trojans, are a large group of asteroids that share the planet Jupiter's orbit around the Sun. Relative to Jupiter, each trojan librates around one of Jupiter's stable Lagrange poin ...
s have a mean orbital radius between 5.05 AU and 5.4 AU, and lie in elongated, curved regions around the two
Lagrangian point
In celestial mechanics, the Lagrange points (; also Lagrangian points or libration points) are points of equilibrium for small-mass objects under the influence of two massive orbiting bodies. Mathematically, this involves the solution of th ...
s 60° ahead and behind of Jupiter. The leading point, , is called the
Greek camp
This is a list of Jupiter trojans that lie in the Greek camp, an elongated curved region around the leading Lagrangian point (), 60 ° ahead of Jupiter in its orbit.
All the asteroids at Jupiter's point have names corresponding to participants ...
and the trailing point is called the
Trojan camp
This is a list of Jupiter trojans that lie in the Trojan camp, an elongated curved region around the trailing Lagrangian point, 60° behind Jupiter.
All the asteroids at the trailing point have names corresponding to participants on the Troj ...
, after the two opposing camps of the legendary
Trojan War
In Greek mythology, the Trojan War was waged against the city of Troy by the Achaeans (Greeks) after Paris of Troy took Helen from her husband Menelaus, king of Sparta. The war is one of the most important events in Greek mythology and has ...
; with one exception apiece, objects in each node are named for members of that side of the conflict.
617 Patroclus
617 Patroclus ( ) is a large binary Jupiter trojan asteroid. It is a dark D-type asteroid and a slow rotator, due to the 103-hour orbital period of its two components. It is one of five Jovian asteroids targeted by the ''Lucy'' space probe, and ...
in the Trojan camp and
624 Hektor
624 Hektor is the largest Jupiter trojan and the namesake of the Hektor family, with a highly elongated shape equivalent in volume to a sphere of approximately 225 to 250 kilometers diameter. It was discovered on 10 February 1907, by astronome ...
in the Greek camp are "misplaced" in the enemy camps.
There is a forbidden zone between the Hildas and the Trojans (roughly 4.05 AU to 4.94 AU). Aside from
279 Thule and 228 objects in mostly unstable-looking orbits, Jupiter's gravity has swept everything out of this region.
Groups beyond the orbit of Jupiter
Most of the minor planets beyond the orbit of Jupiter are believed to be composed of
ice
Ice is water frozen into a solid state, typically forming at or below temperatures of 0 degrees Celsius or Depending on the presence of impurities such as particles of soil or bubbles of air, it can appear transparent or a more or less opaq ...
s and other
volatiles
Volatiles are the group of chemical elements and chemical compounds that can be readily vaporized. In contrast with volatiles, elements and compounds that are not readily vaporized are known as refractory substances.
On planet Earth, the term ' ...
. Many are similar to
comet
A comet is an icy, small Solar System body that, when passing close to the Sun, warms and begins to release gases, a process that is called outgassing. This produces a visible atmosphere or coma, and sometimes also a tail. These phenomena ar ...
s, differing only in that the
perihelia of their orbits are too distant from the Sun to produce a significant tail.
* The
Damocloid asteroids, also known as the "Oort cloud group," are named after
5335 Damocles. They are defined to be objects that have "fallen in" from the
Oort cloud
The Oort cloud (), sometimes called the Öpik–Oort cloud, first described in 1950 by the Dutch astronomer Jan Oort, is a theoretical concept of a cloud of predominantly icy planetesimals proposed to surround the Sun at distances ranging from 2 ...
, so their aphelia are generally still out past
Uranus
Uranus is the seventh planet from the Sun. Its name is a reference to the Greek god of the sky, Uranus (mythology), Uranus (Caelus), who, according to Greek mythology, was the great-grandfather of Ares (Mars (mythology), Mars), grandfather ...
, but their perihelia are in the inner Solar System. They have high eccentricities and sometimes high inclinations, including
retrograde orbit
Retrograde motion in astronomy is, in general, orbital or rotational motion of an object in the direction opposite the rotation of its primary, that is, the central object (right figure). It may also describe other motions such as precession or ...
s. The definition of this group is somewhat fuzzy, and may overlap significantly with comets.
* The
Centaurs
A centaur ( ; grc, κένταυρος, kéntauros; ), or occasionally hippocentaur, is a creature from Greek mythology with the upper body of a human and the lower body and legs of a horse.
Centaurs are thought of in many Greek myths as being ...
have a mean orbital radius roughly between 5.4 AU and 30 AU. They are currently believed to be
trans-Neptunian object
A trans-Neptunian object (TNO), also written transneptunian object, is any minor planet in the Solar System that orbits the Sun at a greater average distance than Neptune, which has a semi-major axis of 30.1 astronomical units (au).
Typically, ...
s that "fell in" after encounters with gas giants. The first of these to be identified was
2060 Chiron
2060 Chiron is a small Solar System body in the outer Solar System, orbiting the Sun between Saturn and Uranus. Discovered in 1977 by Charles Kowal, it was the first-identified member of a new class of objects now known as centaurs—bodies orb ...
(
944 Hidalgo was discovered before, but not identified as a distinct orbital class).
Groups at or beyond the orbit of Neptune
* The
Neptune trojan
Neptune trojans are bodies that orbit the Sun near one of the stable Lagrangian points of Neptune, similar to the Trojan (astronomy), trojans of other planets. They therefore have approximately the same orbital period as Neptune and follow rough ...
s as of February 2020 consist of 29 objects. The first one to be discovered was .
*
Trans-Neptunian object
A trans-Neptunian object (TNO), also written transneptunian object, is any minor planet in the Solar System that orbits the Sun at a greater average distance than Neptune, which has a semi-major axis of 30.1 astronomical units (au).
Typically, ...
s (TNOs) are anything with a mean orbital radius greater than 30 AU. This classification includes the Kuiper-belt objects (KBOs), the scattered disc, and the Oort cloud.
**
Kuiper-belt objects extend from roughly 30 AU to 50 AU and are broken into the following subcategories:
***
Resonant objects occupy orbital resonances with Neptune, excluding the 1:1 resonance of the Neptune trojans.
****
Plutino
In astronomy, the plutinos are a dynamical group of trans-Neptunian objects that orbit in 2:3 mean-motion resonance with Neptune. This means that for every two orbits a plutino makes, Neptune orbits three times. The dwarf planet Pluto is the lar ...
s are by far the most common resonant KBOs and are in a 2:3 resonance with Neptune, just like
Pluto
Pluto (minor-planet designation: 134340 Pluto) is a dwarf planet in the Kuiper belt, a ring of trans-Neptunian object, bodies beyond the orbit of Neptune. It is the ninth-largest and tenth-most-massive known object to directly orbit the S ...
. The perihelion of such an object tends to be close to Neptune's orbit (much as happens with Pluto), but when the object comes to perihelion, Neptune alternates between being 90 degrees ahead of and 90 degrees behind of the object, so there's no chance of a collision. The MPC defines any object with a mean orbital radius between 39 AU and 40.5 AU to be a plutino.
90482 Orcus and
28978 Ixion are among the brightest known.
**** Other resonances. There are several known objects in the 1:2 resonance, dubbed ''twotinos'', with a mean orbital radius of 47.7 AU and an eccentricity of 0.37. There are several objects in the 2:5 (mean orbital radius of 55 AU), 4:7, 4:5, 3:10, 3:5, and 3:4 resonances, among others. The largest in the 2:5 resonance is , and the largest in the 3:10 resonance is
225088 Gonggong
Gonggong (formally 225088 Gonggong; provisional designation ) is a dwarf planet, a member of the scattered disc beyond Neptune. It has a highly eccentric and inclined orbit during which it ranges from from the Sun. , its distance from the Sun i ...
.
***
Classical Kuiper-belt objects, also known as cubewanos (after
15760 Albion, which had the provisional designation from its 1992 discovery to its 2018 naming), have a mean orbital radius between approximately 40.5 AU and 47 AU. Cubewanos are objects in the Kuiper belt that didn't get scattered and didn't get locked into a resonance with Neptune. The largest is .
**
Scattered disc
The scattered disc (or scattered disk) is a distant circumstellar disc in the Solar System that is sparsely populated by icy small solar system bodies, which are a subset of the broader family of trans-Neptunian objects. The scattered-disc objec ...
objects (SDOs) typically have, unlike cubewanos and resonant objects, high-inclination, high-eccentricity orbits with perihelia that are still not too far from Neptune's orbit. They are assumed to be objects that encountered Neptune and were "scattered" out of their originally more circular orbits close to the ecliptic. The most massive known dwarf planet,
Eris, belongs to this category.
***
Detached object
Detached objects are a dynamical class of minor planets in the outer reaches of the Solar System and belong to the broader family of trans-Neptunian objects (TNOs). These objects have orbits whose points of closest approach to the Sun (perihelio ...
s (extended scattered disk) with generally highly elliptical, very large orbits of up to a few hundred AU and a perihelion too far from
Neptune
Neptune is the eighth planet from the Sun and the farthest known planet in the Solar System. It is the fourth-largest planet in the Solar System by diameter, the third-most-massive planet, and the densest giant planet. It is 17 times ...
's orbit for any significant interaction to occur. A more typical member of the extended disk is .
****
Sednoid
A sednoid is a trans-Neptunian object with a perihelion well beyond the Kuiper cliff at . Only four objects are known from this population: 90377 Sedna, , 541132 Leleākūhonua (), and , but it is suspected that there are many more. All four ha ...
s have perihelia very far removed from the orbit of Neptune. This group is named after the best-known member,
90377 Sedna. As of 2020, only 3 objects in this category have been identified, but it is suspected that there are many more.
**The
Oort cloud
The Oort cloud (), sometimes called the Öpik–Oort cloud, first described in 1950 by the Dutch astronomer Jan Oort, is a theoretical concept of a cloud of predominantly icy planetesimals proposed to surround the Sun at distances ranging from 2 ...
is a hypothetical cloud of comets with a mean orbital radius between approximately 50,000 AU and 100,000 AU. No Oort-cloud objects have been detected; the existence of this classification is only inferred from indirect evidence. Some astronomers have tentatively associated
90377 Sedna with the inner Oort cloud.
See also
*
Dwarf planet
A dwarf planet is a small planetary-mass object that is in direct orbit of the Sun, smaller than any of the eight classical planets but still a world in its own right. The prototypical dwarf planet is Pluto. The interest of dwarf planets to p ...
*
*
Minor Planet Center
The Minor Planet Center (MPC) is the official body for observing and reporting on minor planets under the auspices of the International Astronomical Union (IAU). Founded in 1947, it operates at the Smithsonian Astrophysical Observatory.
Function
...
*
Mesoplanet
Mesoplanets are planetary-mass objects with sizes smaller than Mercury but larger than Ceres. The term was coined by Isaac Asimov. Assuming size is defined in relation to equatorial radius, mesoplanets should be approximately 500 km to 2,500 km ...
References
External links
Asteroid Classification I – Dynamics ''
Minor Planet Center
The Minor Planet Center (MPC) is the official body for observing and reporting on minor planets under the auspices of the International Astronomical Union (IAU). Founded in 1947, it operates at the Smithsonian Astrophysical Observatory.
Function
...
'', (archived; 18 Apr 2011)
{{DEFAULTSORT:List Of Minor-Planet Groups
Minor-planet groups