![Cubewanos](https://upload.wikimedia.org/wikipedia/commons/5/5b/Cubewanos.png)
A classical Kuiper belt object, also called a cubewano ( "QB1-o"), is a low-eccentricity
Kuiper belt
The Kuiper belt () is a circumstellar disc in the outer Solar System, extending from the orbit of Neptune at 30 astronomical units (AU) to approximately 50 AU from the Sun. It is similar to the asteroid belt, but is far larger—20 times ...
object (KBO) that
orbit
In celestial mechanics, an orbit is the curved trajectory of an object such as the trajectory of a planet around a star, or of a natural satellite around a planet, or of an artificial satellite around an object or position in space such as a p ...
s beyond
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 ...
and is not controlled by an
orbital resonance with Neptune. Cubewanos have orbits with
semi-major axes in the 40–50
AU range and, unlike
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 ...
, do not cross Neptune's orbit. That is, they have low-
eccentricity
Eccentricity or eccentric may refer to:
* Eccentricity (behavior), odd behavior on the part of a person, as opposed to being "normal"
Mathematics, science and technology Mathematics
* Off-center, in geometry
* Eccentricity (graph theory) of a v ...
and sometimes low-
inclination
Orbital inclination measures the tilt of an object's orbit around a celestial body. It is expressed as the angle between a Plane of reference, reference plane and the orbital plane or Axis of rotation, axis of direction of the orbiting object ...
orbits like the classical planets.
The name "cubewano" derives from the first
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, ...
(TNO) found after Pluto and
Charon
In Greek mythology, Charon or Kharon (; grc, Χάρων) is a psychopomp, the ferryman of Hades, the Greek underworld. He carries the souls of those who have been given funeral rites across the rivers Acheron and Styx, which separate the wo ...
:
15760 Albion
15760 Albion, provisional designation , was the first trans-Neptunian object to be discovered after Pluto and Charon. Measuring about 108–167 kilometres in diameter, it was discovered in 1992 by David C. Jewitt and Jane X. Luu at the Mauna Kea ...
, which until January 2018 had only the provisional designation (15760) 1992 QB1. Similar objects found later were often called "QB1-o's", or "cubewanos", after this object, though the term "classical" is much more frequently used in the scientific literature.
Objects identified as cubewanos include:
*
15760 Albion
15760 Albion, provisional designation , was the first trans-Neptunian object to be discovered after Pluto and Charon. Measuring about 108–167 kilometres in diameter, it was discovered in 1992 by David C. Jewitt and Jane X. Luu at the Mauna Kea ...
(aka 1992 QB1 and gave rise to term 'Cubewano')
*
136472 Makemake, the largest known cubewano and a
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 ...
*
50000 Quaoar
Quaoar (50000 Quaoar), provisional designation , is a dwarf planet in the Kuiper belt, a region of icy planetesimals beyond Neptune. A non-resonant object (cubewano), it measures approximately in diameter, about half the diameter of Pluto. The ...
and
20000 Varuna
20000 Varuna, provisional designation , is a large trans-Neptunian object in the Kuiper belt. It was discovered in November 2000 by American astronomer Robert McMillan during a Spacewatch survey at the Kitt Peak National Observatory. It is na ...
, each considered the largest TNO at the time of discovery
*
19521 Chaos
19521 Chaos is a cubewano, a Kuiper-belt object not in resonance with any planet. Chaos was discovered in 1998 by the Deep Ecliptic Survey with Kitt Peak's 4 m telescope. Its albedo is , making it, with its absolute magnitude (H) of 4.8, ...
,
58534 Logos,
53311 Deucalion
53311 Deucalion , provisional designation , is a trans-Neptunian object from the classical Kuiper belt, with a diameter of approximately , located in the outermost region of the Solar System. The cubewano belongs to the cold population and was di ...
,
66652 Borasisi
66652 Borasisi, or as a binary (66652) Borasisi-Pabu, is a binary classical Kuiper belt object. It was discovered in September 1999 by Chad Trujillo, Jane X. Luu and David C. Jewitt and identified as a binary in 2003 by K. Noll and colleagues us ...
,
88611 Teharonhiawako
88611 Teharonhiawako, or (88611) Teharonhiawako–Sawiskera as a binary, is a trans-Neptunian object and a member of the cold classical Kuiper belt, measuring about 220 km in diameter. It is a binary object, with a large companion named ...
* , , ,
*
486958 Arrokoth
Arrokoth (minor-planet designation 486958 Arrokoth; provisional designation ), formerly nicknamed Ultima Thule, is a trans-Neptunian object located in the Kuiper belt. Arrokoth became the farthest and most primitive object in the Solar System ...
136108 Haumea was provisionally listed as a cubewano by the
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
...
in 2006,
but was later found to be in a
resonant
Resonance describes the phenomenon of increased amplitude that occurs when the frequency of an applied periodic force (or a Fourier component of it) is equal or close to a natural frequency of the system on which it acts. When an oscillatin ...
orbit.
[
]
: 'hot' and 'cold' populations
![TheKuiperBelt 55AU Classical](https://upload.wikimedia.org/wikipedia/commons/0/0f/TheKuiperBelt_55AU_Classical.svg)
There are two basic dynamical classes of classical Kuiper-belt bodies: those with relatively unperturbed ('cold') orbits, and those with markedly perturbed ('hot') orbits.
Most cubewanos are found between the 2:3
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 ...
with Neptune (populated by
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) and the 1:2 resonance.
50000 Quaoar
Quaoar (50000 Quaoar), provisional designation , is a dwarf planet in the Kuiper belt, a region of icy planetesimals beyond Neptune. A non-resonant object (cubewano), it measures approximately in diameter, about half the diameter of Pluto. The ...
, for example, has a near-circular orbit close to the
ecliptic
The ecliptic or ecliptic plane is the orbital plane of the Earth around the Sun. From the perspective of an observer on Earth, the Sun's movement around the celestial sphere over the course of a year traces out a path along the ecliptic again ...
. Plutinos, on the other hand, have more eccentric orbits bringing some of them closer to the Sun than
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 ...
.
The majority of classical objects, the so-called ''cold population'', have low inclinations (< 5
°) and near-circular orbits, lying between 42 and 47 AU. A smaller population (the ''hot population'') is characterised by highly inclined, more eccentric orbits.
[)] The terms 'hot' and 'cold' has nothing to do with surface or internal temperatures, but rather refer to the orbits of the objects, by analogy to molecules in a gas, which increase their relative velocity as they heat up.
The
Deep Ecliptic Survey
The Deep Ecliptic Survey (DES) is a project to find Kuiper belt objects (KBOs), using the facilities of the National Optical Astronomy Observatory (NOAO). The principal investigator is Robert L. Millis.
Since 1998 through the end of 2003, the sur ...
reports the distributions of the two populations; one with the inclination centered at 4.6° (named ''Core'') and another with inclinations extending beyond 30° (''Halo'').
[
()]
Distribution
The vast majority of KBOs (more than two-thirds) have inclinations of less than 5° and eccentricities of less than 0.1 . Their semi-major axes show a preference for the middle of the main belt; arguably, smaller objects close to the limiting resonances have been either captured into resonance or have their orbits modified by Neptune.
The 'hot' and 'cold' populations are strikingly different: more than 30% of all cubewanos are in low inclination, near-circular orbits. The parameters of the plutinos’ orbits are more evenly distributed, with a local maximum in moderate eccentricities in 0.15–0.2 range, and low inclinations 5–10°.
See also the comparison with
scattered disk objects.
When the orbital eccentricities of cubewanos and plutinos are compared, it can be seen that the cubewanos form a clear 'belt' outside Neptune's orbit, whereas the plutinos approach, or even cross Neptune's orbit. When orbital inclinations are compared, 'hot' cubewanos can be easily distinguished by their higher inclinations, as the plutinos typically keep orbits below 20°. (No clear explanation currently exists for the inclinations of 'hot' cubewanos.)
Cold and hot populations: physical characteristics
In addition to the distinct orbital characteristics, the two populations display different physical characteristics.
The difference in colour between the red cold population, such as
486958 Arrokoth
Arrokoth (minor-planet designation 486958 Arrokoth; provisional designation ), formerly nicknamed Ultima Thule, is a trans-Neptunian object located in the Kuiper belt. Arrokoth became the farthest and most primitive object in the Solar System ...
, and more heterogeneous hot population was observed as early as in 2002.
[
]
Recent studies, based on a larger data set, indicate the cut-off inclination of 12° (instead of 5°) between the cold and hot populations and confirm the distinction between the homogenous red cold population and the bluish hot population.
[
]
Another difference between the low-inclination (cold) and high-inclination (hot) classical objects is the observed number of
binary objects. Binaries are quite common on low-inclination orbits and are typically similar-brightness systems. Binaries are less common on high-inclination orbits and their components typically differ in brightness. This correlation, together with the differences in colour, support further the suggestion that the currently observed classical objects belong to at least two different overlapping populations, with different physical properties and orbital history.
[
]
Toward a formal definition
There is no official definition of 'cubewano' or 'classical KBO'. However, the terms are normally used to refer to objects free from significant perturbation from Neptune, thereby excluding KBOs in orbital resonance with Neptune (
resonant trans-Neptunian object
In astronomy, a resonant trans-Neptunian object is a trans-Neptunian object (TNO) 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 ...
s). The
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
...
(MPC) and the
Deep Ecliptic Survey
The Deep Ecliptic Survey (DES) is a project to find Kuiper belt objects (KBOs), using the facilities of the National Optical Astronomy Observatory (NOAO). The principal investigator is Robert L. Millis.
Since 1998 through the end of 2003, the sur ...
(DES) do not list cubewanos (classical objects) using the same criteria. Many TNOs classified as cubewanos by the MPC are classified as ScatNear (possibly
scattered
Scattered may refer to:
Music
* ''Scattered'' (album), a 2010 album by The Handsome Family
* "Scattered" (The Kinks song), 1993
* "Scattered", a song by Ace Young
* "Scattered", a song by Lauren Jauregui
* "Scattered", a song by Green Day from ' ...
by Neptune) by the DES. Dwarf planet
Makemake
Makemake (minor-planet designation 136472 Makemake) is a dwarf planet and – depending on how they are defined – the second-largest Kuiper belt object in the classical population, with a diameter approximately 60% that of Pluto. It ...
is such a borderline classical cubewano/scatnear object. may be an inner cubewano near the
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. Furthermore, there is evidence that the Kuiper belt has an 'edge', in that an apparent lack of low-inclination objects beyond 47–49 AU was suspected as early as 1998 and shown with more data in 2001.
[
] Consequently, the traditional usage of the terms is based on the orbit's semi-major axis, and includes objects situated between the 2:3 and 1:2 resonances, that is between 39.4 and 47.8 AU (with exclusion of these resonances and the minor ones in-between).
These definitions lack precision: in particular the boundary between the classical objects and the
scattered disk
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 ...
remains blurred. , there are 634 objects with perihelion (q) > 40 AU and aphelion (Q) < 47 AU.
DES classification
Introduced by the report from the
Deep Ecliptic Survey
The Deep Ecliptic Survey (DES) is a project to find Kuiper belt objects (KBOs), using the facilities of the National Optical Astronomy Observatory (NOAO). The principal investigator is Robert L. Millis.
Since 1998 through the end of 2003, the sur ...
by J. L. Elliott et al. in 2005 uses formal criteria based on the mean orbital parameters.
Put informally, the definition includes the objects that have never crossed the orbit of Neptune. According to this definition, an object qualifies as a classical KBO if:
* it is not
resonant
Resonance describes the phenomenon of increased amplitude that occurs when the frequency of an applied periodic force (or a Fourier component of it) is equal or close to a natural frequency of the system on which it acts. When an oscillatin ...
* its average
Tisserand's parameter
Tisserand's parameter (or Tisserand's invariant) is a value calculated from several orbital elements (semi-major axis, orbital eccentricity and inclination) of a relatively small object and a larger " perturbing body". It is used to distinguish dif ...
with respect to Neptune exceeds 3
* its average eccentricity is less than 0.2.
SSBN07 classification
An alternative classification, introduced by
B. Gladman,
B. Marsden and C. van Laerhoven in 2007, uses a 10-million-year orbit integration instead of the Tisserand's parameter. Classical objects are defined as not resonant and not being currently scattered by Neptune.
[
]
Formally, this definition includes as ''classical'' all objects with their ''current'' orbits that
*are non-resonant (see the
definition of the method)
*have a semi-major axis greater than that of Neptune (30.1 AU; i.e. excluding centaurs) but less than 2000 AU (to exclude inner-Oort-cloud objects)
*are not being scattered by Neptune
*have their eccentricity
(to exclude detached objects)
Unlike other schemes, this definition includes the objects with major semi-axis less than 39.4 AU (2:3 resonance)—termed ''inner classical belt'', or more than 48.7 (1:2 resonance) – termed ''outer classical belt'', and reserves the term ''main classical belt'' for the orbits between these two resonances.
Families
The first known
collisional family
In astronomy, a collisional family is a group of objects that are thought to have a common origin in an impact (collision). They have similar compositions and most share similar orbital elements.
Numerous asteroid families, most of the irregular ...
in the classical Kuiper belt—a group of objects thought to be remnants from the breakup of a single body—is the
Haumea family
The Haumea or Haumean family is the only identified trans-Neptunian collisional family; that is, the only group of trans-Neptunian objects (TNOs) with similar orbital parameters and spectra (nearly pure water-ice) that suggest they originated in ...
.
[
] It includes Haumea, its moons, and seven smaller bodies.
† The objects not only follow similar orbits but also share similar physical characteristics. Unlike many other KBO their surface contains large amounts of ice (H
2O) and no or very little
tholin
Tholins (after the Greek (') "hazy" or "muddy"; from the ancient Greek word meaning "sepia ink") are a wide variety of organic compounds formed by solar ultraviolet or cosmic ray irradiation of simple carbon-containing compounds such as carbon ...
s.
[
] The surface composition is inferred from their neutral (as opposed to red) colour and deep absorption at 1.5 and 2.
μm
The micrometre ( international spelling as used by the International Bureau of Weights and Measures; SI symbol: μm) or micrometer (American spelling), also commonly known as a micron, is a unit of length in the International System of Unit ...
in
infrared
Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from around ...
spectrum
A spectrum (plural ''spectra'' or ''spectrums'') is a condition that is not limited to a specific set of values but can vary, without gaps, across a continuum. The word was first used scientifically in optics to describe the rainbow of colors i ...
.
[
] Several other collisional families might reside in the classical Kuiper belt.
†As of 2008. The four brightest objects of the family are situated on the graphs ''inside'' the circle representing Haumea.
Exploration
![2014 MU69 orbit](https://upload.wikimedia.org/wikipedia/commons/5/53/2014_MU69_orbit.jpg)
As of January 2019, only one classical Kuiper belt object has been observed up close by spacecraft. Both
Voyager spacecraft
The Voyager program is an American scientific program that employs two robotic interstellar probes, ''Voyager 1'' and ''Voyager 2''. They were launched in 1977 to take advantage of a favorable alignment of Jupiter and Saturn, to fly near the ...
have passed through the region before the discovery of the Kuiper belt.
New Horizons
''New Horizons'' is an Interplanetary spaceflight, interplanetary space probe that was launched as a part of NASA's New Frontiers program. Engineered by the Johns Hopkins University Applied Physics Laboratory (APL) and the Southwest Research ...
was the first mission to visit a classical KBO. After its successful exploration of the
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 ...
system in 2015, the
NASA
The National Aeronautics and Space Administration (NASA ) is an independent agency of the US federal government responsible for the civil space program, aeronautics research, and space research.
NASA was established in 1958, succeeding t ...
spacecraft has visited the small KBO 486958 Arrokoth at a distance of on 1 January 2019.
List
Here is a very generic list of classical Kuiper belt objects. , there are about 779 objects with and .
*
15760 Albion
15760 Albion, provisional designation , was the first trans-Neptunian object to be discovered after Pluto and Charon. Measuring about 108–167 kilometres in diameter, it was discovered in 1992 by David C. Jewitt and Jane X. Luu at the Mauna Kea ...
*
20000 Varuna
20000 Varuna, provisional designation , is a large trans-Neptunian object in the Kuiper belt. It was discovered in November 2000 by American astronomer Robert McMillan during a Spacewatch survey at the Kitt Peak National Observatory. It is na ...
*
*
*
*
*
*
*
120347 Salacia
120347 Salacia, provisional designation , is a large planetoid in the Kuiper belt, approximately 850 kilometers in diameter. As of 2018, it is located 44.8 astronomical units from the Sun, and reaches apparent magnitude 20.7 at opposition.
Salac ...
*
*
*
*
148780 Altjira
*
*
*
174567 Varda
174567 Varda (provisional designation ) is a binary trans-Neptunian planetoid of the resonant hot classical population of the Kuiper belt, located in the outermost region of the Solar System. Its moon, Ilmarë, was discovered in 2009.
Michael ...
*
*
19521 Chaos
19521 Chaos is a cubewano, a Kuiper-belt object not in resonance with any planet. Chaos was discovered in 1998 by the Deep Ecliptic Survey with Kitt Peak's 4 m telescope. Its albedo is , making it, with its absolute magnitude (H) of 4.8, ...
*
*
*
*
*
*
486958 Arrokoth
Arrokoth (minor-planet designation 486958 Arrokoth; provisional designation ), formerly nicknamed Ultima Thule, is a trans-Neptunian object located in the Kuiper belt. Arrokoth became the farthest and most primitive object in the Solar System ...
*
50000 Quaoar
Quaoar (50000 Quaoar), provisional designation , is a dwarf planet in the Kuiper belt, a region of icy planetesimals beyond Neptune. A non-resonant object (cubewano), it measures approximately in diameter, about half the diameter of Pluto. The ...
*
*
53311 Deucalion
53311 Deucalion , provisional designation , is a trans-Neptunian object from the classical Kuiper belt, with a diameter of approximately , located in the outermost region of the Solar System. The cubewano belongs to the cold population and was di ...
*
*
*
*
58534 Logos
*
66652 Borasisi
66652 Borasisi, or as a binary (66652) Borasisi-Pabu, is a binary classical Kuiper belt object. It was discovered in September 1999 by Chad Trujillo, Jane X. Luu and David C. Jewitt and identified as a binary in 2003 by K. Noll and colleagues us ...
*
*
79360 Sila–Nunam
79360 Sila–Nunam, provisional designation , is a cold classical Kuiper belt object (cubewano) and binary asteroid, binary system made up of components of almost equal size, called Sila and Nunam, orbiting beyond Neptune in the Solar System. The ...
*
*
*
*
*
88611 Teharonhiawako
88611 Teharonhiawako, or (88611) Teharonhiawako–Sawiskera as a binary, is a trans-Neptunian object and a member of the cold classical Kuiper belt, measuring about 220 km in diameter. It is a binary object, with a large companion named ...
*
See also
*
Lists of astronomical objects
This is a list of lists, grouped by type of astronomical object.
Solar System
* List of Solar System objects
* List of gravitationally rounded objects of the Solar System
* List of Solar System objects most distant from the Sun
* List of So ...
Footnotes
References
External links
*
*
*
*
*
{{DEFAULTSORT:Classical Kuiper belt object