Cubewano
Encyclopedia
A classical Kuiper belt object, also called a cubewano (icon "QB1-o")
is a low-eccentricity Kuiper belt
Kuiper belt
The Kuiper belt , sometimes called the Edgeworth–Kuiper belt, is a region of the Solar System beyond the planets extending from the orbit of Neptune to approximately 50 AU from the Sun. It is similar to the asteroid belt, although it is far larger—20 times as wide and 20 to 200 times as massive...
object (KBO) that orbit
Orbit
In physics, an orbit is the gravitationally curved path of an object around a point in space, for example the orbit of a planet around the center of a star system, such as the Solar System...
s beyond 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...
and is not controlled by an orbital resonance with Neptune
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...
. Cubewanos have 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...
in the 40–50 AU
Astronomical unit
An astronomical unit is a unit of length equal to about or approximately the mean Earth–Sun distance....
range and, unlike 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...
, do not cross Neptune’s orbit. That is, they have low-eccentricity and sometimes low-inclination orbits like the classical planets.
The name "cubewano" derives from the first 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...
(TNO) found after Pluto and Charon
Charon (moon)
Charon is the largest satellite of the dwarf planet Pluto. It was discovered in 1978 at the United States Naval Observatory Flagstaff Station. Following the 2005 discovery of two other natural satellites of Pluto , Charon may also be referred to as Pluto I...
, . 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:
- Makemake, the largest known cubewano and a dwarf planet
- (50000) Quaoar and (20000) Varuna, each considered the largest TNO at the time of discovery
- 19521 Chaos19521 Chaos19521 Chaos , is a cubewano, a Kuiper-belt object not in resonance with any planet. It is a likely dwarf planet. Chaos was discovered in 1998 by the Deep Ecliptic Survey, with Kitt Peak's 4 m telescope. Assuming it has an albedo of 0.09, the absolute magnitude of 4.9 would make it about...
, 58534 Logos58534 Logos58534 Logos is a small Kuiper-belt object, more specifically a cubewano, notable for having a comparatively large satellite named Zoe. For a small, about 80 km in diameter, KBO it has a very high albedo...
, 53311 Deucalion53311 Deucalion53311 Deucalion is a trans-Neptunian object . It was discovered in 1999 by the Deep Ecliptic Survey . It is classified as a cubewano, and named after Deucalion, from Greek mythology.-References:...
, 66652 Borasisi66652 Borasisi66652 Borasisi , provisionally known as , is a trans-Neptunian object discovered in 1999 by A. Trujillo, J. Luu and D. Jewitt and identified as binary in 2003 by K...
, 88611 Teharonhiawako88611 Teharonhiawako88611 Teharonhiawako is a trans-Neptunian object and a member of the Kuiper belt, measuring 156–196 km in diameter. It is a binary object, with a large companion named Sawiskera Teharonhiawako I Sawiskera), which at 108–136 km in diameter is about two-thirds the size of its ...
, , ,
Haumea (2003 EL61) was provisionally listed as a cubewano by the Minor Planet Center
Minor Planet Center
The Minor Planet Center operates at the Smithsonian Astrophysical Observatory , which is part of the Center for Astrophysics along with the Harvard College Observatory ....
in 2006, but turned out to be resonant.
Orbits: 'hot' and 'cold' populations
Most cubewanos are found between the 2:3 orbital resonanceOrbital 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 (populated by plutino
Plutino
In astronomy, a plutino is a trans-Neptunian object in 2:3 mean motion resonance with Neptune. For every 2 orbits that a plutino makes, Neptune orbits 3 times. Plutinos are named after Pluto, which follows an orbit trapped in the same resonance, with the Italian diminutive suffix -ino...
s) and the 1:2 resonance. 50000 Quaoar
50000 Quaoar
50000 Quaoar is a rocky trans-Neptunian object in the Kuiper belt with one known moon. Discovered on June 4, 2002 by astronomers Chad Trujillo and Michael Brown at the California Institute of Technology from images acquired at the Samuel Oschin Telescope at Palomar Observatory, it is thought by...
, for example, has a near-circular orbit close to the ecliptic
Ecliptic
The ecliptic is the plane of the earth's orbit around the sun. In more accurate terms, it is the intersection of the celestial sphere with the ecliptic plane, which is the geometric plane containing the mean orbit of the Earth around the Sun...
. Plutinos, on the other hand, have more eccentric orbits bringing some of them closer to the Sun than 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...
.
The majority of objects (the so-called 'cold population'), have low inclinations and near-circular orbits. A smaller population (the 'hot population') is characterised by highly inclined, more eccentric orbits.
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....
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 '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 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 while confirming 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
Binary asteroid
A binary asteroid is a system of two asteroids orbiting their common center of mass, in analogy with binary stars. 243 Ida was the first binary asteroid to be identified when the Galileo spacecraft did a flyby in 1993...
. 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 objectResonant 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). The Minor Planet Center
Minor Planet Center
The Minor Planet Center operates at the Smithsonian Astrophysical Observatory , which is part of the Center for Astrophysics along with the Harvard College Observatory ....
(MPC) and 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....
(DES) do not list cubewanos (classical objects) using the same exact criteria. Many TNOs classified as cubewanos by the MPC are classified as ScatNear (possibly scattered
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....
by Neptune) by the DES. Dwarf planet Makemake is such a borderline classical cubewano/scatnear object. may be an inner cubewano near the plutino
Plutino
In astronomy, a plutino is a trans-Neptunian object in 2:3 mean motion resonance with Neptune. For every 2 orbits that a plutino makes, Neptune orbits 3 times. Plutinos are named after Pluto, which follows an orbit trapped in the same resonance, with the Italian diminutive suffix -ino...
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 remains blurred. As of 2010, there are 377 objects with perihelion (q) > 40 AU and aphelion (Q) < 47AU.
DES classification
Introduced by the report from the Deep Ecliptic SurveyDeep 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....
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 resonantResonant trans-Neptunian objectIn 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...
- it has the average Tisserand's parameterTisserand's parameterTisserand's parameter is a combination of orbital elements used in a restricted three-body problem.-Definition:...
exceeding 3 - its average eccentricity is less than 0.2.
SSBN07 classification
An alternative classification, introduced by B. GladmanBrett J. Gladman
Brett J. Gladman is a Canadian astronomer and a full professor at the University of British Columbia's Department of Physics and Astronomy in Vancouver, British Columbia. He holds the Canada Research Chair in Planetary Astronomy.-Career:...
, B. Marsden
Brian G. Marsden
Brian Geoffrey Marsden was a British astronomer born in Cambridge, England, and educated at The Perse School in Cambridge, New College, Oxford and Yale University. Dr...
and C. VanLaerhoven in 2007, uses 10 million years orbit integration instead of the Tisserand parameter. Classical objects are defined as not resonant and not being currently scattered by Neptune.
Formally, this definition includes as classical all objects with the current orbits that
- are non-resonant (see the definition of the method)
- have the semi-major axis greater than that of Neptune (i.e. excluding Centaurs) but less than 2000 AU (to exclude Inner Oort Cloud Objects)
- have the 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) – named Inner classical belt, or more than 48.7 (1:2 resonance) – named Outer classical belt while reserving the term Main classical belt for the orbits between these two resonances.
Families
The first collisional familyCollisional family
In astronomy, a collisional family is a group of objects that are thought to have a common origin in an impact . They have similar compositions, and most share similar orbital elements....
—a group of objects thought to be remnants from the breakup of a single body—is the Haumea family
Haumea family
The Haumea family is the only identified trans-Neptunian collisional family; that is, the only group of trans-Neptunian objects with similar orbital parameters and spectra that suggest they originated in the disruptive impact of a progenitor body...
. 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 (H2O) and no or very little tholin
Tholin
Tholin [after the ancient Greek word meaning "not clear"] is a heteropolymer molecule formed by solar ultraviolet irradiation of simple organic compounds such as methane or ethane. Tholins do not form naturally on modern-day Earth, but are found in great abundance on the surface of icy bodies in...
s. The surface composition is inferred from their neutral (as opposed to red) colour and deep absorption at 1.5 and 2. μm
Micrometre
A micrometer , is by definition 1×10-6 of a meter .In plain English, it means one-millionth of a meter . Its unit symbol in the International System of Units is μm...
in infrared
Infrared
Infrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...
spectrum
Electromagnetic spectrum
The electromagnetic spectrum is the range of all possible frequencies of electromagnetic radiation. The "electromagnetic spectrum" of an object is the characteristic distribution of electromagnetic radiation emitted or absorbed by that particular object....
.
†As of 2008. The four brightest objects of the family are situated on the graphs inside the circle representing Haumea.
External links
- David Jewitt's Kuiper belt site
- The Kuiper Belt Electronic Newsletter
- Minor Planet Center List of Trans-Neptunian objects
- TNO pages at johnstonarchive
- Plot of the current positions of bodies in the Outer Solar System