A contact binary is a
small Solar System body
A small Solar System body (SSSB) is an object in the Solar System that is neither a planet, a dwarf planet, nor a natural satellite. The term was first defined in 2006 by the International Astronomical Union (IAU) as follows: "All other obje ...
such as a
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 ''mino ...
or a
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 are ...
that is composed of two bodies that have
gravitated toward each other until they touch, resulting in a
bilobated, peanut-like overall shape. Contact binaries are often
rubble pile
In astronomy, a rubble pile is a celestial body that is not a monolith, consisting instead of numerous pieces of rock that have coalesced under the influence of gravity. Rubble piles have low density because there are large cavities between the ...
s but distinct from real
binary system
A binary system is a system of two astronomical bodies which are close enough that their gravitational attraction causes them to orbit each other around a barycenter ''(also see animated examples)''. More restrictive definitions require that thi ...
s such as
binary asteroid
A binary asteroid is a system of two asteroids orbiting their common barycenter. The binary nature of 243 Ida was discovered when the Galileo spacecraft flew by the asteroid in 1993. Since then numerous binary asteroids and several triple ast ...
s. The term is also used for
stellar contact binaries.
An example of what is thought to be a contact binary is the
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 ti ...
object
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 ...
, which was imaged by the ''
New Horizons'' spacecraft during its flyby in January 2019.
Description
Comet Churyumov–Gerasimenko and
Comet Tuttle are most likely contact binaries,
while
asteroid
An asteroid is a minor planet of the inner Solar System. Sizes and shapes of asteroids vary significantly, ranging from 1-meter rocks to a dwarf planet almost 1000 km in diameter; they are rocky, metallic or icy bodies with no atmosphere.
...
s suspected of being contact binaries include the unusually elongated
624 Hektor and the bilobated
216 Kleopatra and
4769 Castalia
4769 Castalia (; '' prov. designation:'' ) is a near-Earth object and potentially hazardous asteroid of the Apollo group, approximately in diameter and was the first asteroid to be modeled by radar imaging. It was discovered on 9 August 1989, by ...
.
25143 Itokawa
25143 Itokawa (provisional designation ) is a sub-kilometer near-Earth object of the Apollo group and a potentially hazardous asteroid. It was discovered by the LINEAR program in 1998 and later named after Japanese rocket engineer Hideo Itokawa. ...
, which was photographed by the ''
Hayabusa'' probe, also appears to be a contact binary which has resulted in an elongated, bent body. Asteroid
4179 Toutatis
4179 Toutatis, provisional designation , is an elongated, stony asteroid and slow rotator, classified as a near-Earth object and potentially hazardous asteroid
A potentially hazardous object (PHO) is a near-Earth object – either an asteroi ...
with its elongated shape, as photographed by ''
Chang'e-2
Chang'e 2 (; ) is a Chinese unmanned lunar probe that was launched on 1 October 2010. It was a follow-up to the Chang'e 1 lunar probe, which was launched in 2007. Chang'e 2 was part of the first phase of the Chinese Lunar Exploration Program, an ...
'', is a contact binary candidate as well.
Among the
distant minor planets
A distant minor planet, or ''distant object'', is any minor planet found beyond Jupiter in the outer Solar System that is not commonly thought of as an "asteroid". The umbrella term is used by IAU's Minor Planet Center (MPC), which is responsible ...
, the icy Kuiper belt object Arrokoth was confirmed to be a contact binary when the ''
New Horizons
''New Horizons'' is an 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 Institute (SwRI), with a ...
'' spacecraft
flew past in 2019.
Candidates
The table contains
near-Earth object
A near-Earth object (NEO) is any small Solar System body whose orbit brings it into proximity with Earth. By convention, a Solar System body is a NEO if its closest approach to the Sun (perihelion) is less than 1.3 astronomical units (AU) ...
s observed by
radar, considered to be contact binaries (candidate objects with a darker background).
LCDB = Lightcurve Database.
See also
*
Binary system (astronomy)
A binary system is a system of two astronomical bodies which are close enough that their gravitational attraction causes them to orbit each other around a barycenter ''(also see animated examples)''. More restrictive definitions require that thi ...
References
{{DEFAULTSORT:Contact Binary (Asteroid)
Bodies of the Solar System