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 objects, ...
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 ...
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 th ...
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 a ...
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 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
asteroids suspected of being contact binaries include the unusually elongated
624 Hektor and the bilobated
216 Kleopatra and
4769 Castalia.
25143 Itokawa, which was photographed by the ''
Hayabusa
was a robotic spacecraft developed by the Japan Aerospace Exploration Agency (JAXA) to return a sample of material from a small near-Earth asteroid named 25143 Itokawa to Earth for further analysis.
''Hayabusa'', formerly known as MUSES-C fo ...
'' 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 of the Apollo asteroid and Alinda asteroid groups, approximately 2.5 kilometers in ...
with its elongated shape, as photographed by ''
Chang'e-2'', 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 responsibl ...
, the icy Kuiper belt object Arrokoth was confirmed to be a contact binary when the ''
New Horizons'' 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
Radar is a detection system that uses radio waves to determine the distance ('' ranging''), angle, and radial velocity of objects relative to the site. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, we ...
, considered to be contact binaries (candidate objects with a darker background).
LCDB = Lightcurve Database.
See also
*
Binary system (astronomy)
References
{{DEFAULTSORT:Contact Binary (Asteroid)
Bodies of the Solar System