Contact binary (small Solar System body)

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Comet 67/PKuiper belt object 486958 Arrokoth
Asteroid Itokawa
Contact binaries of varying probability among the small Solar System bodies:

A contact binary is a small Solar System body such as a minor planet or a comet, 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 piles but distinct from real binary systems such as binary asteroids. The term is also used for stellar contact binaries.

An example of a what is thought to be a contact binary is the Kuiper-belt object 486958 Arrokoth.[1]


Comet Churyumov–Gerasimenko and Comet Tuttle are most likely contact binaries,[2][3] 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 probe, also appears to be a contact binary which has resulted in an elongated, bent body. Asteroid 4179 Toutatis with its elongated shape, as photographed by Chang'e-2, is a contact binary candidate as well.[4]. Among the distant minor planets, the icy Kuiper belt object Arrokoth was confirmed to be a contact binary when the New Horizons spacecraft flew past in 2019.[1]


The table contains near-Earth objects observed by radar, considered to be contact binaries.[5]

Object Dimensions (km)
Rotation period
2063 Bacchus 2.6×1.1×1.1 14.9
4450 Pan 1.0 60
4486 Mithra 1.6 67.5
4769 Castalia 0.6 4
11066 Sigurd 3.0 8.5
(179806) 2002 TD66 0.3 9.5
2007 TU24 0.3 36
8P/Tuttle 4.5
2014 HQ124 0.4 20+

See also[edit]


  1. ^ a b "Ultima Thule is first contact binary to be explored by a spacecraft". UPI. Retrieved 21 September 2019.
  2. ^ Quick Rosetta update: Churyumov-Gerasimenko is a contact binary!
  3. ^ Success! A final flawless burn. Rosetta now in tandem with its comet
  4. ^ The formation mechanism of 4179 Toutatis' elongated bi-lobed structure in a close Earth encounter scenario
  5. ^ Dr. Lance A. M. Benner (18 November 2013). "Binary and Ternary near-Earth Asteroids detected by radar". NASA/JPL Asteroid Radar Research. Retrieved 1 March 2014.