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Contact binary (small Solar System body)

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.

Comet 67/PKuiper belt object 2014 MU69
Asteroid Itokawa
Possible contact binaries among the small Solar System bodies:



Comet Churyumov–Gerasimenko and Comet Tuttle are most likely contact binaries,[1][2] 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.[3]. Among the distant minor planets, the icy Kuiper belt object 2014 MU69 was confirmed to be a contact binary when the New Horizons spacecraft flew past in 2019.

While there is not sufficient observational data, it is thought that these kind of small body conglomerates are abundant. For example, about 10–15% of the near-Earth population larger than 200 meters are expected to be contact binaries with two lobes.[4]


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 alsoEdit


  1. ^ Quick Rosetta update: Churyumov-Gerasimenko is a contact binary!
  2. ^ Success! A final flawless burn. Rosetta now in tandem with its comet
  3. ^ The formation mechanism of 4179 Toutatis' elongated bi-lobed structure in a close Earth encounter scenario
  4. ^ Michael Busch (12 March 2012). "Near-Earth Asteroids and Radar Speckle Tracking" (PDF) (PDF). Retrieved 22 February 2019.
  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.