Binary asteroid

A binary asteroid is a system of two asteroids orbiting their common center of mass, in analogy with binary stars. The first such system to be discovered was 243 Ida.

Binary asteroids where both bodies are roughly the same size are sometimes called "double asteroids" or "doublet asteroids". The most famous example is the 69230 Hermes system. Another example is the 90 Antiope system. Binary asteroids with a small satellite, called a "moonlet", have been more commonly observed (see 22 Kalliope, 45 Eugenia, 87 Sylvia, 107 Camilla, 121 Hermione, 130 Elektra, 283 Emma, 379 Huenna, etc.). They are also called high-size ratio binary asteroid systems.

Paired impact craters, such as the Clearwater Lakes in Canada, are possibly the result of impact by binary asteroids.

There are various explanations for the formation of these binary asteroid systems. Recent works suggest that most of them have a significant macro-porosity (a "rubble-pile" interior). The satellite orbiting around large main-belt asteroids such as 22 Kalliope, 45 Eugenia or 87 Sylvia could formed by disruption of a parent body after impact or fission after an oblique impact. Transneptuniaon binary asteroids may have formed during the formation of the solar system by mutual capture or three body interaction. Near Earth asteroids which orbit in the inner part of our solar system may have split by tidal disruption after a close encounter with a terrestrial planet. Finally a second scenario was proposed to explain the high frequency of binary in the NEA and inner-part of the mainbelt. This model, described in the journal Nature (June 10, 2008), shows that when solar energy spins a “rubble pile” asteroid to a sufficiently fast rate, material is slung off from around the asteroid’s equator. This process also exposes fresh material at the poles of the asteroid.

See also

• asteroid moon
• List of asteroid moons
• Yarkovsky-O'Keefe-Radzievskii-Paddack effect (YORP effect)