Abinary asteroid is a system of twoasteroids orbiting their commonbarycenter. The binary nature of243 Ida was discovered when theGalileo spacecraft flew by the asteroid in 1993. Since thennumerous binary asteroids andseveral triple asteroids have been detected.[1]
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The mass ratio of the two components – called the "primary" and "secondary" of a binary system – is an important characteristic. Most binary asteroids have a large mass ratio, i.e. a relatively small satellite in orbit around the main component. Systems with one or more smallmoons – also called "companions" or simply "satellites" – include87 Sylvia,107 Camilla and45 Eugenia (all triples),121 Hermione,130 Elektra (a quadruple),22 Kalliope,283 Emma,379 Huenna,243 Ida and4337 Arecibo (in order of decreasing primary size). Some binary systems have a mass ratio near unity, i.e., two components of similar mass. They include90 Antiope,2006 VW139,2017 YE5 and69230 Hermes, with average component diameters of 86, 1.8, 0.9 and 0.8 km, respectively.
In August 2024Gaia reported 352 new binary asteroid candidates.[2][3]
Several theories have been posited to explain the formation of binary-asteroid systems. Many systems have significant macro-porosity (a "rubble-pile" interior). The satellites orbiting largemain-belt asteroids such as 22 Kalliope, 45 Eugenia or 87 Sylvia may have formed by disruption of a parent body after impact or fission after an oblique impact.Trans-Neptunian binaries 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 the Solar System, most likely form by spin-up and mass shedding,[4] likely as a result of theYORP effect. Numerical simulations suggest that when solar energy spins a “rubble pile” asteroid to a sufficiently fast rate by the YORP effect, material is thrown from the asteroid's equator.[5] This process also exposes fresh material at the poles of the asteroid.[5][6]
![Time-lapse video of binary main-belt comet 2006 VW139 (288P)[7]](/mt/?noimg=&dark=on&url=http%3a%2f%2fen.wikipedia.org%2fwiki%2fFile%3a2006VW139.gif)
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