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A binary asteroid is a system of two
2006VW139.gif, Time-lapse video of binary main-belt comet (288P)
The double asteroid 90 Antiope - Eso0718a (no tagline).jpg, Artist's impression of the double asteroid 90 Antiope
A binary asteroid is a system of two asteroid
An asteroid is a minor planet of the inner Solar System. Sizes and shapes of asteroids vary significantly, ranging from 1-meter rocks to a dwarf planet almost 1000 km in diameter; they are rocky, metallic or icy bodies with no atmosphere. ...
s orbiting their common barycenter. The binary nature of 243 Ida was discovered when the Galileo spacecraft
''Galileo'' was an American robotic space probe that studied the planet Jupiter and its moons, as well as the asteroids Gaspra and Ida. Named after the Italian astronomer Galileo Galilei, it consisted of an orbiter and an entry probe. It wa ...
flew by the asteroid in 1993. Since then numerous binary asteroids and several triple asteroids have been detected.
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 a small minor-planet moon
A minor-planet moon is an astronomical object that orbits a minor planet as its natural satellite. , there are 457 minor planets known or suspected to have moons. Discoveries of minor-planet moons (and binary objects, in general) are importan ...
– also called "companion" or simply "satellite" – include 87 Sylvia, 107 Camilla, 45 Eugenia, 121 Hermione, 130 Elektra, 22 Kalliope, 283 Emma, 379 Huenna, 243 Ida and 4337 Arecibo (in order of decreasing primary size). Some binary systems have a mass ratio near unity, i.e., two components of similar mass. They include 90 Antiope, , and 69230 Hermes, with average component diameters of 86, 1.8, 0.9 and 0.8 km, respectively.
Description
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 large main-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
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 ...
, which orbit in the inner part of the Solar System, most likely form by spin-up and mass shedding, likely as a result of the YORP 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. This process also exposes fresh material at the poles of the asteroid.
Gallery
See also
* * *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 o ...
* Triple asteroids and
References
{{Small Solar System bodies