![Didymos-Dimorphos true orientation](https://upload.wikimedia.org/wikipedia/commons/0/05/Didymos-Dimorphos_true_orientation.png)
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
In astronomy, the barycenter (or barycentre; ) is the center of mass of two or more bodies that orbit one another and is the point about which the bodies orbit. A barycenter is a dynamical point, not a physical object. It is an important conc ...
. The binary nature of
243 Ida
Ida, minor planet designation 243 Ida, is an asteroid in the Koronis family of the asteroid belt. It was discovered on 29 September 1884 by Austrian astronomer Johann Palisa at Vienna Observatory and named after a nymph from Greek mythology. ...
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 was ...
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 important ...
– also called "companion" or simply "satellite" – include
87 Sylvia,
107 Camilla,
45 Eugenia,
121 Hermione,
130 Elektra,
22 Kalliope
Kalliope ( ; minor planet designation: 22 Kalliope) is a large M-type asteroid from the asteroid belt discovered by J. R. Hind on 16 November 1852. It is named after Calliope, the Greek Muse of epic poetry. It is orbited by a small moon named Li ...
,
283 Emma,
379 Huenna
Huenna (minor planet designation: 379 Huenna) is a large asteroid orbiting in the asteroid belt. It is part of the Themis family, and thus a C-type asteroid and consequently composed mainly of carbonaceous material.
It was discovered by Auguste C ...
,
243 Ida
Ida, minor planet designation 243 Ida, is an asteroid in the Koronis family of the asteroid belt. It was discovered on 29 September 1884 by Austrian astronomer Johann Palisa at Vienna Observatory and named after a nymph from Greek mythology. ...
and
4337 Arecibo
4337 Arecibo ( ''prov. designation'': ) is a binary Themistian asteroid from the outer regions of the asteroid belt, approximately in diameter. It was discovered on 14 April 1985, by American astronomer Edward Bowell at the Anderson Mesa Statio ...
(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
Antiope (minor planet designation: 90 Antiope) is a double asteroid in the outer asteroid belt. It was discovered on October 1, 1866, by Robert Luther. In 2000, it was found to consist of two almost-equally-sized bodies orbiting each other. At a ...
, , and
69230 Hermes
69230 Hermes is a sub-kilometer sized asteroid and binary system on an eccentric orbit, classified as a potentially hazardous asteroid and near-Earth object of the Apollo group, that passed Earth at approximately twice the distance of the Moon on ...
, 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
The asteroid belt is a torus-shaped region in the Solar System, located roughly between the orbits of the planets Jupiter and Mars. It contains a great many solid, irregularly shaped bodies, of many sizes, but much smaller than planets, called ...
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
A trans-Neptunian object (TNO), also written transneptunian object, is any minor planet in the Solar System that orbits the Sun at a greater average distance than Neptune, which has a semi-major axis of 30.1 astronomical units (au).
Typically, ...
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 Yorp or YORP may refer to one of the following:
* 54509 YORP, an Earth co-orbital asteroid
*Yarkovsky–O'Keefe–Radzievskii–Paddack effect, a second-order variation on the Yarkovsky effect
*Yorps, friendly one-eyed Martians from the Commander Ke ...
. 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
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
Antiope (minor planet designation: 90 Antiope) is a double asteroid in the outer asteroid belt. It was discovered on October 1, 1866, by Robert Luther. In 2000, it was found to consist of two almost-equally-sized bodies orbiting each other. At a ...
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