Editing Binary asteroid (section)

{{short description|System of two asteroids orbiting their common center of mass}}
{{See also|Minor-planet moon}}
[[File:243 ida crop.jpg|thumb|280px|Binary asteroid [[243 Ida]] with its small [[minor-planet moon]], [[Dactyl (moon)|Dactyl]], as seen by ''[[Galileo (spacecraft)|Galileo]]'']]
[[File:Didymos-Dimorphos true orientation.png|thumb|Binary near-Earth asteroid [[65803 Didymos]] and its moon [[Dimorphos]] imaged by the [[Double Asteroid Redirection Test]] spacecraft]]

A '''binary asteroid''' is a system of two [[asteroid]]s orbiting their common [[barycenter]]. The binary nature of [[243 Ida]] was discovered when the [[Galileo (spacecraft)|Galileo spacecraft]] flew by the asteroid in 1993. Since then [[List of minor-planet moons|numerous binary asteroids]] and [[Minor-planet moon#Triple systems|several triple asteroids]] have been detected.<ref>{{cite book |last1=Margot|first1=Jean-Luc|title=Asteroids IV|last2=Pravec|first2=Petr|last3=Taylor|first3=Patrick|last4=Carry|first4=Benoît|last5=Jacobson|first5=Seth |pages=355|arxiv=1504.00034 |date=2015|doi=10.2458/azu_uapress_9780816532131-ch019 |chapter=Asteroid Systems: Binaries, Triples, and Pairs|isbn=9780816532131|bibcode=2015aste.book..355M |s2cid=56278100 |editor1-last=Michel |editor1-first=Patrick |editor2-last=DeMeo |editor2-first=Francesca E. |editor-last3=Bottke |editor3-first=William F.}}</ref>

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 small [[minor-planet moon|moons]] – also called "companions" or simply "satellites" – include [[87&nbsp;Sylvia]], [[107&nbsp;Camilla]] and [[45&nbsp;Eugenia]] (all triples), [[121&nbsp;Hermione]], [[130&nbsp;Elektra]] (a quadruple), [[22&nbsp;Kalliope]], [[283&nbsp;Emma]], [[379&nbsp;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&nbsp;Antiope]], {{mpl-|300163|2006 VW|139}}, {{mpl|2017 YE|5}} and [[69230&nbsp;Hermes]], with average component diameters of 86, 1.8, 0.9 and 0.8&nbsp;km, respectively.

In August 2024 [[Gaia (spacecraft)|Gaia]] reported 352 new binary asteroid candidates.<ref>{{Cite journal |last=Liberato |first=L. |last2=Tanga |first2=P. |last3=Mary |first3=D. |last4=Minker |first4=K. |last5=Carry |first5=B. |last6=Spoto |first6=F. |last7=Bartczak |first7=P. |last8=Sicardy |first8=B. |last9=Oszkiewicz |first9=D. |last10=Desmars |first10=J. |date=August 2024 |title=Binary asteroid candidates in Gaia DR3 astrometry |url=https://www.aanda.org/10.1051/0004-6361/202349122 |journal=Astronomy & Astrophysics |volume=688 |pages=A50 |doi=10.1051/0004-6361/202349122 |issn=0004-6361|arxiv=2406.07195 }}</ref><ref>{{Cite web |last=Graham-Shaw |first=Kate |title=These 352 Asteroids Likely Have Cute Little Moonlets |url=https://www.scientificamerican.com/article/these-352-asteroids-likely-have-cute-little-moonlets/ |access-date=2024-08-14 |website=Scientific American |language=en}}</ref>