An asteroid moon is an asteroid that orbits another asteroid. It is thought that many asteroids may possess moons, in some cases quite substantial in size. Asteroids with moons are commonly referred to as binary asteroids, although that term technically refers only to those systems in which the asteroid and its moon are roughly the same size.
The origin of asteroid moons is not currently known with certainty, and a variety of possibilities exist. A widely accepted theory is that asteroid moons are formed from debris knocked off of the primary asteroid by an impact.
The first asteroid moon to be identified was Dactyl which orbits 243 Ida. It was discovered by the Galileo probe in 1993. The second was discovered around 45 Eugenia in 1998. As of February 2004, nearly 37 more asteroid moons had been discovered by Earth-bound telescopes. Asteroid moons have been discovered orbiting main belt asteroids, Trojan asteroids, near-Earth objects, and Kuiper Belt objects.
An example of a binary asteroid is 90 Antiope, where two equal-sized components orbit the common centre of gravity.
Notable double asteroids
|Name||Orbital type||Diameter (km)||Name of moon||Diameter of moon (km)||Distance between pair (km)|
|22 Kalliope||main belt||181||S/2001 (22) 1 Linus||38||1,063|
|45 Eugenia||main belt||215||S/1998 (45) 1 Petit-Prince||13||1,190|
|87 Sylvia||main belt||261||S/2001 (87) 1||15||1,370|
|90 Antiope||main belt||85||S/2000 (90) 1||85||170|
|107 Camilla||main belt||223||S/2001 (107) 1||9||1,000|
|121 Hermione||main belt||209||S/2002 (121) 1||13||795|
|243 Ida||main belt||108||S/1993 (243) 1 Dactyl||1.4||108|
|283 Emma||main belt||148||S/2003 (283) 1||12||370|
|617 Patroclus||Jupiter Trojan||105||S/2001 (617) 1||95||610|
|762 Pulcova||main belt||137||S/2000 (762) 1||20||810|
|1509 Esclangona||main belt||12||S/2003 (1509) 1||4||140|
|3671 Dionysus||near-Earth asteroid||7||S/1997 (3671) 1||0.4||140|
|3749 Balam||main belt||1.5||S/2002 (3749) 1||1.5||350|
|(26308) 1998 SM165||TNO||465||S/2001 (26308) 1||180||6,000|
|(47171) 1999 TC36||Plutino||680||S/2001 (47171) 1||290||8,000|
|(66391) 1999 KW4||near-Earth asteroid||1.2||S/2001 (66391) 1||0.4||2.2|
- Asteroids with Satellites
|The Minor Planets|
|Vulcanoids | Main belt | Groups and Families | Near-Earth objects | Jupiter Trojans|
|Centaurs | Trans-Neptunians | Damocloids | Comets | Kuiper Belt | Oort Cloud|
|(For other objects and regions, see: Binary asteroids, Asteroid moons and the Solar system)|
|(For a complete listing, see: List of asteroids)|