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Asteroid moon
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Asteroid moon

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. An asteroid whose moon is roughly the same size as the asteroid itself may be referred to as a binary asteroid.

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 each other.

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 20 810
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

The Minor Planets
Vulcanoids | Main belt | | Near-Earth objects | Jupiter Trojans
Centaurs | Trans-Neptunians | Damocloids | Comets | Kuiper Belt | Oort Cloud
(For other objects and regions, see: , Asteroid moons and the Solar system)
(For a complete listing, see: List of asteroids)