fr:Lune ast�ro�dale ja:小惑星の衛星 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. The term double asteroid is sometimes used for 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

External links

• Asteroids with Satellites (http://www.johnstonsarchive.net/astro/asteroidmoons.html)

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)