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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 Antiope90 Antiope is an asteroid discovered on October 1, 1866 by Robert Luther. The 90th asteroid to be discovered, it is named after an Amazon princess, sister of Hippolyte and daughter of Ares, who was taken prisoner by Heracles and later married Theseus., where two equal-sized components orbit the common centre of gravity.
| Name | Orbital type | DiameterIn geometry, a diameter of a circle is any straight line segment that passes through the center and whose endpoints are on the circular boundary, or, in more modern usage, the length of such a line segment. When using the word in the more modern sense, on ( kmA kilometre ( American spelling: kilometer (symbol: km is a unit of length equal to 1000 metres. It is approximately equal to 0. 621 miles, 1094 yards or 3281 feet. Slang terms for kilometre include " klick" (or "click") and "kay". Click" is also used for) | Name of Moon | Diameter of Moon ( kmA kilometre ( American spelling: kilometer (symbol: km is a unit of length equal to 1000 metres. It is approximately equal to 0. 621 miles, 1094 yards or 3281 feet. Slang terms for kilometre include " klick" (or "click") and "kay". Click" is also used for) | Distance between pair ( kmA kilometre ( American spelling: kilometer (symbol: km is a unit of length equal to 1000 metres. It is approximately equal to 0. 621 miles, 1094 yards or 3281 feet. Slang terms for kilometre include " klick" (or "click") and "kay". Click" is also used for) |
|---|---|---|---|---|---|
| 22 Kalliope22 Kalliope ("kuh LYE uh pee") is a very large Main belt asteroid discovered by J. Hind on November 16, 1852. It is named after Calliope, the Greek Muse of epic poetry. Kalliope is 181 km in diameter, and is a M-type asteroid, indicating fairly pure nicke | main beltThe asteroid belt is a region of the solar system falling roughly between the planets Mars and Jupiter where the greatest concentration of asteroid orbits can be found. It is termed the main belt when contrasted with other concentrations of minor planets, | 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 |