Discovery Milestones
As of January 2012, over 200 minor-planet moons had been discovered, 76 in the asteroid belt (5 with two satellites), 4 Jupiter trojans, 37 to 41 near-Earth objects and 9 Mars-crossers. There are also 76 known moons of trans-Neptunian objects.
As early as 1978, following a stellar occultation, 532 Herculina had been suggested to have a moon and there were reports of other asteroids having companions (usually referred to as satellites) in the following years. A letter in Sky & Telescope magazine at this time pointed to pairs of large craters (e.g. the Clearwater Lakes in Quebec) also suggesting asteroids having companions.
However, it was not until 1993 that the first asteroid moon was confirmed when the Galileo probe discovered Dactyl orbiting 243 Ida. The second was discovered around 45 Eugenia in 1998. In 2001, 617 Patroclus and its same-sized companion Menoetius became the first known binary system in the trojan population. The first trans-Neptunian binary, 1998 WW31 was optically resolved in 2002.
Read more about this topic: Minor-planet Moon
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