Minor-planet moon

A minor-planet moon is an astronomical object that orbits a minor planet as its natural satellite.

For example, in 1978, stellar occultation observations were claimed as evidence of a satellite for the asteroid to 532 Herculina.

A letter by astronomer Thomas Hamilton in the Sky & Telescope magazine at this time pointed to apparently simultaneous impact craters on Earth (for example, the Clearwater Lakes in Quebec), suggesting that these craters were caused by pairs of gravitationally bound objects.

[10] In 2001, 617 Patroclus and its same-sized companion Menoetius became the first known binary asteroids in the Jupiter trojans.

[1] The following table lists all satellites of multiple systems, starting with Pluto, which was unnumbered when its first moon was discovered in 1978.

In addition to the inevitable observational bias (dependence on the distance from Earth, size, albedo and separation of the components) the frequency appears to be different among different categories of objects.

The origin of minor-planet moons is not currently known with certainty, and a variety of hypotheses exist.

One such model is that minor-planet moons are formed from debris knocked off the primary by an impact.

Formation by collision is constrained by the angular momentum of the components, i.e. by the masses and their separation.

Distant binaries however, with components of comparable size, are unlikely to have followed this scenario, unless considerable mass has been lost in the event.

The distances of the components for the known binaries vary from a few hundreds of kilometres (243 Ida, 3749 Balam) to more than 3000 km (379 Huenna) for the asteroids.

The following binaries are double asteroids, with similarly sized components, and a barycenter outside of the larger object.

In addition, these bodies might be double asteroids, but due to errors in their size and orbit, it is uncertain.