Does asteroid 3753 Cruithne orbit the Earth like a moon or satellite?
No. The asteroid’s behaviour is more complicated than that: it doesn’t orbit the Earth, but rather it shares the Earth’s orbit. The relationship of a moon to its planet is called a two-body because there are only two important players (ie. the moon and the planet). However, in the case of Cruithne, the Earth and the asteroid both share the same orbit about the Sun, but are choreographed in such a away as to remain stable and avoid colliding with each other. This is called a three-body relationship as there are three main players: the Earth, the asteroid and the Sun. Please see the 3753 Cruithne main page for more details on the asteroid’s motion. • When the asteroid gets close to the Earth, it starts moving away again. Why doesn’t the Earth’s gravity pull it right in? Non-technical answer: Any orbit is a balance between two competing forces: gravity, which pulls things together, and the speed of the bodies, which (if it is in the right direction) tends to make them move away from each
