Not A Moon, Not An Asteroid, Cruithne Is…What?

An article in the Ottawa Citizen this week discusses the Canadian discovery of several unique objects in the solar system. The first one discovered is now called Cruithne (pronounced Croo-een-ya), which is a name of a legendary Scottish king, and it has a similar sister discovered this year known for now only as 2002AA29. What’s special about these objects is their path of motion. Asteroids and planets go around and around the Sun. Artificial and natural satellites like The Moon go around and around the Earth and other planets. Cruithne follows neither a path solely around the Sun or a path solely around a planet. Thus it is neither planet, moon nor asteroid, but something following a horseshoe – shaped path through the solar system so unique there is no word defined in English for it. The gravity of the Earth is what mathematically causes this strange motion, so in that sense it Cruithne is a “companion” of Earth. Understanding the math of such orbital dances is the key to laying out more efficient space missions using techniques like the gravity slingshot, which can get you where you want to go in the Solar System via pinball-like detours years ahead of a direct flight to your target…