3753 Cruithne is an asteroid in orbit around the Sun in 1:1 orbital resonance with that of the Earth. It is a periodic inclusion planetoid orbiting the Sun in an apparent horseshoe orbit. It has been called "Earth's second moon", although it is only a quasi-satellite.
Earth has a second moon, of sorts, and could have many others, according to three astronomers who did calculations to describe orbital motions at gravitational balance points in space that temporarily pull asteroids into bizarre orbits near our planet. Cruithne shares Earth's orbit, but does not actually orbit the Earth. The 5-km satellite, which takes 770 years to complete a horseshoe-shaped orbit around Earth, is called Cruithne and will remain in a suspended state around Earth for at least 5,000 years. Every 385 years, it comes to its closest point to Earth, some 15 million kilometres away. Its next close approach to Earth comes in 2285.
3753 Cruithne
Orbital characteristics
Orbit type
Near-Earth
Semimajor axis
0.99778 AU
Eccentricity
0.514784
Orbital period
365d 6h
Inclination
19.8122°
Physical characteristics
Diameter
5 km
Mass
? kg
Density
? g/cm3
Rotation period
?
Spectral class
?
Albedo
?
History
Discoverer
various, 1986
Cruithne, discovered in 1986, and then found in 1997 to have a highly eccentric orbit, cannot be seen by the naked eye. It is named after a Celtic tribe...
They were first Celtic racio-tribal group to come to the British Isles, appearing between about 800 and 500 B.C., and coming from the European continent. They were also known as the Picts. The correct pronunciation for 'Cruithne' is 'croo-een-ya'...