Asteroids (minor planets) are small rocky objects that orbit the Sun. They are mainly located between the orbits of Mars and Jupiter, but some asteroids cross, or orbit near Earth’s orbit.
Research made by astronomers at Armagh Observatory, Armagh, Northern Ireland, showed that a newly discovered small asteroid, technically designated 2010 SO16 (approximately 400 m wide), has been found to be trailing Earth, along an orbit that is closely similar to that of Earth. Intriguingly, however, to an Earth-based observer, the path of 2010 SO16 looks very odd, resembling a gigantic horseshoe or letter “C”. This is due to the gravitational influence of Earth, which modifies the speed and trajectory of its new cosmic companion, when the two objects are closely spaced.
Curious 2010 SO16 has been accompanying Earth in space, for at least 250,000 years. Its nearness to our planet does not pose any collision risk, since its minimum distance from Earth is about 50 times the average distance of the Moon from Earth (approximately 384,000 km). 2010 SO16 was initially detected by NASA's WISE space observatory, which explores the universe in infrared light, from Earth orbit, over 500 km high. Computations show that 2010 SO16 will remain in its orbit for at least 120,000 years!
Amazingly, 2010 SO16 is not unique! There are a few more asteroids, which follow similar horseshoe orbits, in Earth’s vicinity. The most remarkable of these asteroids is Cruithne (about 5 km across). (Its name comes from the Irish language.) It is classified as a “quasi satellite”, an object that orbits the Sun in approximately the same duration a planet lasts to complete one revolution around the Sun, and remains close to the planet for many orbits. Cruithne orbits the Sun every 364 days, or almost as long as Earth’s year!
References
NASA
www.nasa.gov/
Wikipedia