NASA is one of those government agencies that never gets enough credit. Well, maybe the revelation that the Earth had three moons in the past (possibly) will help NASA get the recognition it deserves:
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.
The 3-mile-wide (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.
Cruithne, discovered in 1986, and then found in 1997 to have a highly eccentric orbit, cannot be seen by the naked eye, but scientists working at Queen Mary and Westfield College in London were intrigued enough with its peregrinations to come up with mathematical models to describe its path.
For a less technical analysis of the theory that the Earth had three moons once, Fox News reports:
Prevailing scientific consensus holds that the existing Moon was formed when a Mars-sized planet collided with the Earth 4.5 billion years ago, when the solar system was very young.
So much matter would have been thrown up into space that it recollected under its own gravity to form the Moon, which for millions of years would have glowed red-hot as the molten rock from the planetary collision cooled.
However, researchers Jack J. Lissauer of NASA's Ames Research Center near Mountain View, Calif., and John E. Chambers of the Carnegie Institution of Washington figure quite a bit of that ejected matter would have recollected into two other small moons at the so-called "Lagrangian points" or "Trojan points."
Another good article about the 'earth had three moons' theory can be found at the New Scientist.