To read an article entitled, Earth's Little Sidekick: A Tugboat Asteroid at the Time Magazine website please click on the link below. This article discusses the fact that Astronomers have discovered Earth's first Trojan asteroid — a rock that shares our own solar orbit, leading us around the sun.
Read more: http://www.time.com/time/health/article/0,8599,2085982,00.html#ixzz1TpX67NwI
In astronomy, a Trojan is a minor planet or natural satellite (moon) that shares an orbit with a larger planet or moon, but does not collide with it.
The asteroid is gray and its extreme orbit is shown in green. Image credit: Paul Wiegert, University of Western Ontario, Canada
To develop a better understanding of Trojan planets please visit the following website:
Why haven't astronomers been able to find more trojan asteroids around the Earth? The answer is:
"These asteroids dwell mostly in the daylight, making them very hard to see," said Martin Connors from Athabasca University in Canada." "But we finally found one because the object has an unusual orbit that takes it farther away from the Sun than what is typical for Trojans. WISE was a game-changer, giving us a point of view difficult to have at Earth's surface." (source: http://www.astronomy.com/~/link.aspx?_id=a950a757-d6b5-4b31-99b1-a667175e26a1 )
Here is a video about this finding (source:http://www.5min.com/Video/Trojan-Asteroid-Found-Near-Earth-517134289)