Earth's Trojan Asteroid

Trojan asteroid: NASA has discovered that Earth has an asteroid companion traveling just ahead of our planet as it orbits the sun. This so-called Trojan asteroid could serve as a stepping stone to celestial objects farther afield

The asteroid, called 2010 TK7, is nearly 1,000 feet (300 meters) across and currently leading the Earth by about 50 million miles (80 million kilometers).

The asteroid is the first in a category known as Earth's Trojans, a family of space rocks that could potentially be easier to reach than the moon, even though its member asteroids can be dozens of times more distant, researchers said. Such asteroids, which have long been suspected but not confirmed until now, could one day be valuable destinations for missions, especially loaded as they might be with elements rare on Earth's surface, they added. [Photo and orbit of Asteroid 2010 TK7]

IN PICTURES: Asteroids

To imagine where Trojan asteroids are, picture the sun and Earth as being two points in a triangle whose sides are equal in length. The other point of such a triangle is known as a Trojan point, or a Lagrangian point after the mathematician who discovered them. The sun and Earth have two such points, one leading ahead of Earth, known as its L-4 point, and one trailing behind, its L-5 point.

The sun and other planets have Lagrangian points as well, and asteroids have been seen at those the sun shares with Jupiter, Neptune and Mars. Scientists had long suspected the sun and Earth had Trojans as well, but these companions would dwell mostly in the daytime sky as seen from Earth, making them largely hidden in the sunlight.

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