The first in a long-sought type of asteroid companion to Earth has now been discovered, a space rock that always dances in front of the planet along its orbital path, just beyond its reach, space.com reported Wednesday.
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).
Researchers said 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, it 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.
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, according to space.com.
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.
Now, with the aid of the Wide-field Infrared Survey Explorer (WISE) satellite launched in 2009, astronomers have discovered Earth's first probable Trojan, a rock that spends its time at the sun-Earth L-4 point, space.com said.