Lunar probe finishes main mission

BEIJING - China's second lunar probe, Chang'e-2, ceased orbiting the moon on Thursday afternoon after completing several preliminary missions and set off to explore outer space.

The lunar satellite is to travel 1.5 million kilometers away from the Earth's surface in at least 85 days, going to what is called a Lagrangian point, said Wang Xiaolei, deputy designer of the Chang'e-2 satellite.

Lagrangian points are locations in space where gravitational forces and the orbital motion of a body balance each other. They were discovered in 1772 by the French mathematician Louis Lagrange, who was working on a solution to the "three-body problem". The problem arose after scientists began wondering how a third, small body would orbit around two large bodies that are also in orbit.