Page "Libration" Paragraph 8

In 1772 Lagrange's analyses determined that small bodies can stably share the same orbit as a planet if they remain near Lagrange points, which are 60 ° ahead of or behind the planet in its orbit.

Such ‘ trojan asteroids ’ have been found co-orbiting with Earth, Jupiter, Mars, and Neptune.

Trojan asteroids associated with Earth are difficult to observe in the visible spectrum, as their libration paths are such that they would be visible primarily in the daylight sky.

In 2010, however, using infrared observation techniques, the asteroid was found to be a trojan companion of the Earth ; it librates around the leading Lagrange point,, in a stable orbit.