2010 TK7 is a sub-kilometer Near-Earth asteroid and the first Earth trojan discovered; it precedes Earth in its orbit around the Sun. Trojan objects are most easily conceived as orbiting at a Lagrangian point, a dynamically stable location (where the combined gravitational force acts through the Sun's and Earth's barycenter) 60 degrees ahead of or behind a massive orbiting body, in a type of 1:1 orbital resonance. In reality, they oscillate around such a point. Such objects had previously been observed in the orbits of Mars, Jupiter, Neptune, and the Saturnian moons Tethys and Dione.
Asteroid 2010 TK7 (circled in green) in image from the WISE spacecraft
2010 TK7's spiraling path (green) relative to Earth and its orbit (blue dots) over the course of half a tadpole loop; each spiral turn represents a year's motion
An Earth trojan is an asteroid that orbits the Sun in the vicinity of the Earth–Sun Lagrangian points L4 (leading 60°) or L5 (trailing 60°), thus having an orbit similar to Earth's. Only two Earth trojans have so far been discovered. The name "trojan" was first used in 1906 for the Jupiter trojans, the asteroids that were observed near the Lagrangian points of Jupiter's orbit.
2010 TK7, one of the two known Earth trojans, is located at the lower right, circled by a small green ring.
Illustration of Trojan Asteroid 2020 XL5
