"A recently discovered object sharing Earth's orbital path around the Sun could actually be a trojan asteroid, astronomers have found. If confirmed, it will be only the second object of its type identified to date, suggesting that there could be more of these hidden asteroids lurking in Earth's gravitational pockets. Trojan asteroids are space rocks that share the orbital path of larger planetary bodies in the Solar System, hanging out in gravitationally stable regions known as Lagrangian points. These are pockets where the gravitational pulls of the planet and the Sun balance perfectly with the centripetal force of any small body in that region to basically hold it in place. Each two-body system has five Lagrange points, as seen in the diagram at the link. There are five between Earth and the Moon; and another five between Earth and the Sun. These are really quite useful, actually – we can put spacecraft in them and be reasonably confident they will stay put. The James Webb Space Telescope, for instance, will be going in the Earth-Sun L2 Lagrangian."