 The possibility of a trojan planet to Kepler-91b was studied but the conclusion was that the transit-signal was a false-positive.One possibility for the habitable zone is a trojan planet of a giant planet close to its star.According to the giant impact hypothesis, the Moon formed after a collision between two co-orbital objects—Theia, thought to have had about 10% of the mass of Earth (about as massive as Mars), and the proto-Earth—whose orbits were perturbed by other planets, bringing Theia out of its trojan position and causing the collision.