There are places in space where the gravitational tug between a planet and the Sun balance out, allowing other smaller bodies to remain stable. These places are called Lagrangian points. So-called Trojan asteroids have been found in some of these stable spots near Jupiter and Neptune.
Trojans share their planet's orbit and help astronomers understand how the planets formed and how the solar system evolved. Now Scott Sheppard at the Carnegie Institution's Department of Terrestrial Magnetism and Chad Trujillo* have discovered the first Trojan asteroid, 2008 LC18, in a difficult-to-detect stability region at Neptune, called the Lagrangian L5 point.