Asteroids are made up of materials dating back to the beginnings of our solar system and, when they orbit the sun on the same path as a planet, are classified as trojans. And much like the Trojan Horse of Greek mythology, they may harbor secrets inside. An international team of astronomers, supported in part by NSF, has confirmed only the second known Earth Trojan, which is designated 20-20 XL5.Learn more on NSF’s “The Discovery Files.”