Scientists have known for many years that asteroids often follow planets, moving in the same orbit around the sun. These so-called "Trojan asteroids" have been spotted tagging alongside Jupiter, Mars, and Neptune.
Earth, however, was believed to be free of these celestial stalkers — until now. Astronomers from Athabasca University in Canada, using data from an infrared NASA telescope that's orbiting the Earth, discovered an asteroid tracking us from just 50 million miles away.