NASA announced that it has discovered that Earth is sharing its orbit with an asteroid as they both circle the sun. This "Trojan" asteroid called 2010 TK7 is about 1,000 meters in diameter and is about 50 million miles away. Scientists say that it's not a threat - it won't come any closer than 15 million miles in the next 100 years. Here's an animation showing the orbits of the Earth and its asteroid.
The discovery was made by NASA's NEO Observation Program which it funded to process data from the Wide-field Infrared Survey Explorer (WISE) mission. NEOWISE studies near-Earth objects (NEO) such as asteroids.
Scientists had believed that there were Trojan asteroids within Earth's orbit but they were too small and appeared near the sun from the Earth's point of view until now.
Image credit: Paul Wiegert, University of Western Ontario, Canada