An asteroid estimated to be upwards of 300 feet wide — the size of a football field — has been circling Earth for about 50 years but was only discovered this year by the Pan-STARRS 1 asteroid survey telescope, NASA announced this week. The asteroid has been dubbed 2016 HO3, and scientists say similar objects may be circling the planet without us knowing. Although such an asteroid could do major damage to Earth if it hit, NASA says it keeps a safe distance.
This NASA video gives more details