Sometimes, NASA gets to have a bit of fun -- with asteroids. This fall, the agency will have a grand ol' time with one such object called 2012 TC4, which will whizz past us at a comfortable distance of about 4,200 miles (6,800 kilometers) at its absolute closest. Since the asteroid is pretty small -- only about 30 to 100 feet (roughly nine to 30 meters) across -- this is the perfect chance for NASA's Planetary Defence Coordination Office to test out its techniques.