A binary system is defined as two celestial objects close enough to orbit each other, according to NASA.
The Las Cumbres Observatory describes 1999 KW4 as “slightly squashed at the poles and with a mountain ridge around the equator, which runs all the way around the asteroid. This ridge gives the primary an appearance similar to a walnut or a spinning top.”
The asteroid was first discovered by the Lincoln Laboratory’s Near Earth Asteroid Research survey (LINEAR) in Socorro, New Mexico, according to NASA. The asteroid won’t pass this close to earth again until 2036.
The Smithsonian Astrophysical Observatory’s Minor Planet Center has classified 1999 KW4 as a “potentially hazardous asteroid” because it will travel relatively close to Earth. Even so, the asteroid will only pass as close as 3.2 million miles from Earth — roughly 13 times the distance between the Earth and the moon.