An asteroid nearly a mile wide with a moon of its own is expected to pass by Earth this weekend, traveling at 48,000 mph. The space rock, known as asteroid 1999 KW4, was discovered 20 years ago and is so large that it is orbited by a moon.
On Saturday evening, 1999 KW4 will make its closest approach to Earth. It will be visible until May 27. Because it carries a large moon along with it, the asteroid is technically designated as a binary system.
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.