FINAL BORDER: an asteroid nearly a mile wide with a moon of its own is expected to pass through Earth this weekend, traveling at 48,000 mph. The space rock, known as the 1999 KW4 asteroid, was discovered 20 years ago and is so large that it is orbited by a moon.
On Saturday night, 1999 KW4 will make its closest approach to Earth. It will be visible until May 27. Because it carries a large moon, 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 the 1999 KW4 as "slightly crushed at the poles and with a mountain ridge around the equator, which runs all the way around the asteroid." This ridge gives the primary a nut-like appearance or a spinning top. "
The asteroid was first discovered by the Lincoln Near Earth Asteroid Research Survey (LINEAR) in Socorro, New Mexico, according to NASA. The asteroid will not pass again near Earth until 2036.
The Center for Minor Planets of the Smithsonian Astrophysical Observatory has classified the 1999 KW4 as a "potentially dangerous 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, approximately 13 times the distance between Earth and the Moon.