from CBS News

A massive asteroid with its own moon trailing behind will pass by Earth this weekend

BY BRIAN PASCUS

1999 kw4 nasa
NASA rendering of KW4 1999 asteroid with moon following 

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.

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