An Asteroid with Its Own Moon Will Zip Past Earth Tonight

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Keep your eyes on the skies this Memorial Day weekend.

Two asteroids - one nearly a mile wide and another, smaller one orbiting it - are rocketing its way through out solar system, and will pass close to the Earth (in astronomical terms, at least) on May 25.

This “double asteroid” is a relatively uncommon sight, and the smaller, 0.3 mile wide space rock is being called an “asteroid moon” by some.

An animation shows what the orbit of a moon around asteroid 1999 KW4 looks like.

A rendering from NASA shows an almost mile-wide asteroid known as 1999 KW4 will pass by Earth on Saturday. (Courtesy: NASA)

Identified as 1999 KW4, this massive asteroid’s orbit will take it through Earth’s orbit of the sun as it travels between us and Venus, on its own circuit around the sun that it completes every 188 days.

Fortunately, space is really, really big: even though this enormous asteroid will cross the Earth’s orbit, there’s no danger of a collision. Asteroid 1999 KW4 is going to pass within roughly 3,200,000 miles of Earth at 7:05 p.m. on May 25. That distance is roughly 13.5 times further away than our own moon. So while that’s still awfully close considering the endless expanse of space, it’s still really, really far.

Sadly, due to the size of the asteroid and the distance involved, amateur astronomers aren’t likely to be able to make it out in the night sky. But you can still always wave hello even if you don’t spot it - I’m sure the giant space rock will still appreciate the gesture as it swings through our solar neighborhood.

For more info on the double asteroid, check out this website from