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Huge asteroid zipping by Earth has its own moon

A space rock that could bigger than the Great Pyramid of Giza just flew by us, and it wasn't alone.

Near-Earth asteroid 2016 AZ8 and its companion captured by Arecibo radar.

Arecibo Observatory/NASA/NSF

The largest asteroid expected to pass by Earth this month has a traveling companion. 

Asteroid 2016 AZ8 made its nearest swing by our planet in the 21st century early Monday. As it was approaching, astronomers were able to take a closer look. Radar images of the space rock acquired using the huge Arecibo Observatory in Puerto Rico show it is actually a binary system -- the main asteroid is orbited by a smaller boulder.

According to Arecibo, the larger asteroid could be 420 meters (1,378 feet) in diameter, nearly as wide as the Pentagon's headquarters and bigger than the Great Pyramid of Giza. The "moon" satellite circling it at a distance of about 400 meters (1,312 feet) is estimated to be around 180 meters (591 feet) wide.

Fortunately there's no reason to be freaked out because this duo's visit was actually at a comfortable distance of over 4.3 million km (2.7 million miles). It's also not expected to come any closer to us until at least the 23rd century, at which point we could be ready to build a cosmic truck stop on its surface.