On Monday, an asteroid zoomed past the Earth, coming closer to our home planet than the moon orbits around it. The asteroid, which was about the size of a 10-story building, didn’t hit the Earth — which is a pretty good thing since astronomers didn’t even know it existed until Saturday — just two days earlier.

The asteroid, 2017 AG13, is between 36 and 111 feet long. It flew by the Earth at 7:47 a.m. EST, coming within about half of the distance from the Earth to the moon (around 100,000 miles) at its nearest point. The asteroid was traveling pretty fast too, zipping through the solar system at a spritely 9.9 miles per second.

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The University of Arizona’s Catalina Sky Survey only discovered 2017 AG13 on Saturday. This asteroid travels around the sun in an elliptical orbit, according to scientists, and on this pass, it crossed the orbits of both Earth and Venus. Experts could be forgiven for not spotting this one until the last minute, though. there are millions of asteroids out there, and we only have tabs on a few thousand of them — luckily, we’re tracking the biggest, most apocalyptic ones, and they’re not about to hit us. (Or at least we hope we’re tracking all of them).

Had 2017 AG13 hit Earth, we would’ve been fine. As Business Insider notes, Purdue University’s Impact Earth simulator predicts that an asteroid even on the larger side of 2017 AG13’s range would’ve exploded about ten miles above the surface, assuming it entered the atmosphere at a 45-degree angle. That would’ve released about 700 kilotons of energy, but at that height, all folks on the ground would have to deal with would be a loud, harmless boom.

Photos via NASA