On Monday at 7:47 A.M. EST, an asteroid thought to be between 36 and 111 feet wide passed roughly 120,000 miles from Earth -- and astronomers didn't spot it until Saturday. Smithsonian reports: According to astronomer Eric Edelman at the Slooh Observatory, 2017 AG13 is an Aten asteroid, or a space rock with an orbital distance from the sun similar to that of Earth. AG13 also has a particularly elliptical orbit, which means that as it circles the sun it also crosses through the orbits of both Venus and Earth. Lucky for us, 2017 AG13 wasn't a planet killer; according to Wall, the asteroid was in the size range of the space rock that exploded in Earth's atmosphere over Chelyabinsk, Russia, in February, 2013. According to Deborah Byrd at EarthSky, that meteor exploded 12 miles in the atmosphere, releasing 30 times the energy of the Hiroshima nuclear bomb. Not only did it break windows in six cities, it also sent 1,500 people to the hospital. That meteor also came out of the blue, and researchers are still trying to figure out its orbit and track down its origins. While 2017 AG13 would have caused minor damage if it hit Earth, the close call highlights the dangers of asteroids.