Then, he looked up the details of the hunk of space rock named Asteroid 2019 OK.

“I was stunned,” he said. “This was a true shock.”

This asteroid wasn’t one that scientists had been tracking, and it had seemingly appeared from “out of nowhere,” Michael Brown, a Melbourne-based observational astronomer, told The Washington Post. According to data from NASA, the craggy rock was large, an estimated 57 to 130 meters wide (187 to 427 feet), and moving fast along a path that brought it within about 73,000 kilometers (45,000 miles) of Earth. That’s less than one-fifth of the distance to the moon and what Duffy considers “uncomfortably close.”

“It snuck up on us pretty quickly,” said Brown, an associate professor in Australia with Monash University’s School of Physics and Astronomy. He later noted, “People are only sort of realizing what happened pretty much after it’s already flung past us.”