‘City-killer asteroid': 300-foot space rock flew by Earth ‘too close for comfort,' astronomers say

A “city killer” asteroid over 300 feet wide raced by Earth closer than the distance of the Moon on Thursday, astronomy experts said. 

Professor Michael Brown, of Monash University's school of physics and astronomy, told the Sydney Morning Herald that the asteroid -- named 2019 OK — came within 43,500 miles of Earth. The distance from the Earth to the Moon is about 239,000 miles, according to NASA. 

NASA's Jet Propulsion Laboratory also confirmed the discovery, the report said. 

"This is one of the closest approaches to Earth by an asteroid that we know of. And it’s a pretty large one," Brown said.

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"It’s impressively close. I don’t think it’s quite sunk in yet. It’s a pretty big deal," he said. "[If it hit Earth] it makes the bang of a very large nuclear weapon – a very large one."

Alan Duffy, Swinburne University astronomer and associate professor, told the Herald that "it would have hit with over 30 times the energy of the atomic blast at Hiroshima." 

"It's a city-killer asteroid. But because it's so small, it's incredibly hard to see until right at the last minute," Duffy said. "It's threading tightly between the lunar orbit. Definitely too close for comfort.“

Asteroids this size tend to fly by once every decade, the paper reported. 

Three other asteroids also raced past Earth on Thursday, but none of them were as close or as large as 2019 OK, the report said.

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Professor Gretchen Benedix, a planetary science researcher at Curtin University, told the Herald about the impact that the asteroid could make. 

"If that were to hit the Earth, that would be bad. Something 100 metres (328 feet) across would leave a noticeable hole on the planet," Benedix said.  

But 2019 OK will be back. 

NASA's Close Approach Data shows that it will pass by Earth multiple times through 2173, but none are expected to be remotely as close as Thursday's fly-by, according to the Herald.