Asteroid from ‘out of nowhere’ zipped past planet, scientists say

Alan Duffy was confused. On Thursday, the astronomer’s phone was flooded with calls from reporters wanting to know about a large asteroid that had just whizzed past Earth, and he couldn’t figure out “why everyone was so alarmed.”

“I thought everyone was getting worried about something we knew was coming,” said Duffy, who is also lead scientist at the Royal Institution of Australia.

Forecasts had already predicted that a couple asteroids would be passing relatively close to Earth this week.

Then he looked up the details of the hunk of 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,” said Michael Brown, a Melbourne-based observational astronomer.

According to data from NASA, the craggy rock was large, roughly 110 yards wide, and moving quickly along a path that brought it within about 45,360 miles of Earth. That’s about 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 with Australia’s Monash University’s School of Physics and Astronomy. “People are only sort of realizing what happened pretty much after it’s already flung past us.”

The asteroid’s presence was discovered only earlier this week by separate astronomy teams in Brazil and the United States.

Information about its size and path was announced just hours before it rocketed past Earth, Brown said.

“It shook me out my morning complacency,” he said. “It’s probably the largest asteroid to pass this close to Earth in quite a number of years.”

So how did the event almost go unnoticed?

First, there’s the issue of size, Duffy said. Asteroid 2019 OKis a sizable chunk of rock, but it’s nowhere near as big as ones capable of causing an event like the dinosaurs’ extinction. More than 90% of those asteroids, which are 0.62 miles or larger, have been identified by NASA and its partners.

“Nothing this size is easy to detect,” Duffy said of the 110-yard-wide asteroid. “You’re really relying on reflected sunlight, and even at closest approach it was barely visible with a pair of binoculars.”

Brown said the asteroid’s “eccentric orbit” and speed were also likely factors in what made spotting it ahead of time challenging.

Its “very elliptical orbit” takes it “from beyond Mars to within the orbit of Venus,” which means the amount of time it spends near Earth where it is detectable isn’t long, he said.

As it approached Earth, the asteroid was traveling at about 15 miles per second, he said. By contrast, other recent asteroids that flew by Earth clocked in at between 2.5 and 12 miles per second.

Duffy said astronomers have a nickname for the kind of space rock: “city-killer asteroids.”

If the asteroid had struck Earth, most of it would have likely reached the ground resulting in devastating damage, Brown said.

“It would have gone off like a very large nuclear weapon” with enough force to destroy a city, he said.

“Many megatons, perhaps in the ballpark of 10 megatons of TNT, so something not to be messed with,” he said.

In 2013 a significantly smaller meteor, about 22 yards across, broke up over the Russian city of Chelyabinsk and unleashed an intense shock wave that collapsed roofs, shattered windows and left about 1,200 people injured. The last space rock to strike Earth similar in size to Asteroid 2019 OK was more than a century ago, Brown said. That asteroid, known as the Tunguska event, caused an explosion that leveled nearly 500,000 square acres of forest land in Siberia.