Scientists almost didn’t detect ‘city-killer asteroid’ that whizzed past Earth
Alan Duffy was confused. On Thursday, the astronomer’s phone was suddenly 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,” Duffy, who is also lead scientist at the Royal Institution of Australia, told The Washington Post. Forecasts had already predicted that a couple asteroids would be passing relatively close this week.
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 Post. According to data from NASA, the craggy rock was large, roughly 100 metres wide, and moving quickly along a path that brought it within about 73,000 kilometres 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 of 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 OK is a sizable chunk of rock, but it’s nowhere near as big as the ones capable of causing an event like the dinosaurs’ extinction. More than 90 per cent of those asteroids, which are one kilometre or larger, have already been identified by NASA and its partners.
“Nothing this size is easy to detect,” Duffy said of the 100-metre-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 travelling at about 24 kilometres per second, he said. By contrast, other recent asteroids that flew by Earth clocked in at between four and 20 kilometres per second.
“It’s faint for a long time,” Brown said of Asteroid 2019 OK. “With a week or two to go, it’s getting bright enough to detect, but someone needs to look in the right spot. Once it’s finally recognized then things happen quickly, but this thing’s approaching quickly so we only sort of knew about it very soon before the flyby.”
The last-minute detection is yet another sign of how much still remains unknown about space and a sobering reminder of the very real threat asteroids can pose, Duffy said.
“It should worry us all, quite frankly,” he said. “It’s not a Hollywood movie. It is a clear and present danger.”