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An Asteroid Big Enough to Wipe Out a City Nearly Hit Earth Last Week

The rock shot past at about a fifth of the distance to the Moon—and almost nobody saw it coming until just hours before it passed.
July 29, 2019, 6:12am
Asteroid approaches Earth
Image via Pixabay

Last Thursday, at about 11:22 AM (Australian eastern standard time), an asteroid big enough to wipe out a city streaked past Earth, only hours after it was first observed. "Asteroid 2019 OK," as the rock is called, is believed to be between 57 and 130 metres in diameter, and it passed Earth by just 70,000 kilometres—about a fifth of the distance to the Moon, and something of a near miss as far as cosmic encounters go. But most importantly, astronomers had no idea it was there until it nearly hit us, according to Fairfax.

“It snuck up on us pretty quickly. People are only sort of realising what happened pretty much after it’s already flung past us,” Michael Brown, an associate professor at Melbourne’s Monash University’s School of Physics and Astronomy, told The Washington Post. Speaking to The Sydney Morning Herald, he described the asteroid’s proximity to Earth as “impressively close” and “a pretty big deal.”

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

Had it struck, Michael suggested, Asteroid 2019 OK would have created a blast the size of “a very large nuclear weapon—a very large one."

Alan Duffy, astronomer at Swinburne University, was slightly less vague in his assessment. "It would have hit with over 30 times the energy of the atomic blast at Hiroshima," he said. "It's a city-killer asteroid. But because it's so small, it's incredibly hard to see until right at the last minute."

The worrying thing about Asteroid 2019 OK is that it was big enough to qualify as a “city-killer,” yet small enough to avoid detection. More than 90 percent of the apocalyptically large asteroids have been logged and had their trajectories mapped by NASA, but the smaller ones are harder to spot. Another reason Asteroid 2019 OK went unnoticed was the fact that it approached from the direction of the sun, which rendered it a silhouette against the backdrop of space, and made it very difficult for telescopes to catch.

“It’s faint for a long time,” Michael said. “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 recognised then things happen quickly, but this thing’s approaching quickly so we only sort of knew about it very soon before the flyby.”

"It should worry us all quite frankly," said Alan. "It’s not a Hollywood movie. It is a clear and present danger."

Others have argued, however, that while Asteroid 2019 OK’s close brush may have rattled a few people, the danger isn’t acute enough to be a genuine cause for concern. Emily Lakdawalla, senior editor of the Planetary Society—a nonprofit foundation that promotes space exploration—said “it is zero percent danger to us.

“It’s the kind of thing where you learn about something that you didn’t know about, like things flying close by us, and your inclination is to be scared. But just like sharks in the ocean, they’re really not going to hurt you and they’re really fascinating to look at.”

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