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A direct hit from a large asteroid wouldn't be pretty

A major asteroid safely passed us this week. Whew! Had it made impact it could have been just as bad as in a Hollywood movie.

Not a friendly visitor.

A big, peanut-shaped asteroid about 2,000 feet (610 meters) across slipped by Earth at a comfortable distance on Wednesday. But, had such a large space rock hit us, you wouldn't want to be anywhere near the impact.

Shock waves strong enough to rupture internal organs and insane wind blasts that could toss people around like plastic bags and flatten forests are just a few of the worst effects we might face, according to a new study published Wednesday in Geophysical Research Letters.

"The likelihood of an asteroid impact is really low," said lead author Clemens Rumpf, from the University of Southampton, in a news release. "But the consequences can be unimaginable."

The grim study ranked seven effects -- heat, pressure shock waves, flying debris, tsunamis, wind blasts, seismic shaking and cratering -- for asteroids of different sizes and determined which were the most and least deadly.

The biggest risk overall comes from air bursts, mostly because they can result from even the smallest asteroids included in the study model, which ranged from 15 to 400 meters (49 to 1,312 feet). Pressure shock waves are nearly as dangerous, which is consistent with the bolide that sent out a blast over Chelyabinsk, Russia. Many people were injured when shock waves shattered glass, a particular danger to those who may have been looking out their windows at the flash caused by the streaking meteor.

Seismic shaking, cratering and flying debris were of least concern, the study found. Rumpf was surprised to find that impact-caused tsunamis were only responsible for 20 percent of overall deaths in the model. He explains that while an ocean impact could trigger such a wave, land impacts were found to be much more lethal overall.

But Rumpf's model used artificial asteroid impacts peppered at random spots around the globe. What if the worst case scenario came to pass and a densely populated city took a direct hit?

Not surprisingly, an even more grim, informal analysis was released this week by (After all, the site says part of being prepared is to have the right insurance.) It looked at what would happen if some of the US' most populous cities were hit by an asteroid. Turns out a lot of people would die. Again, though, big impacts are rare.

The site found that if a 984-foot asteroid like 2015 BN509 hit San Francisco head on, over 7 million lives could be lost. Such a massive impact could cause buildings to collapse within a 69-mile radius, and, given the seismic activity Northern California is known for, it might trigger earthquakes, unleashing even more destruction.

An even deadlier scenario imagines the asteroid that gave us a pass this week, 2014 JO25, making a direct hit on Chicago. The heat alone from the impact could stretch across the region to Grand Rapids, Michigan; Cedar Rapids, Iowa; Milwaukee; Indianapolis; Louisville, Kentucky; and St. Louis, with a total death toll of over 9.5 million.

Fortunately, and despite what any time-traveling, super-intelligent dinosaurs with vocal cords might tell you, big asteroid impacts are rare. We're struck by an asteroid over 60 meters (197 feet) every 1,500 years, and the catastrophic collision imagined for Chicago is likely to hit us no more often than every 100,000 years.

Still, next time you see a fireball in the sky, you may want to step away from the window and head for the basement, just in case. At least that's the advice I got from the Time Lord pteranodon I met.

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