Asteroid Big Enough to Take Out a Metro Area Passes Close to Earth

You're safe -- the asteroid known as 2000 EM26 did not hit Earth Monday night. Scientists predicted it wouldn't. But by interstellar standards, this block of rock the length of three football fields was on our front porch.

As our cover story "Space Invader" explains this week, these so-called near-Earth objects (NEOs) are much more common, more potentially hazardous, and just plain more interesting than people realized a few decades ago. That's why the University of Arizona is leading a program to launch a spacecraft in 2016 that will land on an asteroid -- for five seconds -- and retrieve a sample that later will be analyzed on Earth.

See also: -Asteroid That Might Hit Earth Next Century to Be Visited by U of A Spacecraft in 2018

Nothing has highlighted the risk of asteroids so perfectly in modern times as the fireball that exploded last February over Chelyabinsk, Russia, injuring more than 1,000 people from flying glass and heat burns. The object that caused the explosion was about 65 feet long.

The asteroid that passed "close" to Earth Monday night was large enough, in theory, to take out a metropolitan area like the Valley. Scientists estimate that 2000 EM26 was up to 270 meters -- or about 900 feet -- in diameter. It was 2 million miles away, about eight moon-lengths from Earth, at its nearest.

Close enough that scientists felt a thrill.

About 94 percent of the biggest asteroids in orbit around the sun near Earth are believed to have been found, their threat-levels categorized by NASA. According to NASA's website, there are 1,457 "potentially hazardous asteroids" -- and 2000 EM26 is one. That doesn't mean it ever will hit Earth, but it makes "threatening close approaches."

If it did hit, Purdue University's "Impact: Earth!" website shows just how bad the damage could be. Using the asteroid's estimated maximum size, you can see that from a distance of 10 miles, nearly everything on the ground is burned up and blown away. Even at 20 miles from the impact point, the site says, glass in windows would shatter and up to 30 percent of trees would be knocked over.

A more likely ocean impact of EM26, on the other hand, might cause little to no damage to people. As we covered this week, Jay Melosh, a Purdue astronomer who used to work for the University of Arizona, studied the problem of potential tsunamis due to asteroid strikes and concluded that fears were overblown.

Bennu, the asteroid to be studied by the UofA's OSIRIS-REx spacecraft, is 1,600 feet in diameter. Its orbital velocity is about 60,000 mph -- more than twice as fast as EM26. It would make a much bigger crater. And it has about a 1-in-1,400 chance of hitting Earth in the late 21st century, current NASA calculations show.

Studying Bennu will help prepare people to deflect one of these objects someday, perhaps with a nuclear-bomb-packed battering ram. The billion-dollar science project also will help people learn about the makeup of asteroids, advancing knowledge of the origin of the solar system.

Maybe in the far future, humans will use asteroids to obtain precious metals and as launching pads for deep-space exploration.

If a proverbial "planet-killing" asteroid doesn't get us first.

Got a tip? Send it to: Ray Stern.

Follow Valley Fever on Twitter at @ValleyFeverPHX. Follow Ray Stern on Twitter at @RayStern.

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Ray Stern has worked as a newspaper reporter in Arizona for more than two decades. He's won numerous awards for his reporting, including the Arizona Press Club's Don Bolles Award for Investigative Journalism.
Contact: Ray Stern