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Earth in crossfire on NASA hazardous asteroid map

Earth is near the center of a tangled mass of potentially hazardous asteroids. But there's little to worry about.

Asteroid map
The orbits of all known Potentially Hazardous Asteroids (PHAs) as of early 2013 are shown here. But none are worrisome threats over the next century.

If you've been watching the skies for the spectacle of the Perseid meteor shower over the past few days, you've probably thought about some of the larger rocks up above.

A few are downright scary compared to shooting stars. This graphic from NASA shows the orbits of more than 1,400 Potentially Hazardous Asteroids (PHAs), objects measuring at least 460 feet across that come within 4.7 million miles of Earth's orbit.

It looks like a giant Spirograph drawing with Earth near the center, but NASA assures us that these giant boulders of rock and ice are not "a worrisome threat" over the next 100 years.

Of course, 4.7 million miles is really, really far away -- about 20 times the distance to the moon. But not all PHAs have been found. As one looks further into the future, the orbits of known PHAs become less predictable.

"By continuing to observe and track these asteroids, their orbits can be refined and more precise predictions made of their future close approaches and impact probabilities," NASA's Jet Propulsion Laboratory reported on its Photojournal page.

The recent discovery of the 10,000th near-Earth object (NEO) highlighted that there are a lot of marbles zooming around up there. NEOs are defined as objects approaching the Earth's orbital distance to within some 28 million miles.

Of greatest concern are the roughly 900 near-Earth asteroids that are at least 1 kilometer (0.62 miles) across. Judging by studies of mass-extinction events of the past, an impact by one of these could be a real bummer.

On NASA's NEO Program Sentry Risk Table of more than 400 near-Earth asteroids, only one is flagged as a yawn-inducing green on the Torino Impact Hazard Scale.

The asteroid known as 2007 VK184 is believed to be about 430 feet across and presents an unlikely chance of hitting us in 2048. Further observations likely will reduce that chance to zero.

But the threat of a big hit has prompted some scientists to hatch plans to deflect or destroy dangerous space rocks by using everything from nuclear weapons to huge laser guns.

What do you think? Do asteroids concern you? Or is the danger far too miniscule to care about?