NBC NEWS -- When the asteroid known as 2012 DA14 zooms within 17,200 miles of our planet on Friday, it'll mark the closest approach by a killer space rock in more than a century. Fortunately, the 150-foot-wide object will pose absolutely no risk to Earth — but over the course of millennia, other asteroids have literally rocked our world.
As safe as Friday's encounter will be, it's a reminder that Earth has been vulnerable to cosmic impacts in the past, and will continue to be in the future. That's why NASA and other agencies are spending millions of dollars to detect more of the estimated 1 million near-Earth objects that could be as threatening as 2012 DA14.
"We are looking at all kinds of partnership possibilities, across universities, space institutions and with the Air Force," said Lindley Johnson, program executive for the Near-Earth Object Observations Program at NASA Headquarters. This week, Johnson and other experts are gathering at a U.N.-sponsored conference in Vienna to discuss the creation of an international asteroid warning network.
Vienna is actually one of the places where 2012 DA14 can be seen in the night sky on Friday — not with the naked eye, but with binoculars or a small telescope. The best viewing opportunities will be available in Asia, Australia and Europe. (Follow the instructions at the bottom of this article to find out if it'll be visible from your location.)
The closest approach comes at 2:44 p.m. ET, when the asteroid will be zooming past at a speed of almost 17,500 mph, directly above the eastern Indian Ocean. It'll come 5,000 miles within the ring of communications satellites in geosynchronous Earth orbit, but those satellites are so widely distributed that experts say the chance of a collision is extremely remote.
If 2012 DA14 were on a collision course, the shock of its rapid fall through Earth's atmosphere would cause it to explode, unleashing the power of a 2.4-megaton atomic bomb. In the worst-case scenario, that'd be enough energy to destroy an entire city. A similar cosmic blast in 1908 laid waste to 820 square miles of Siberian forest in the Tunguska region.
It's possible that other such blasts have occurred over the course of Earth's history without being recorded. Based on a statistical analysis, NASA estimates that asteroids the size of 2012 DA14 strike Earth every 1,200 years or so. The only reason we know about this encounter is because the capabilities for tracking near-Earth objects have improved so much in recent years.
A Spanish observation team discovered 2012 DA14 just last year during a more distant flyby. "We probably would not have found DA14 10 years ago," said Don Yeomans, the head of NASA's Near-Earth Object Program Office at the Jet Propulsion Laboratory in Pasadena, Calif. Now that they know it's there, astronomers will be monitoring the asteroid with optical and radio telescopes, including the Arecibo Observatory's 1,000-foot-wide dish in Puerto Rico and NASA's Goldstone radio antenna in California.
Radar observations could provide insights into the space rock's shape and spin, while an analysis of the optical data could reveal what 2012 DA14 is made of. Think of Friday's encounter as a practice run for identifying and tracking the unknown asteroids that actually could threaten us in the years to come — and an incentive to figure out ways to deflect them in case we have to.