WASHINGTON — An asteroid half the size of a football field passed within an astronomical hair's breadth of Earth on Friday in the closest such encounter in a century.
The asteroid, called 2012 DA14, came within 17,200 miles of Earth at 2:25 p.m. EST, over Indonesia. Telescope images from western Australia, broadcast on NASA Television, showed the asteroid as a white speck against the blackness of space.
While DA14 didn't hit the planet, astronauts and interplanetary evangelists say its fly-by — and a meteor strike in Russia early Friday — serve as evidence that monitoring for risks from space objects must be increased.
"If this asteroid were to hit London, the entire metropolitan area would be gone," Sergio Camacho, head of the effort at the Vienna-based U.N. Office for Outer Space Affairs, said of DA14 in an interview.
In 1998, NASA began working on finding and tracking the largest asteroids, typically more than one kilometer in diameter and capable of destroying much of humanity. That's left a big gap in finding smaller objects that would demolish a city while sparing the rest of civilization.
NASA says it has found and mapped 1,310 of the largest, most dangerous "near-Earth objects." The total may account for less than 10 percent of all space threats, it says.
DA14 was discovered in February 2012 by a group of amateur astronomers at La Sagra Observatory in southern Spain. Jaime Nomen, a dental surgeon who dabbled in astronomy, said his group bought a high-powered telescopic camera and software with the help of a $7,695 grant in 2010 from the Planetary Society.
The probability of an asteroid hitting Earth is fairly low.
"If we're lucky, none of us will see an asteroid coming toward the Earth in our lifetime," Camacho said. "But if we're not lucky and we didn't do anything, the only thing we might be able to do is evacuate."