On February 22, 2012, a telescope in Spain discovered an asteroid, 150 feet across, in an orbit that would bring it uncomfortably close to earth. Astronomers reassured us that we would be safe — this time — but that it was "a wakeup call for the importance of defending the Earth from future asteroid impacts." Last month, that asteroid, named 2012 DA14, passed within 17,200 miles of earth at a speed of nearly 17,500 miles per hour. That's a hair’s breadth in cosmological terms — it actually flew under the ring of communications satellites orbiting earth before it headed safely back out into space.
Earth isn't always so lucky. Ironically, on the same day that 2012 DA14 flew by, a meteorite struck outside the remote Russian town of Chelyabinsk with the power of 30 atomic bombs. Amazingly, no one was killed. A century ago, a meteor broke up with similar force over Russia's Tunguska forest, flattening an estimated 80 million trees.