It's been a bad few weeks for folks inclined to worry. There was the North Korean nuclear test and the return of extreme weather to the Northeastern U.S., and then there was the matter of the possible end of Earth in the middle of February. As it turned out, we're still here--but we did get something of a wake-up call.
As NASA had been warning for a year, a 150-ft. asteroid ("the size of a small office building," as the space agency discomfitingly described it) was on track to buzz the planet at exactly 2:24 p.m. E.T. on Feb. 15, coming in at a relative treetop level of 17,200 miles. If you think that sounds pretty far away, think again. It's only one-fourteenth the distance to the moon and actually a few thousand miles below the altitude of our highest-flying satellites. And while a rock that size may be a flyspeck compared with the elephantine bulk of Earth, the energy it carries as it barrels in can do a lot of damage--on the order of 2.4 megatons, or 180 times the power of the Hiroshima bomb.
So the worriers had plenty of reason to wring their hands, right? Well, no--not this time, at least. The asteroid, known unartfully as 2012 DA14, was never going to hit us, something astronomers could determine almost immediately after it was discovered in 2011. But that rock has a whole lot of friends. It's just one of what are estimated to be up to 1 million potentially dangerous near-Earth objects (NEOs) out there, only 9,688 of which have been spotted and cataloged by astronomers so far. Of those, 1,377 are identified as potentially hazardous asteroids (PHAs), based on their size and their eventual proximity to Earth.
While most of these cosmic missiles fly harmlessly by, some do hit--and cataclysmically so. Our moon is thought to have been created when a Mars-size planetesimal collided with us more than 4 billion years ago. The dinosaurs were all but certainly wiped out by a 6-mile rock that landed off the Yucatán Peninsula about 65 million years back. As recently as June 30, 1908, an asteroid measuring 330 ft. exploded in the skies over the Tunguska region in Siberia, unleashing a four-megaton blast that leveled trees across an 825-mile expanse.
"We get 100 tons of interplanetary debris hitting the atmosphere every day," says Don Yeomans, head of the Near Earth Object Program Office at NASA's Jet Propulsion Laboratory. "Most of it is sand-size or pea-size, but we get a basketball-size object every day. Every few months we get one as big as a Volkswagen."
Even those car-size chunks incinerate before they hit the ground, but the bigger a piece of falling ordnance is, the likelier it is for some of it to survive--and probability alone says our planet is going to get clobbered again. Unlike the dinosaurs, we have the ability to see it coming and, at least in theory, defend ourselves. We don't have our asteroid shield in place yet, however, and the race is thus on to find--and stop--the next bullet before it finds us.
Rain of Rocks