WASHINGTON - For those worried about the end of the world, Congress this week provided a reason to relax - a little.
On the positive side: NASA has found 95 percent of the asteroids nearest Earth that are big enough to wipe out civilization - and none poses any immediate threat to humanity.
But before you breathe a sigh of relief, there's also this: NASA acknowledged that the agency has little idea about the location of so-called "city killers," asteroids smaller than the half-mile-wide "world enders" but still big enough to crater New York City if it were hit exactly right.
Worse, there's considerable question what NASA and the military could do if scientists did spot a killer rock hurtling toward Earth, officials said at a U.S. House science hearing.
"A big segment of the population thinks it's just a matter of calling Bruce Willis in," said U.S. Rep. Bill Posey, R-Fla., a reference to the popular movie "Armageddon."
"What would we do if you detected even a small one ... headed toward New York City in three weeks? What would we do? Bend over and what?" said Posey to laughter.
Replied NASA Administrator Charlie Bolden, "If it's coming in three weeks, pray."
Right now, he said, building a spacecraft to deflect the asteroid would take years, which is why Bolden and John Holdren, the top science adviser to the president, both used the hearing as a springboard to champion the White House plan to send NASA astronauts to an asteroid by 2025.
"That mission will benefit from current efforts to detect, track and characterize (near-Earth objects) by speeding the identification of potential targets for exploration," said Holdren in prepared remarks. "And ... such a mission will generate invaluable information for use in future detection and mitigation efforts."
Prompting the hearing - and another that took place Wednesday in the Senate - were two reminders last month about the dangers of rocks from outer space.
The first was the explosion of a 55-foot asteroid over Russia on Feb. 15 that injured more than 1,000 people. The second was another asteroid, about 150 feet in diameter, that passed within 17,000 miles of Earth.
Though encounters with asteroids this size are rare, Earth is pelted every day.
"Objects the size of a basketball arrive about once per day, and objects as large as a car arrive about once per week," Bolden said. These objects burn up in the atmosphere and are often seen as "shooting stars."
But bigger strikes can - and do - happen. In 1908, an asteroid about 160 feet in diameter knocked down millions of trees in Siberia, and scientists think a massive asteroid about 6 miles in diameter wiped out the dinosaurs 65 million years ago when it hit near what is now the Yucatan Peninsula.
Holdren said that strikes like the one that hit Siberia are expected to happen only once every 1,000 years. But, he added, "the potential consequences are so large that it makes us take the threat seriously."
Though NASA has found most of the biggest nearby asteroids, officials estimate they've identified 10 percent or fewer of those about 500 feet in diameter - big enough to "devastate the better part of a continent," Holdren said.
Bolden said that, with NASA's current budget, it would take until 2030 or later to catalog space rocks in this range. (NASA spent $7.8 million on near-Earth-object observations in 2011 and $20.4 million in 2012, according to agency documents).
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