By Irene Klotz

CAPE CANAVERAL, Florida (Reuters) - NASA chief Charles Bolden has advice on how to handle a large asteroid headed toward New York City: Pray.

That's about all the United States - or anyone for that matter - could do at this point about unknown asteroids and meteors that may be on a collision course with Earth, Bolden told lawmakers at a U.S. House of Representatives Science Committee hearing on Tuesday.

An asteroid estimated to be have been about 55 feet in diameter exploded on February 15 over Chelyabinsk, Russia, generating shock waves that shattered windows and damaged buildings. More than 1,500 people were injured.

Later that day, a larger, unrelated asteroid discovered last year passed about 17,200 miles from Earth, closer than the network of television and weather satellites that ring the planet.

The events "serve as evidence that we live in an active solar system with potentially hazardous objects passing through our neighborhood with surprising frequency," said Representative Eddie Bernice Johnson, a Texas Democrat.

"We were fortunate that the events of last month were simply an interesting coincidence rather than a catastrophe," said Committee Chairman Lamar Smith, a Texas Republican, who called the hearing to learn what is being done and how much money is needed to better protect the planet.

NASA has found and is tracking about 95 percent of the largest objects flying near Earth, those that are .62 miles or larger in diameter.

"An asteroid of that size, a kilometer or bigger, could plausibly end civilization," White House science advisor John Holdren told legislators at the same hearing.

But only about 10 percent of an estimated 10,000 potential "city-killer" asteroids, those with a diameter of about 165 feet have been found, Holdren added.

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Large asteroid heading to Earth? Pray, says NASA