Charles Bolden, the chief of the Nasa, has warned that the US space agency's best advice on how to handle a large asteroid heading towards New York City is "pray".
By Reuters in Cape Canaveral, Florida, edited by Sarah Titterton
9:00PM GMT 20 Mar 2013
Mr Bolden told US lawmakers that prayer was all that the US or anyone could currently do about unknown asteroids and meteors that may be on a collision course with Earth.
An asteroid estimated to be have been about 55 feet (17 metres) in diameter exploded on Feb 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 (27,681 km) from Earth, closer than the network of television and weather satellites that ring the planet.