NASA says it does not have enough funding to study all of the asteroids that could threaten Earth.
    
The National Academy of Sciences said Congress authorized that program, but money was never given for the project.

NASA said it needs about $800 million for better telescopes or a space observation station.
    
"NASA calculated that to spot the asteroids as required by law would mean spending about $800 million between now and 2020, either with a new ground-based telescope or a space observation system," said Lindley Johnson, NASA's manager of the near-Earth objects program.

"If NASA got only $300 million it could find most asteroids bigger than 1,000 feet across," he added.

They estimate about 20,000 Earth-threatening asteroids and comets that need to be watched.

Source: The Associated Press