Nasa is supposed to seek out almost all the asteroids that threaten Earth but lacks the money to do the job, a United States federal report says.
That is because even though Congress assigned the space agency this mission four years ago, it never gave Nasa money to build the necessary telescopes, says the report by the National Academy of Sciences.
Specifically, Nasa has been ordered to spot 90 per cent of potentially deadly rocks hurtling through space by 2020.
The agency estimates that there are about 20,000 asteroids and comets in Earth's solar system bigger than 140m in diameter.
So far, scientists know where about 6000 of the objects are.