NASA is charged with spotting most of the asteroids that pose a threat to Earth but does not have the money to complete the job, a US government report said. That is because even though Congress assigned the space agency that mission four years ago, it never gave NASA the money to build the necessary telescopes, according to the report released Wednesday by the National Academy of Sciences. Specifically, the mission calls for NASA, by the year 2020, to locate 90 percent of the potentially deadly rocks hurtling through space. The agency says it has been able to complete about one-third of its assignment with the current telescope system. NASA estimates that there are about 20,000 asteroids and comets in our solar system that are potential threats. They are larger than 460 feet (140 meters) in diameter - slightly smaller than a sports stadium in New Orleans. So far, scientists know where about 6,000 of these objects are. Rocks between 460 feet and 3,280 feet (1,000 meters) in diameter can devastate an entire region, said Lindley Johnson, NASA's manager of the near-Earth objects program. Just last month astronomers were surprised when an object of unknown size and origin bashed into Jupiter and created an Earth-sized bruise that is still spreading. Jupiter does get slammed more often than Earth because of its immense gravity, enormous size and location. 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, Johnson said. If NASA got only $300 million it could find most asteroids bigger than 1,000 feet (300 meters) across, he said. But so far NASA has gotten neither sum. The space rocks astronomers are keeping a closest eye on are a 430-foot (130-meter) diameter object that has a 1-in-3,000 chance of hitting Earth in 2048 and a much-talked about asteroid, Apophis, which is twice that size and has a one-in-43,000 chance of hitting in 2036, 2037 or 2069. Last month, NASA started a new Web site for the public to learn about threatening near
