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Protecting Earth from asteroids

Asteroid impacts with Earth are a near-certainty, scientists say. The question is: What, if anything, should we do to track asteroids and protect Earth from them?

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"The current near-Earth object surveys cannot meet the goals of the 2005 George E. Brown, Jr. Near-Earth Object Survey Act directing NASA to discover 90 percent of all near-Earth objects 140 meters in diameter or greater by 2020," the report states. Then the authors lay out a few options for getting the job done:

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If completion of the survey as close to the original 2020 deadline as possible is considered most important, a space mission conducted in concert with observations using a suitable ground-based telescope and selected by peer-reviewed competition is the best approach. This combination could complete the survey well before 2030, perhaps as early as 2022 if funding were appropriated quickly.
If cost conservation is deemed most important, the use of a large ground-based telescope is the best approach. Under this option, the survey could not be completed by the original 2020 deadline, but could be completed before 2030. To achieve the intended cost effectiveness, the funding to construct the telescope must come largely on the basis of non-NEO programs.

The report also calls on the US to lead the formation of an international body to monitor and deal with NEO threats.

According to experts cited by Space.com, NASA needs an additional $1 billion in funding over the next 15 years to attain its goal of cataloguing all potentially threatening asteroids. As of today, NASA's Near Earth Object Program is aware of and tracking 6,691 objects.

NASA estimates that every few million years, an asteroid comes along that could threaten civilization. Every 2,000 years, a football field-size meteor hits Earth, causing significant damage to the immediate area. Anything smaller than 25 meters will likely burn up in Earth's atmosphere.

But in 1908, something — probably a comet — exploded over the Siberia. It flattened 2,000 square kilometers (772 square miles) of forest in a largely uninhabited region.

Scientists assumed that the object was some 70 meters across. But new research indicates it might have been just 30 to 50 meters wide. And it still caused extensive damage. Objects of this size are thought to arrive every 300 years.

Because of the newfound importance of this size class, and relatively short interval at which they arrive, the authors of the report recommend that "surveys should attempt to detect as many 30- to 50-meter objects as possible."

Illustrating just how difficult asteroids are to detect, last week New Scientist reported that a 10-meter asteroid passed quite close to Earth — about one-third the distance between Earth and the moon. We noticed it only when it was three days out, far too late to head it off had it been on a collision course with Earth.

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