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A little gentle persuasion might accomplish more than powerful missiles to keep the Earth safe from rogue asteroids. Instead of trying to blow up an oncoming space rock, all that’s needed is

a large enough spaceship to gradually tug the asteroid off course using the space-warping effects of gravity, NASA scientists reported Thursday in the journal Nature. “It will take a couple

of decades of advance notice,” said Edward Lu, a former astronaut and a researcher at Johnson Space Center in Houston. But “it’s not a very difficult spaceship to build. Everybody knows

it’s feasible.” The concept is similar to an earlier idea of sending a space tugboat to push the asteroid off course, except the gravity-well spaceship won’t have to touch the asteroid to

make it veer off course. Hovering a few hundred feet above the asteroid, the spaceship would use the force of gravity as a tow line to pull the asteroid off course just enough to miss Earth.

The idea relies on Albert Einstein’s theory that large objects warp the space around them, like a bowling ball sitting on a stretchy trampoline. “It’s a very small force,” Lu said. “But

over time it builds up.” Lu and colleague Stanley Love, an astronomer and astronaut at the Johnson Space Center, calculate it would require a 20-ton gravity “tractor” -- one-sixth as massive

as the space shuttle -- tugging for a year to safely deflect an asteroid more than 600 feet across. The gravity tractor would need about 20 years’ advance notice to intercept the asteroid

at a great enough distance from Earth so that only a small deflection would be needed. An asteroid that size would be a pebble next to the 5-mile-wide monster that wiped out the dinosaurs,

but it would still be able to devastate a metropolitan area the size of Los Angeles. MORE TO READ