for National Geographic News
A giant asteroid named Apophis could be on a trajectory to careen into Earth in 2036. That was the prediction NASA scientists made in 2004, suggesting a 1 in 37 chance that the space rock would hit our planet.
The danger has since receded—the revised likelihood that Apophis will hit Earth is 1 in 45,000. But the close call has galvanized efforts among scientists to predict and hopefully prevent a potentially apocalyptic impact.
A slate of new proposals for addressing the asteroid menace was presented today at a meeting of the American Association for the Advancement of Science in San Francisco.
The aim, researchers said, is to defend the planet from an asteroid strike such as the one that slammed into Mexico's Yucatán peninsula some 65 million years ago—a cataclysmic event that many scientists think caused the extinction of the dinosaurs.
"There are 127 near-Earth objects we know about that have some chance of hitting us," said Russell Schweickart, a former Apollo astronaut and founder of the Houston, Texas-based Association of Space Explorers.
"You have to act when it looks like things are going to happen. If you wait until you're certain, it's going to be too late."
"Gravity Tractor," Super Scopes
Edward Lu, an astronaut and physicist at NASA, has developed a novel way to nudge off course any asteroids that appear to be headed for Earth.
Lu's proposed "gravitational tractor" is a spacecraft so massive—up to 20 tons (18 metric tons)—that it could divert an asteroid's path just by thrusting its engines in a specific direction while in the asteroid's vicinity.
"You don't aim your engines at the asteroids, you aim them to the side," he said. "That enables you to tow the asteroid just by the force of gravity."
In order for the gravitational tractor to work effectively, Lu said, international authorities would have to decide to use it long before an anticipated impact.
"You want many years or even decades of notice," he said. "It's like billiards—when you make a slight change before the bank shot, it creates a big change [in where the ball goes]."
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