The possibility of a collision between Mars and an approaching asteroid has been effectively ruled out, according to scientists watching the space rock as it nears the Red Planet.
Tracking measurements of asteroid 2007 WD5 from four observatories have so greatly reduced uncertainties about its January 30 close approach to Mars that the odds of an impact have dropped to 1 in 10,000, the Near-Earth Object Program at NASA's Jet Propulsion Laboratory said in a posting on its Web site yesterday.
Scientists said the best estimate was for the asteroid to pass at a distance of more than 25,750 kilometers (16,000 miles) from the surface of Mars, or at worst, no closer than 3,990 kilometers (2,480 miles).
The asteroid was discovered in November. Initial observations of its orbit raised the odds of an impact to as high as 1 in 25 before further refinements came in.
The asteroid is big enough to blast a 800-meter (half-mile) wide crater if it struck the cold and dusty Martian surface, an event that astronomers would have liked to observe.
The NEO program normally looks for asteroids and comets that could pose a hazard to Earth.