"We were the discoverer," said Sudbury of the Apollo Asteroid 2004 XP14, which passed 268,873 miles (some 432,000 kilometers) from the Earth at 0425 GMT.

The distance between the two bodies was slightly greater than that between the Earth and the moon -- a close shave in the vastness of outer space.

Sudbury said the Cambridge, Massachusetts-based Minor Planet Center, which is affiliated with the Lincoln Lab, had classified the body as a "potentially hazardous asteroid," because of its proximity to Earth which, had it been hit, would have caused a "significant impact."

"Most would just burn up upon entry into the atmosphere," Sudbury said.

"The question, of course, is where the Earth is as the asteroid goes by?"

Sudbury said The Minor Planet Center has several criteria, including size and other factors, to indicate "whether an asteroid could actually penetrate the Earth's atmosphere and do significant damage."

He said scientists were able to reassure the public that there was never any great risk that Monday's asteroid would stray off course and crash into the Earth.

Sudbury told AFP that near-Earth asteroids were once believed to be a rarity, but recent scientific and technological advances have allowed researchers to track asteroids that previously escaped detection.

"In a few years we've detected more than have ever been discovered in history," he said.

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Near Earth asteroid tracking