Asteroid Whizzes Past Earth in a ‘Close Shave’

An asteroid the size of a soccer field narrowly missed the Earth by 75,000 miles--one of the closest known approaches by an object of this size, scientists said Thursday.

“In the unlikely event the asteroid had struck Earth in a populated area, it would have caused considerable loss of life,” said scientist Grant Stokes. “The energy release would be of the magnitude of a large nuclear weapon.”

Stokes is the principal investigator for the MIT-affiliated Lincoln Near Earth Asteroid Research Project, whose New Mexico observatory spotted the object last week.

“It was a close shave,” said another scientist, Brian Marsden of the Harvard-Smithsonian Center for Astrophysics in Cambridge.

Marsden, whose organization gathers information on all such encounters, called it “the only object of this size known to have come closer to the Earth than the moon in decades.”

It was not detected until three days after it came close to the Earth on June 14. When such asteroids are detected, they are usually spotted well out in space when they are approaching or going away from Earth.

The asteroid, provisionally named 2002 MN, was traveling faster than 23,000 mph when it was spotted, Stokes said in a phone interview from Lexington, Mass., where he is associate head of the aerospace division of MIT Lincoln Laboratory.

With a diameter of 50 to 120 yards, the asteroid was about the size of a soccer field, Stokes said. The size of asteroids is estimated by measuring their brightness, without knowing their composition. Damage on the ground depends on what an asteroid is made of, varying from solid metal to a loosely bound aggregate.

There is no dedicated program to search for objects as small as 2002 MN.

“NASA has a goal of discovering and obtaining good orbits for all the near-Earth objects with diameters larger than 1 kilometer [.62 mile],” said Thomas Morgan, a scientist at NASA headquarters in Washington. “Asteroids of this size could potentially destroy civilization as we know it.”

Such asteroids could theoretically hit Earth every million years, or at longer intervals.

Asteroids the size of 2002 MN are estimated to hit the Earth every 100 to several hundred years, causing local damage but no disaster to civilization or the planet’s ecosystem, Stokes said.

“It’s something the public should know about but shouldn’t get nervous about,” he said.