A large asteroid accompanied by its own small moon came within 3.6 million miles of Earth on Friday, the latest in a string of celestial visitors drawing attention to the potential dangers of objects in space.
The asteroid is roughly 15 times farther away than the Earth's moon.
Asteroid 1998 QE2 - which is not named for the United Kingdom's monarch - is about 1.7 miles in diameter, about nine times as long as the Queen Elizabeth II ocean liner.
It is far bigger than the small asteroid that blasted through the skies over Chelyabinsk, Russia, on February 15, leaving more than 1,500 people injured by flying glass and debris.
That same day another asteroid, about 150 feet in diameter, passed about 17,200 miles from Earth - closer than the networks of communication satellites that ring the planet.
"For an asteroid of this size, it's a close shave," said Paul Chodas, a scientist with NASA's Near Earth Object program office at the Jet Propulsion Laboratory in Pasadena, California.
NASA is tracking 95 percent of the large asteroids with orbits that come relatively close to Earth. The U.S. space agency, as well as Russia, Europe, and others, plans to beef up asteroid detection efforts to find smaller objects that could still do considerable damage if they hit a populated area.
Scientists used radar to get a preview of the asteroid on Wednesday and discovered it had a small moon in tow.
"It was quite a surprise," Marina Brozovic, a radar scientist with the Jet Propulsion Laboratory, said in a NASA TV interview.
After its pass around the sun, QE2 will head back toward the outer asteroid belt on an orbit that extends nearly to Jupiter.
Friday's flyby is the closest QE2 will come to Earth for at least the next 200 years, Chodas said.
Astronomers are hoping to get images and data during the flyby that will be as good as what spacecraft visiting other asteroids have returned.
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