An asteroid the size of a mountain will fly relatively close by Earth on Monday, in a rare type of encounter that will not be seen for another decade, astronomers said Monday. The asteroid, called 2004 BL86, poses no risk of hitting Earth and will be about three times farther away than the moon when it passes. At the time of its closest approach, the asteroid will be about 1.2 million kilometers from Earth. The asteroid is unusual because of its large size of about 0.5 kilometers across. The majority of near-Earth objects are 15 to 30 meters in diameter. "It's the largest known space rock predicted to come this close to us until 2027," said Sky and Telescope magazine. Meanwhile, astronomers are excited for the chance to view 2004 BL86, a mysterious asteroid that will not pass by again for about 200 years. "At present, we know almost nothing about the asteroid, so there are bound to be surprises," said radar astronomer Lance Benner of the National Aeronautics and Space Administration's (NASA's) Jet Propulsion Laboratory. "When we get our radar data back the day after the flyby, we will have the first detailed images."
