A gigantic asteroid zipped past the Earth without incident on Tuesday, the U.S. space agency NASA said, revealing surprising details about the celestial visitor.

NASA scientists revealed on Monday that a tiny moon is orbiting asteroid 2004 BL86 and it has a brief "day" - completing a rotation once about every two and a half hours.

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The space agency earlier estimated the size of the asteroid to be around 500 meters in width based on its brightness. Based on new radar data, scientists changed their estimate to 300 meters, which is about the length of six Olympic size swimming pools.

Sky gazers found the asteroid in 2004 and it is expected not to fly this close to Earth for another 200 years, NASA said.

New radar images of the asteroid also show what appear to be boulders. NASA researcher Lance Benner broadcast the images live over the Internet during the asteroid's nearest approach to Earth on Monday morning.

At its nearest approach, the space debris was around one and one-fifths million kilometers from the Earth, which is three times the distance of the moon from our planet's surface.

Scientists said the asteroid was far enough for comfort, but the nearest any other space rock this huge will come near the planet is in 2027 when asteroid 1999 AN10 comes for a visit.

NASA has been keeping a close watch on the asteroid, recording radar data and pictures through its Goldstone Deep Space Network antenna in California. NASA's Arecibo Observatory in Puerto Rico will also track the space rock over the next few days.

Check it out in this video posted by Dr. Fritz Helmut Hemmerich on You Tube:

TagsNASA, Asteroid flyby, 2004 BL86, moon