The 180 - 390 metre wide asteroid 2003 YX1 will make a close pass (64.4 lunar distances, 0.1654 AU), travelling at 11.76 km/second, to the Earth-Moon system on the 21st March 2014 @ 05:30 UT ±00:01.
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The Lunar Distance (LD), the distance between Earth and the Moon, equals 384,401 km, (or 0.00256 AU).