The 780 - 1800 metre wide asteroid 1998 ST49 will make a close pass (28.7 lunar distances, 0.0737 au), travelling at 16.63 km/second, to the Earth-Moon system on the 18th October, 2012 @ 05:38 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).