The 9 - 21 metre wide asteroid 2013 XT21 made a close pass (1.1 lunar distances, 0.0029 AU), travelling at 13.55 km/second, to the Earth-Moon system on the 11th December, 2013 @ 23:50 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).
