Asteroid 2013 RS43 flew by the Earth at a distance of 1.1 million km (2.9 times as far away as the Moon) on Friday 13 September 2013, making its closest approach at 4.07 pm GMT. The asteroid presented little danger, as at 18 m across it would have been highly unlikely to make it through the Earth's atmosphere intact if it had hit. 2013 RS43 was only discovered a few days before passing the Earth; the name 2013 RS43 means the 1092nd object discovered in the first two weeks of September 2013 (period 2013 R).
2013 RS43 is calculated to have a 643 day orbital period that takes it out beyond the orbit of Mars and brings it slightly within that of the Earth. This means that it will pass the Earth fairly frequently; it is thought to have come within 50.5 km of the Earth in 2004 and is predicted to come within 8.8 million km of us in 2020.
See also The dust tail of 3200 Phaethon, The Perseid Meteors, The perihelion of Comet 103P/Hartley 2, The ejecta of Main-Belt Comet P/2012 T1 (PANSTARRS) and The Main-Belt Comet P/2012 T1 (PANSTARRS).
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