The 45 m diameter asteroid 2013 SC21 is due to pass the Earth at a distance of 3 382 000 km (8.8 times the average distance at which the Moon orbits the Earth), slightly before 8.45 am GMT on Monday 7 October 2013. The asteroid was first observed on 27 September 2013 by the University of Hawaii's PANSTARRS telescope on Mount Haleakala; the name 2013 SC21 means the 528th object discovered in the second half of September 2013 (Period 2013 S). Although it is on an Earth-orbit crossing trajectory, it 2013 SC21 does not present a significant threat to the Earth; an object this size would be expected to break up in the atmosphere 9-10 km above the ground, with only fragmentary material reaching the surface.
2013 SC21 is calculated to have a 824 day orbital period which brings it at its closest to 0.82 AU from the Sun (i.e. 82% of the average distance at which the Earth orbits the Sun) and which takes it out to 2.6 AU from the Sun, considerably outside the orbit of Mars (which is roughly 1.5 AU from the Sun). This makes it an Apollo Group Asteroid, an asteroid which spends the majority of its time outside the orbit of the Earth but which is closer to the Sun at its perihelion (the point on its orbit when it is closest to the Sun).
See also Asteroid 2013 SU24 to pass the Earth on Saturday 5 October 2013, Asteroid 2013 SK20 passes the Earth, Asteroid 2013 RZ53 passes between the Earth and the Moon, Asteroid 2013 RF74 passes the Earth and Asteroid 2013 RM73 passes the Earth.
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