Asteroid 1999 SH10 passed by the Earth at a distance of 17 160 000 km (almost 45 times the average distance between the Earth and the Moon), slightly before 6.40 pm GMT on Friday 18 April 2014. There was no danger of the asteroid hitting us, though if it were to do so it would present a considerable hazard. 1999 SH10 is estimated to be between 57 m and 180 m in diameter, and an object towards the upper end of this range would be expected to be capable of punching straight through the Earth's atmosphere, impacting the ground directly in an explosion around 60 000 times as large as the one caused by the Hiroshima bomb, and creating a crater over 2.5 km wide. Such an event would cause devastation over a wide area, and climatic effects that would probably last for decades.
1999 SH10 was discovered on 30 September 1999 by the Lincoln Near-Earth Asteroid Research (LINEAR) project in New Mexico. The designation 1999 SH10 implies that it was the 258th object (object H10) discovered in the second half of September 1999 (period 1999 S).
1999 SH10 has a 420 day orbital period and an eccentric orbit tilted to the plane of the Solar System that takes it from 0.95 AU from the Sun (i.e. 95% of the average distance at which the Earth orbits the Sun) to 1.24 AU from the Sun (i.e. 124% of the average distance at which the Earth orbits the Sun). It is therefore classed as an Apollo Group Asteroid (an asteroid that is on average further from the Sun than the Earth, but which does get closer).
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