Asteroid 2013 UB passed by the Earth at a distance of 618 900 km (1.6 times the distance to the Moon), slightly after 9.50 am on Saturday 19 October 2013. There was no risk of the asteroid hitting us, and even if it had it would have presented no serious risk; 2013 UB is estimated to be between 9 and 28 m in diameter, and an object this size would be expected to break up in the atmosphere between 16 and 32 km above the ground, with only fragmentary material reaching the Earth's surface.
2013 UB was discovered on 16 October 2013 by the University of Arizona's Mt. Lemmon Survey at the Steward Observatory on Mount Lemmon in the Catalina Mountains north of Tucson. The designation 2013 UB implies that the asteroid was the second object discovered in the second half of October 2013 (period 2013U).
2013 UB has a 285 day orbital period, with an elliptical orbit that briefly takes it further from the Sun than Earth for a short period on each circuit. This means that close encounters between the asteroid and Earth are fairly common, with the last thought to have happened in May 2007 and the next predicted in August 2016. Although 2013 does cross the Earth's orbit and is briefly further from the Sun on each cycle, 2013 UB spends most of its time closer to the Sun than we are, and is therefore classified as an Aten Group Asteroid.
See also Asteroid 2013 TN127 flies past the Earth, Asteroid 2013 TB6 to pass by the Earth on Wednesday 9 October 2013 and Asteroid 2013 SM20 to pass the Earth on Tuesday 8 October 2013.
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