Asteroid 2013 UE3 passed the Earth at a distance of 15 110 000 km (a little under 40 times the distance between the Earth and the Moon) slightly before 9 pm GMT on Sunday 1 December 2013. There was no danger of the asteroid hitting us, though had it done so it would have presented a significant threat. 2013 UE3 is calculated to be between 52 and 160 m in diameter, and an object towards the upper end of this size range would be predicted to be capable of punching straight through the Earth's atmosphere, impacting the ground and resulting in an explosion that would leave a crater over 2 km wide, devastation over a wide area and climatic effects that would be expected to last a number of years.
2013 UE3 was discovered on 24 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 UE3 implies that the asteroid was the 80th object discovered in the second half of October 2013 (period 2013 U).
2013 UE3 has a 379 day orbital period and an eccentric orbit that takes it from 0.79 AU from the Sun (i.e. 79% of the average distance at which the Earth orbits the Sun) to 1.25 AU from the Sun (i.e. 125% of the average distance at which the Earth orbits the Sun, inside the orbit of the planet Mars). 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).
See also Asteroid 2011 JY1 passes the Earth, Asteroid 2013 VX4 passes the Earth, Asteroid 2013 VO4 passes the Earth, Asteroid 1997 WQ23 passes the Earth and Asteroid 2013 VD17 discovered after passing the Earth.
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