Asteroid 2013 UR4 passed the Earth at a distance of about 18 010 000 km (slightly over 47 times the distance between the Earth and the Moon) at about 9.05 pm GMT on Monday 28 October 2013. There was no danger of the asteroid hitting us, and if it had it would have presented only a limited danger. 2013 UR4 is estimated to be between 22 and 68 m in diameter, and such an object would be expected to break up in the atmosphere at an altitude of between 22 and 3.5 km, with only fragmentary material reaching the planets surface; potentially unpleasant for anyone directly underneath, but not likely to cause damage beyond a limited area.
2013 UR4 was discovered on 25 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 UR4 implies that the asteroid was the 117th object discovered in the second half of October 2013 (period 2013 U).
While 2013 UR4 occasionally comes near to the Earth, it does not actually cross our orbital path. It has an elliptical 3.50 year orbit that takes it from 1.11 AU from the Sun (1.11 times the distance at which the Earth orbits the Sun), slightly outside our orbit, to 3.5 AU from the Sun, more than twice the distance at which the planet Mars orbits the Sun; so unless an encounter with another body causes it's orbital path to alter in a very specific way (highly unlikely) there is no chance of it hitting the Earth. As a Near Earth Object that remains strictly outside the orbit of the Earth it is classed as an Amor Family Asteroid.
See also Asteroid 2013 TY5 passed the Earth, Asteroid 2013 UU4 passes the Earth, Asteroid 2013 UQ1 passes the Earth, Asteroid 2013 TO69 passed the Earth and Asteroid 2012 ER14 flies by the Earth.
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