Asteroid 2013 UU1 passed the Earth at a distance of 9 787 000 m (a little under 25.5 times the distance to the Moon) slightly before 0.05 am GMT on 23 October 2013. There was no danger of the asteroid hitting us, though if it had it would have presented a minor risk. 2013 UU1 is estimated to be between 26 and 82 m in diameter, and while an asteroid in this range would be expected to break up in the atmosphere, an object towards the upper end of this range would make it to within one or two kilometers of the planet's surface, creating a massive fireball close to the planet's surface that would cause considerable damage in the immediate area, though it would be unlikely to cause significant global effects.
2013 UU1 was discovered on 23 October 2013 by the University of Hawaii's PANSTARRS telescope on Mount Haleakala. The name 2013 UU1 indicates that it was the 45th such object discovered in the second half of October 2013 (period 2013 U).
While 2013 UU1 occasionally comes near to the Earth, it does not actually cross our orbital path. It has an elliptical 3.72 year orbit that takes it from 1.05 AU from the Sun (1.05 times the distance at which the Earth orbits the Sun), slightly outside our orbit, to 3.75 AU from the Sun, more than twice as far from the Sun as the planet Mars, 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 TK passes the Earth, Asteroid 2013 SB21 passes the Earth, Asteroid 2013 TF 135 passes by the Earth, Asteroid 2010 SG15 passes by the Earth and Asteroid 2013 TQ135 flies past the Earth.
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