The Asteroid 2013 UK9 passed the Earth at a distance of 4 089 000 km (a little over 10.6 times as distant as the Moon) slightly before 2.00 pm GMT on Friday 25 October 2013. There was no danger of the asteroid hitting us, and even if it had done so it would have presented little danger. 2013 UK9 has an estimated diameter of 12-38 m, and an object of this size would be expected to break up in the Earth's atmosphere at an altitude of between 30 and 12 km above the ground, with only fragmentary material reaching the Earth's surface.
2013 UK9 was discovered on 30 October 2013 by the University of Arizona's Catalina Sky Survey in the Catalina Mountains north of Tucson. The designation 2013 UK9 implies that it was the 235th such object discovered in the second half of October 2013 (period 2013 U).
2013 UK9 has a 966 day (2.65 year) orbital period and an eliptical orbit that takes it from 0.97 AU from the Sun (i.e. 97% of the average distance at which the Earth orbits the Sun, slightly inside the orbit of the Earth) to 2.85 AU from the Sun (i.e. 285% of the average distance at which the Earth orbits the Sun, and nearly twice as far as Mars is from 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).
See also Asteroid 2013 UR1 flies between the Earth and the Moon, Asteroid 2013 UT3 passes by the Earth, Asteroid 2013 SL20 passes the Earth, Asteroid 2013 TX68 passes the Earth and Asteroid 2013 TT5 passes by the Earth.
Follow Sciency Thoughts on Facebook.