The asteroid 2013 YB passed by the Earth at a distance of 27 290 km (less than 10% of the average distance between the Earth and the Moon, but still more than twice the Earth's diameter), slightly after 12.50 pm on Monday 23 December. While this is a very close approach to the Earth, there was zero danger to anyone on the Earth's surface, as 2013 YB is thought to be less than 3 m in diameter, and an asteroid of this size would be expected to break up in the atmosphere more than 43 km above the planet's surface, making it unlikely that even fragmentary material would reach the ground.
The calculated orbit of 2013 YB. JPL Small Body Database Browser.
2013 YB was discovered on 23 December 2013 (i.e. the day of its closest approach to the Earth) by the University of Arizona's Catalina Sky Survey in the Catalina Mountains north of Tucson. The designation 2013 YB implies that it was the 2nd asteroid discovered in the second half of December 2013 (period 2013 Y).
2013 YB has a 707 day orbital period and an eccentric orbit that takes it from 0.88 AU from the Sun (i.e. 88% of the average distance at which the Earth orbits the Sun) to 2.22 AU from the Sun (i.e. 222% of the average distance at which the Earth orbits the Sun, considerably outside 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 2012 CL19 passes the Earth, Asteroid 2013 XG17 passes the Earth, Asteroid 2013 XU21 passes the Earth, Asteroid 2013 WV43 passes the Earth and Asteroid 2013 UE3 passes the Earth.
Follow Sciency Thoughts on Facebook.