Asteroid 2013 XA4 passed the Earth at a distance of 16 810 000 km (approximately 43.75 times the average distance between the Earth and the Moon), slightly before 10.10 am GMT on Sunday 22 December 2013. There was no danger of the asteroid hitting the Earth, though should it do so it would present a considerable threat. 2013 XA4 is estimated to be between 94 an 300 m in diameter, large enough to punch directly through the Earth's atmosphere and impact the planet's surface, resulting in an explosion between 2000 and 70 000 times as powerful as the Hiroshima bomb and creating a crater between 1 and 4.6 km in diameter, as well as devastation over a wide area and climatic effects that could last for decades.
The calculated orbit of 2013 XA4. JPL Small Body Database Browser.
2013 XA4 was discovered on 4 December 2013 by the La Sagra Sky Survey at the Observatorio de La Sagra in Andalucia, Southern Spain. The designation 2013 XA4 implies that it was the 101st asteroid discovered in the first half of December 2013 (period 2013 X).
While 2013 XA4 occasionally comes near to the Earth, it does not actually cross our orbital path. It has an elliptical 4.38 year orbit that takes it from 1.09 AU from the Sun (1.09 times the distance at which the Earth orbits the Sun), slightly outside our orbit, to 4.26 AU from the Sun, (4.26 times the distance at which the Earth orbits the sun and considerably more than twice the distance at which the planet Mars orbits), 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 XY20 passes the Earth, Asteroid 2013 XW8 passes the Earth, Asteroid 2013 UC1 passes the Earth, Asteroid 138095 (2000 DK79) passes the Earth and Asteroid 2013 VQ13 discovered after it passes the Earth.
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