Asteroid 2013 XW8 passed by the Earth at a distance of about 7 097 000 km (slightly under 18.5 times the distance between the Earth and the Moon) a little before 7.20 pm GMT on Tuesday 10 December 2013. There was no danger of the asteroid hitting us, and had it done so it would have presented no serious threat. 2013 XW8 is estimated to be between 17 and 54 m in diameter, and an object of this size would be expected to break up in the atmosphere between 25 and 8 km above the Earth's surface, with only fragmentary material reaching the ground.
The calculated orbit of 2013 XW8. JPL Small Body Database Browser.
2013 XW8 was discovered on 6 December 2013 (four days before its closest approach to the Earth) by the University of Hawaii's PANSTARRS telescope on Mount Haleakala. The designation 2013 XW implies that it was the 222nd asteroid discovered in the first half of December 2013 (period 2013 X).
While 2013 XW8 occasionally comes near to the Earth, it does not actually cross our orbital path. It has an elliptical 2.67 year orbit that takes it from 1.004 AU from the Sun (1.004 times the distance at which the Earth orbits the Sun), slightly outside our orbit, to 2.84 AU from the Sun, nearly 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 UC1 passes the Earth, Asteroid 138095 (2000 DK79) passes the Earth, Asteroid 2013 VQ13 discovered after it passes the Earth, Asteroid 2013 UL9 passes the Earth and Asteroid 2013 TY5 passed the Earth.
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