The asteroid 2013 XG17 passed by the Earth at a distance of 9 116 000 km (slightly under 24 times the distance between the Earth and the Moon), a little before 4.55 am GMT on Tuesday 17 December 2013. There was no danger of the asteroid hitting us, though were it to do so it would present a credible threat. 2013 XG17 is estimated to be between 52 and 160 m in diameter, and an object towards the upper end of this range would be capable of punching directly through the Earth's atmosphere and impacting the ground, creating a crater around 2.5 km in diameter, as well as causing devastation over a wide year and climatic effects that would probably last for years.
The calculated orbit of 2013 XG17. JPL Small Body Database Browser.
2013 XG17 was discovered on 10 December 2013 (i.e. seven days before 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 XG17 implies that it was the 432nd asteroid discovered in the first half of December 2013 (period 2013 X).
2013 XG17 has a 4.07 year orbital period and an eliptical orbit tilted to the plane of the Solar System that takes it from 0.67 AU from the Sun (i.e. 67% of the distance between the Earth and the Sun, inside the orbit of the planet Venus) to 4.43 AU from the Sun (i.e. 443% of the average distance at which the Earth orbits the Sun, considerably more than twice the distance at which Mars orbits 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).
Having passed by the Earth this month, 2013 XG17 is expected to make a close pass of the planet Venus on 7 January 2014, missing the planet by approximately 20 390 000 km.
See also Asteroid 2013 XU21 passes the Earth, Asteroid 3023 WV43 passes the Earth, Asteroid 2013 UE3 passes the Earth, Asteroid 2011 JY1 passes the Earth and Asteroid 2013 VX4 passes the Earth.
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