Asteroid 2012 CL19 passed by the Earth at a distance of 14 600 000 km (slightly under 38 times the distance between the Earth and the Moon), a little after 5.15 pm GMT on Friday 20 December 2013. There was no danger of the asteroid hitting us, though were it ever to do so it would present a considerable threat. 2012 CL19 is estimated to be between 82 an 260 m in diameter, and an object towards the upper end of this range would be expected to punch straight through the Earth's atmosphere, impacting the planet's surface, resulting in an explosion around 37 500 times as large as the Hiroshima bomb and creating a crater around 4 km in diameter, as well as devastation over a considerable area and climatic effects that could last for decades.
The calculated orbit of 2012 CL19. JPL Small Body Database Browser.
2012 CL19 was discovered on 11 February 2012 by the University of Arizona's Mt. Lemmon Survey at the Steward Observatory on Mount Lemmon in the Catalina Mountains north of Tucson. The designation 2012 CL19 implies that the asteroid was the 486th object discovered in the first half of February 2012 (period 2012 C).
2012 CL19 has a 713 day orbital period and an eccentric orbit that takes it from 0.87 AU from the Sun (i.e. 87% of the average distance at which the Earth orbits the Sun) to 2.25 AU from the Sun (i.e. 225% 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), and due to its large size and Earth-orbit crossing trajectory it is also considered to be a Potentially Hazardous Asteroid.
See also Asteroid 2013 XG17 passes the Earth, Asteroid 2013 XU21 passes the Earth, Asteroid 2013 WV43 passes the Earth, Asteroid 2013 UE3 passes the Earth and Asteroid 2011 JY1 passes the Earth.
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