Asteroid 2011 JY1 passed by the Earth at a distance of 2 572 000 km (6.69 times the distance between the Earth and the Moon) slightly after 3.45 am on Thursday 14 November 2013. There was no danger of the asteroid hitting us, and had it done so it would have presented only a very limited danger; 2011 JY1 is calculated to be between 24 and 75 m in diameter, and an object of this size would be expected to break up in the atmosphere between 20 and 3 km above the ground, with only fragmentary material reaching the Earth's surface, though being directly underneath an object towards the upper end of this range would probably be fairly unpleasant.
2011 JY1 was discovere on 3 May 2011 by the the Lincoln Near-Earth Asteroid Research project at the Massachusetts Institute of Technology. The designation 2011 JY1 implies that it was the 49th asteroid discovered in the first half of May 2011 (period 2011 J).
2011 JY1 has a 521 day orbital period and an eccentric orbit that takes it from 0.74 AU from the Sun (i.e. 74% of the average distance at which the Earth orbits the Sun) to 1.79 AU from the Sun (i.e. 179% of the average distance at which the Earth orbits the Sun, 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 2013 VX4 passes the Earth, Asteroid 2013 VO4 passes the Earth, Asteroid 1997 WQ23 passes the Earth, Asteroid 2013 VD17 discovered after passing the Earth and Asteroid 6063 Jason (1984 KB) passes the Earth.
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