Asteroid 2011 YC29 passed by the Earth at a distance of 9 438 000 km (24.5 times the average distance between the Earth and the Moon, or 6.31% of the average distance between the Earth and the Sun), at about 10.10 am GMT on Wednesday 15 July 2015. There was no danger of the asteroid hitting us, though had it done so it would have presented a considerable threat. 2011 YC29 has an estimated equivalent diameter of 71-230 m (i.e. a spherical body with the same mass would be 71-230 m in diameter, and an object towards the upper end of this range would pass through the atmosphere and directly impact the ground with a force of about 400 megatons (about 23 500 times the explosive energy of the Hiroshima bomb), causing devastation over a wide area and creating a crater over 3.5 kilometers across, and resulting in global climatic problems that could last for decades or even centuries.
The calculated orbit of 2011 YC29. JPL Small Body Database.
2011 YC29 was discovered on 29 December 2011 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 2011 YC29 implies that it was the 728th asteroid (asteroid C29) discovered in the second half of December 2011 (period 2011Y).
While 2011 YC29 occasionally comes near to the Earth, it does not actually cross our orbital path. It has an elliptical 498 day orbit, at an angle of 23.1° to the plane of the Solar System, that takes it from 1.04 AU from the Sun (1.04 times the average distance at which the Earth orbits the Sun), slightly outside our orbit, to 1.42 AU from the Sun, (1.42 times the distance at which the Earth orbits the Sun and slightly less than the distance at which the planet Mars orbits the Sun). As a Near Earth Object that remains strictly outside the orbit of the Earth it is classed as an Amor Family Asteroid. This means that close encounters between the asteroid and Earth are extremely common, with the last having occurred in January 2012 and the next predicted in December this year.
See also...
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