Asteroid 2014 YM9 passed by the Earth at a distance of 15 510 000 km (40.35 times the average distance between the Earth and the Moon, or 10.4 % of the average distance between the Earth and the Sun), slightly after 11.10 pm GMT on Thursday 12 February 2015. There was no danger of the asteroid hitting us, though had it done so it would have presented a considerable threat. 2014 YM9 has an estimated equivalent diameter of 270-860 m (i.e. it is estimated that a spherical object with the same volume would be 270-860 m in diameter), and an object of this size would pass through the atmosphere and directly impact the ground with a force of about 800-25 000 megatons (about 47 000-1 470 000 times the explosive energy of the Hiroshima bomb), causing devastation over a wide area and creating a crater 4-12 kilometers across, and resulting in global climatic problems that could last for decades or even centuries.
The calculated orbit of 2014 YM9. JPL Small Body Database.
2014 YM9 was discovered on 20 December 2014 by the University of Hawaii's PANSTARRS telescope on Mount Haleakala on Maui. The designation 2014 YM9 implies that it was the 237th asteroid (asteroid M9) discovered in the second half of December 2014 (period 2014 Y).
While 2014 YM9 occasionally comes near to the Earth, it does not actually cross our orbital path. It has an elliptical 959 day orbit, at an angle of 19.7° 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 2.76 AU from the Sun, (2.76 times the distance at which the Earth orbits the Sun, almost twice 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 orbit also means that close encounters between 2014 YM9 and the Earth are extremely common, with the last having occured in February 1994 and the next predicted for February 2036.
See also...
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