Asteroid 2014 HM2 passed by the Earth at a distance of 15 320 000 km (slightly under 40 times the average distance between the Earth and the Moon) a little before 10.10 am on Tuesday 27 May 2014. There was no danger of the asteroid hitting us, though had it done so it would have presented a considerable threat. 2014 HM2 has an estimated equivalent diameter of 78-250 m (that is to say it is estimated that a spherical object with the same volume would have a diameter of 78-250 m), and an object towards the upper end of this range would be capable of passing through the Earth's atmosphere relatively intact, impacting the ground and resulting in an explosion around 43 000 times as large as the Hiroshima bomb. Such an event would leave a crater nearly 4 km across and cause devastation over a much wider area, as well as climatic effects that would last decades.
The calculated orbit of 2014 HM2. JPL Small Body Database Browser.
2014 HM2 was discovered on 20 April 2014 by the University of Arizona's Catalina Sky Survey, which is located in the Catalina Mountains north of Tucson. The designation 2014 HM2 implies that it was the 63rd asteroid (asteroid M2) discovered in the second half of April 2014 (period 2014 H).
While 2014 HM2 occasionally comes near to the Earth, it does not actually cross our orbital path. It has an elliptical 1257 day orbit, that takes it from 1.09 AU from the Sun (1.09 times the distance at which the Earth orbits the Sun), slightly outside our orbit, to 3.47 AU from the Sun, (3.47 times the distance at which the Earth orbits the Sun, and considerably more than 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.
See also...
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