Asteroid 2015 KT154 passed by the Earth at a distance of 15 110 000 km (39.4 times the average distance between the Earth and the Moon, or 1.01% of the average distance between the Earth and the Sun), slightly before 3.00 pm GMT on Wednesday 24 May 2015. There was no danger of the asteroid hitting us, though had it done so it would have presented only a minor threat. 2015 KT154 has an estimated equivalent diameter of 22-68 m (i.e. it is estimated that a spherical object with the same volume would be 22-68 m in diameter), and an object of this size would be expected to explode in an airburst (an explosion caused by superheating from friction with the Earth's atmosphere, which is greater than that caused by simply falling, due to the orbital momentum of the asteroid) in the atmosphere between 20 and 4 km above the ground, with only fragmentary material reaching the Earth's surface. Though since an object at the upper end of this range would explode with the energy equivalent of 15 megatons of TNT (i.e. an explosion roughly 880 times as large as that caused by the Hiroshima bomb), being directly underneath it might be fairly unpleasant.
The calculated orbit of 2015 KT154. JPL Small Body Database.
2015 KT154 was discovered on 26 May 2015 (two days after its closest approach to the Earth) 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 2015 KT154 implies that it was the 3869th asteroid (asteroid T154) discovered in the second half of May 2015 (period 2015 K).
While 2015 KT154 occasionally comes near to the Earth, it does not actually cross our orbital path. It has an elliptical 766 day orbit, at an angle of 23.8° to the plane of the Solar System, that takes it from 1.01 AU from the Sun (1.01 times the average distance at which the Earth orbits the Sun), slightly outside our orbit, to 2.17 AU from the Sun, (2.17 times the distance at which the Earth orbits the Sun and considerably more 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.
See also...
Asteroid 2015 KG passed by the Earth at a distance of 5 510 000 km (14.3 times the average distance between the Earth and the Moon, or 3.68% of the average distance between the Earth and the Sun), slightly before 4.55 am GMT on Monday 18 May 2015...
Asteroid 2015 KM18 passed by the Earth at a distance of 8 760 000 km (22.8 times the average distance between the Earth and the Moon, or 5.86% of the average distance between the Earth and the Sun), slightly before 7.55 am GMT on Sunday 17 May...
Asteroid 2015 JD passed by the Earth at a distance of 1 366 000 km (3.55 times the average distance between the Earth and the Moon, or 9.13% of the average distance between the Earth and the Sun), at about 11.25 pm GMT on Sunday 10 May 2015. There was...
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