Asteroid 2017 QN2 passed by the Earth at a distance of 216 500 km (0.57 times the average distance between the Earth and the Moon, or 0.14% of the average distance between the Earth and the Sun), slightly before 2.10 am GMT on Sunday 20 August 2017. There was no danger of the asteroid hitting us, though had it done so it would have presented no threat. 2017 QN2 has an estimated equivalent diameter of 4-13 m (i.e. it is estimated that a spherical object with the same volume would be 4-13 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 30 and 45 km above the ground, with only fragmentary material reaching the Earth's surface.
The calculated orbit of 2017 QN2 Minor Planet Center
2017 QN2 was discovered on 18 August 2017 (two days before its closest approach to the Earth) by the University of Hawaii's PANSTARRS telescope on Mount Haleakala on Maui. The designation 2017 QN2 implies that it was the 66th asteroid (asteroid N2) discovered in the second half of August 2017 (period 2017 Q).
2017 QN2 has a 1069 day orbital period and an eccentric orbit tilted at an angle of 3.28° to the plane of the Solar System, which takes it from 0.78 AU from the Sun (i.e. 78% of he average distance at which the Earth orbits the Sun) to 3.31 AU from the Sun (i.e. 331% of the average distance at which the Earth orbits the Sun, and over two times as distant from the Sun as 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). This means that 2017 QN2 has occasional close encounters with the Earth, with the next predicted in July 2020.
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