Monday 12 December 2016

Asteroid 2016 XE passes the Earth.

Asteroid 2016 XE passed by the Earth at a distance of 566 800 km (1.47 times the average distance between the Earth and the Moon, 0.38% of the average distance between the Earth and the Sun), slightly after 8.40 am GMT on Wednesday 7 December 2016. There was no danger of the asteroid hitting us, though had it done so it would have presented no threat. 2016 XE has an estimated equivalent diameter of 4-14 m (i.e. it is estimated that a spherical object with the same volume would be 4-14 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 43 and 28 km above the ground, with only fragmentary material reaching the Earth's surface. 

The calculated orbit of 2016 XE. Minor Planet Center.

2016 XE was discovered on 1 December 2016 (six days before 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 2016 XE implies that the asteroid was the fifth object (object XE) discovered in the first half of December 2016 (period 2016 X).

2016 XE is calculated to have a 398 day orbital period and an elliptical orbit tilted at an angle of 0.97° to the plain of the Solar System that takes it from 0.80 AU from the Sun (i.e. 80% of the average distance at which the Earth orbits the Sun) to 1.31 AU from the Sun (i.e. 131% of the average distance at which the Earth orbits the Sun). 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 close encounters between the asteroid and Earth are extremely common, with the last having occurred in November 2015 and the next predicted in September 2017. 2016 XE  also has frequent close encounters with the planet Mars, with the last calculated to have happened in June 1975 next predicted for September 2018.   

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