Sunday 19 November 2017

Asteroid 2017 WD passes the Earth.

Asteroid 2017 WD passed by the Earth at a distance of about 715 200 km (1.86 times the average distance between the Earth and the Moon, 0.48% of the distance between the Earth and the Sun), slightly before 11.55 am GMT on Monday 13 November 2017. There was no danger of the asteroid hitting us, though were it to do so it would not have presented a significant threat. 2017 WD has an estimated equivalent diameter of 4-15 m (i.e. it is estimated that a spherical object with the same volume would be 4-15 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 25 km above the ground, with only fragmentary material reaching the Earth's surface.

The calculated orbit of 2017 WD. Minor Planet Center.

2017 WD was discovered on 16 November 2017 (three 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 2017 WD implies that the asteroid was the forth object (object D) discovered in the second half of November 2017 (period 2017 W).  

2017 WD has a 1082 day orbital period and an eccentric orbit tilted at an angle of 3.79° to the plane of the Solar System, which takes it from 0.92 AU from the Sun (i.e. 92% of he average distance at which the Earth orbits the Sun) to 3.20 AU from the Sun (i.e. 320% of the average distance at which the Earth orbits the Sun, slightly more than twice the distance at which the planet Mars orbits). 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).

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