Sunday 4 December 2016

Asteroid 2016 WG7 passes the Earth.

Asteroid 2016 WG7 passed by the Earth at a distance of 1 002 000 km (2.61 times the average distance between the Earth and the Moon, 0.67% of the average distance between the Earth and the Sun), at about 3.55 pm GMT on Thursday 1 December 2016. There was no danger of the asteroid hitting us, though had it done so it would have presented no threat. 2016 WG7 has an estimated equivalent diameter of 12-38 m (i.e. it is estimated that a spherical object with the same volume would be 12-38 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 10 km above the ground, with only fragmentary material reaching the Earth's surface. 

The calculated orbit of 2016 WG7. Minor Planet Center.

2016 WG7 was discovered on 25 November 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 WG7 implies that the asteroid was the 182nd object (object G7) discovered in the second half of November 2016 (period 2016 W).
2016 WG7 has a 340 day orbital period, with an elliptical orbit tilted at an angle of 4.53° to the plain of the Solar System which takes in to 0.75 AU from the Sun (75% of the distance at which the Earth orbits the Sun; slightly outside the orbit of the planet Venus) and out to 1.16 AU (16% further away from the Sun than the Earth). This means that close encounters between the asteroid and Earth are fairly common, with the last thought to have happened in March this year and the next predicted in November 2017. 2016 WG7  also has frequent close encounters with the planet Venus, with the next predicted forJuly 2024. Although it does cross the Earth's orbit and is briefly further from the Sun on each cycle, 2016 WG7 spends most of its time closer to the Sun than we are, and is therefore classified as an Aten Group Asteroid.
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