Friday, 22 November 2019

Asteroid 2019 WD passes the Earth.

Asteroid 2019 WD passed by the Earth at a distance of about 652 500 km (2.48 times the average  distance between the Earth and the Moon, or 0.64% of the distance between the Earth and the Sun), slightly before 9.00 pm GMT on Friday 15 November 2019. There was no danger of the asteroid hitting us, though were it to do so it would not have presented a significant threat. 2019 WD has an estimated equivalent diameter of 11-35 m (i.e. it is estimated that a spherical object with the same volume would be 11-35 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 12 km above the ground, with only fragmentary material reaching the Earth's surface.

 The calculated orbit of 2019 WD. JPL Small Body Database.

2019 WD was discovered on 17 November 2019 (two days after its closest encounter with 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 2019 WD implies that the asteroid was the fourth object (asteroid D - in numbering asteroids the letters A-Y, excluding I, are assigned numbers from 1 to 24, with a number added to the end each time the alphabet is ended, so that A = 1, A1 = 25, A2 = 49, etc., which means that D = 4) discovered in the second half of November 2019 (period 2019 W).

2019 WD has a 1280 day orbital period and an eccentric orbit tilted at an angle of 1.38° to the plane of the Solar System, which takes it from 0.97 AU from the Sun (i.e. 97% of he average distance at which the Earth orbits the Sun) to 3.64 AU from the Sun (i.e. 364% 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 2019 WD occasionally comes close to the Earth, with  next such encounter predicted for December 2026.

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