Thursday 12 December 2019

Asteroid 2019 XM2 passes the Earth.

Asteroid 2019 XM2 passed by the Earth at a distance of about 879 900 km (2.29 times the average  distance between the Earth and the Moon, or 0.59% of the distance between the Earth and the Sun), slightly after 5.50 pm GMT on Thursday 5 December 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 XM2 has an estimated equivalent diameter of 10-32 m (i.e. it is estimated that a spherical object with the same volume would be 10-32 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 31 and 15 km above the ground, with only fragmentary material reaching the Earth's surface.

 The calculated orbit of 2019 XM2. JPL Small Body Database.

2019 XM2 was discovered on 5 December 2019 (the day of closest encounter with the Earth) by the University of Tokyo's Kiso Observatory. The designation 2019 WM2 implies that the asteroid was the sixtieth 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 M2 = (24 x 2) + 12 = 60) discovered in the first half of December 2019 (period 2019 X).

2019 XM2 has a 479 day orbital period and an eccentric orbit tilted at an angle of 32.8° to the plane of the Solar System, which takes it from 0.96 AU from the Sun (i.e. 96% of he average distance at which the Earth orbits the Sun) to 1.43 AU from the Sun (i.e. 1.43% 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 XM2 occasionally comes close to the Earth, with  the last such lose encounter having happened in June this year (2019) and the next predicted for November 2023.
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