Tuesday 17 December 2019

Asteroid 2019 XN passes the Earth.

Asteroid 2019 XN passed by the Earth at a distance of about 931 000 km (2.43 times the average  distance between the Earth and the Moon, or 0.62% of the distance between the Earth and the Sun), at about 11.45 am GMT on Friday 6 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 XN has an estimated equivalent diameter of 5-17 m (i.e. it is estimated that a spherical object with the same volume would be 5-17 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 40 and 25 km above the ground, with only fragmentary material reaching the Earth's surface.

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

2019 XN was discovered on 3 December 2019 (four days before 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 XN implies that the asteroid was the thirteenth object (asteroid N - 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 N = 13) discovered in the first half of December 2019 (period 2019 X).

2019 XN has a 1458 day orbital period and an eccentric orbit tilted at an angle of 0.39° to the plane of the Solar System, which takes it from 0.95 AU from the Sun (i.e. 95% of he average distance at which the Earth orbits the Sun) to 4.08 AU from the Sun (i.e. 408% of the average distance at which the Earth orbits the Sun, more than twice as distant from the Sun as the planet Mars). 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 XN occasionally comes close to the Earth, with  the  such encounter having happened in January 2008 and the next predicted for October 2023. 2019 XN also has occasional close encounters with the planet Mars, with the last having occurred in November 2003.

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