Friday 14 December 2018

Asteroid 2018 XP2 passes the Earth.

Asteroid 2018 XP2 passed by the Earth at a distance of about 388 000 km (1.01 times the average distance between the Earth and the Moon, or 0.02% of the distance between the Earth and the Sun), at about 9.50 pm GMT on Saturday 8 December 2018. There was no danger of the asteroid hitting us, though were it to do so it would not have presented a significant threat. 2018 XP2 has an estimated equivalent diameter of 4-14 m (i.e. it is estimated that a spherical object with the same volume would be 4-14 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 28 km above the ground, with only fragmentary material reaching the Earth's surface.

 The calculated orbit of 2018 XP2. Minor Planet Center.

2018 XP2 was discovered on 10 December 2018 (two 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 2018 XP2 implies that the asteroid was the 65th object (object P2) discovered in the first half of December 2018 (period 2018 X).

2018 XP2 has an 890 day orbital period and an eccentric orbit tilted at an angle of 66.3° to the plane of the Solar System, which takes it from 0.43 AU from the Sun (i.e. 43% of he average distance at which the Earth orbits the Sun and slightly outside the orbit of the planet Mercury) to 3.19 AU from the Sun (i.e. 3.19% of the average distance at which the Earth orbits the Sun, ,ore than twice far 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). As such the asteroid has occasional close encounters with the planet Earth, which it is expected to pass again in May 2072. The asteroid also has occasional close encounters with the planet Mars, which it last came close to in February 2016 and is next predicted to pass in August 2077.
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