Sunday 29 April 2018

Asteroid 2018 HV passes the Earth.

Asteroid 2018 HV passed by the Earth at a distance of about 154 800 km (0.40 times the average  distance between the Earth and the Moon, or 0.10% of the distance between the Earth and the Sun), slightly after 5.05 pm GMT on Sunday 22 April 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 HV has an estimated equivalent diameter of 3-9 m (i.e. it is estimated that a spherical object with the same volume would be 3-9 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 50 and 33 km above the ground, with only fragmentary material reaching the Earth's surface.

The calculated orbit of 2018 HV. Minor Planet Center.

2018 HM was discovered on 21 April 2018 (the day 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 2018 HV implies that the asteroid was the 21st object (object V) discovered in the second half of April 2018 (period 2018 H).   

2018 HV has a 514 day orbital period and an eccentric orbit tilted at an angle of 10.3° to the plane of the Solar System, which takes it from 0.65 AU from the Sun (i.e. 65% of he average distance at which the Earth orbits the Sun, slightly inside the orbit of the planet Venus) to 1.86 AU from the Sun (i.e. 186% of the average distance at which the Earth orbits the Sun, and more 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 close encounters between the asteroid and Earth are common, with the last having occurred in October 2015 and the next predicted in April 2022. 2018 also has occasional close encounters with the planet Venus, with the last having occurred in December 2009 and the next predicted for April 2021.

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