Thursday 5 May 2016

Asteroid 2016 HD3 passes the Earth.

Asteroid 2016 HD3 passed by the Earth at a distance of 843 000 km (2.19 times the average distance between the Earth and the Moon, or 0.56% of the average distance between the Earth and the Sun), slightly before 6.10 am GMT on Mondya 2 May 2016. There was no danger of the asteroid hitting us, though had it done so it would have presented no threat. 2016 HD3 has an estimated equivalent diameter of 4-15 m (i.e. it is estimated that a spherical object with the same volume would be 4-15  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 42 and 26 km above the ground, with only fragmentary material reaching the Earth's surface.
 
 The calculated orbit of  2016 HD3JPL Small Body Database.
 
2016 HD3 was discovered on 27 April 2016 (five days 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 2016 HD3 implies that the asteroid was the 79th object (object D3) discovered in the second half of April 2016 (period 2016 H).
 
2016 HD3  has a 322 day orbital period, with an elliptical orbit tilted at an angle of 0.63° to the plain of the Solar System which takes in to 0.70 AU from the Sun (70% of the distance at which the Earth orbits the Sun and approximately the orbit of the planet Venus) and out to 1.14 AU (14% further away from the Sun than the Earth). This means that close encounters between the asteroid and Earth are fairly common, with the last thought to have happened in September 2015 and the next predicted in November 2022. 2016 HD3 also has frequent close encounters with the planet Venus, with the last thought to have occurred in April 2011 and the next predicted for July 2023. Although it does cross the Earth's orbit and is briefly further from the Sun on each cycle, 2016 HD3 spends most of its time closer to the Sun than we are, and is therefore classified as an Aten Group Asteroid. 
 
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