Saturday 7 January 2017

Asteroid 2017 AP4 passes the Earth.

Asteroid 2017 AP4 passed by the Earth at a distance of 859 900 km (2.24 times the average distance between the Earth and the Moon, 0.57% of the average distance between the Earth and the Sun), slightly before 1.200 am GMT on Sunday 1 January 2017. There was no danger of the asteroid hitting us, though had it done so it would have presented no threat. 2017 AP4 has an estimated equivalent diameter of 7-25 m (i.e. it is estimated that a spherical object with the same volume would be 7-25 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 37 and 20 km above the ground, with only fragmentary material reaching the Earth's surface. 
 The calculated orbit of 2017 AP4. Minor Planet Center.
2017 AP4 was discovered on 4 January 2017 (three days after its closest approach to the Earth) by the University of Hawaii's PANSTARRS telescope on Mount Haleakala on Maui. The designation 2017 AP4 implies that it was the 115th asteroid (asteroid P4) discovered in the first half of January 2017 (2017 A).
2017 AP4 has a 1096 day orbital period and an eccentric orbit tilted at an angle of 1.45° to the plane of the Solar System, which takes it from 0.97 AU from the Sun (i.e. 97% of the average distance at which the Earth orbits the Sun) to 3.19 AU from the Sun (i.e. 319% of the average distance at which the Earth orbits the Sun, and more than twice the distance at which the planet Mars orbits). 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).  
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