Tuesday 28 March 2017

Asteroid 2017 FJ passes the Earth.

Asteroid 2017 FJ passed by the Earth at a distance of 762 600 km (1.98 times the average distance between the Earth and the Moon, 0.51% of the average distance between the Earth and the Sun), slightly after 3.00 pm GMT on Tuesday 21 March 2017. There was no danger of the asteroid hitting us, though had it done so it would have presented no threat. 2017 FJ 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 27 km above the ground, with only fragmentary material reaching the Earth's surface.
The calculated orbit of 2017 FJ. Minor Planet Center.

2017 FJ was discovered on 17 March 2017 (four 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 2017 FJ implies that the asteroid was the ninth object (object J) discovered in the second half of March 2017 (period 2017 F).

2017 FJ has a 721 day orbital period and an eccentric orbit tilted at an angle of 3.43° to the plane of the Solar System, which takes it from 0.92 AU from the Sun (i.e. 92% of he average distance at which the Earth orbits the Sun) to 2.23 AU from the Sun (i.e. 2.23% of the average distance at which the Earth orbits the Sun, considerably outside the orbit of 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 May 2015 and the next predicted in February 2019.  

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