Thursday 23 March 2017

Asteroid 2017 FD3 passes the Earth.

Asteroid 2017 FD3 passed by the Earth at a distance of 180 000 km (0.47 times the average distance between the Earth and the Moon, 0.12% of the average distance between the Earth and the Sun), slightly before 2.30 pm GMT on Friday 17 March 2017. There was no danger of the asteroid hitting us, though had it done so it would have presented no threat. 2017 FD3 has an estimated equivalent diameter of 5-17 m (i.e. it is estimated that a spherical object with the same volume would be 5-17 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 40 and 25 km above the ground, with only fragmentary material reaching the Earth's surface.

The calculated orbit of 2017 FD3. Minor Planet Center.

2017 FD3 was discovered on 19 March 2017 (two days after its closest encounter with the Earth) by the University of Arizona's Catalina Sky Survey, which is located in the Catalina Mountains north of Tucson. The designation 2017 FD3 implies that it was the 79th asteroid (asteroid D3) discovered in the second half of March 2017 (period 2017 F).
2017 FD3 is calculated to have a 1008 day orbital period and an elliptical orbit tilted at an angle of 2.12° to the plain of the Solar System that takes it from 0.87 AU from the Sun (i.e. 87% of the average distance at which the Earth orbits the Sun) to 3.05 AU from the Sun (i.e. 305% of the average distance at which the Earth orbits the Sun, more than twice the distance at which the planet Mars orbits the Sun). 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 extremely common, with the last having occurred in November 1969 and the next predicted in November 2019. 2017 FD3  also has frequent close encounters with the planet Mars, with the next predicted for April 2080.
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