Asteroid 2018 FK5 passed by the Earth at a distance of about 150 200 km (0.39 times the average distance between the Earth and the Moon, or 0.10% of the distance between the Earth and the Sun), slightly before 1.30 pm GMT on Friday 30 March 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 FK5 has an estimated equivalent diameter of 4-13 m (i.e. it is estimated that a spherical object with the same volume would be 4-13 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 28 km above the ground, with only fragmentary material reaching the Earth's surface.
2018 FK5 was discovered on 28 March 2018 (two 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 2018 FK5 implies that the asteroid was the 235th object (object K5) discovered in the second half of March 2018 (period 2018 F).
2018 FK5 has a 400 day orbital period and an eccentric orbit tilted at an angle of 12.1° to the plane of the Solar System, which takes it from 0.74 AU from the Sun (i.e. 74% of he average distance at which the Earth orbits the Sun, slightly outside the orbit of the planet Venus) to 1.38 AU from the Sun (i.e. 138% of the average distance at which the Earth 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 the asteroid has occasional close encounters with the Earth, with the last thought to have happened in October 2008 and the next predicted in October 2019. The asteroid also has occasional close encounters with the planet Venus, with the last thought to have happened in December 2011.
Follow Sciency Thoughts on Facebook.