Asteroid 2018 KF1 passed by the Earth at a distance of about 861 400 km (2.24 times the average distance between the Earth and the Moon, or 0.58% of the distance between the Earth and the Sun), slightly after midnight GMT on Monday 21 May 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 KF1 has an estimated equivalent diameter of 13-41 m (i.e. it is estimated that a spherical object with the same volume would be 13-41 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 28 and 10 km above the ground, with only fragmentary material reaching the Earth's surface.
2018 KF1 was discovered on 19 May 2018 (two days before its closest approach to the Earth) by the University of Arizona's Catalina Sky Survey, which is located in the Catalina Mountains north of Tucson. The designation 2018 KF1 implies that it was the 31st asteroid (asteroid F1) discovered in the second half of May 2018 (period 2018 K).
2018 KF1 has a 1284 day orbital period and an eccentric orbit tilted at an angle of 6.01° to the plane of the Solar System, which takes it from 1.01 AU from the Sun (i.e. 101% of he average distance at which the Earth orbits the Sun) to 3.61 AU from the Sun (i.e. 361% of the average distance at which the Earth orbits the Sun, and more than twice as far from the Sun as the planet Mars). It is therefore classed as an Amor Group Asteroid (an asteroid which comes close to the Earth, but which is never closer to the Sun than the Earth is). This means that the asteroid has occasional close encounters with the Earth, with the last thought to have happened in April 2011 and the next predicted in April 2025. The asteroid also has occasional close encounters with the planet Jupiter, with the last thought to have happened in February 2013.
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