Asteroid 2020 KU passed by the Earth at a distance of about 387 800 km (1.01 times the average distance between the Earth and the Moon, or 0.26% of the distance between the Earth and the Sun), slightly after 6.20 am GMT on Satuday 23 May 2020. There was no danger of the asteroid hitting us, though were it to do so it would not have presented a significant threat. 2020 KU has an estimated equivalent diameter of 4-12 m (i.e. it is estimated that a spherical object with the same volume would be 4-12 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 30 km above the ground, with only fragmentary material reaching the Earth's surface.
2020 KU was discovered on 17 May 2020 (six days before its closest encounter with the Earth) by the University of Hawaii's PANSTARRS telescope. The designation 2020 KU implies that it was the 20th asteroid (asteroid R - in numbering asteroids the letters A-Y, excluding I, are assigned numbers from 1 to 24, with a number added to the end each time the alphabet is ended, so that A = 1, A1 = 25, A2 = 49, etc., which means that U = 20) discovered in the second half of May 2020 (period 2020 K - the year being split into 24 half-months represented by the letters A-Y, with I being excluded).
2020 KU has an 537 day (1.47 year) orbital period and an eccentric orbit tilted at an angle of 6.64° to the plane of the Solar System, which takes it from 0.95 AU from the Sun (i.e. 95% of the the average distance at which the Earth orbits the Sun) to 1.63 AU from the Sun (i.e. 163% of the average distance at which the Earth orbits the Sun, more than the distance at which 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 fairly common, with the last thought to have happened in October 2017 and the next predicted in October this year (2020). Asteroid 2020 KU also has occasional close encounters with the planet Mars, which it last came close to in December 1973 and is next expected to approach again in February next year (2021).
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