Asteroid 2020 FD passed by the Earth at a distance of about 256 600 km (0.67 times the average distance between the Earth and the Moon, or 0.17% of the distance between the Earth and the Sun), at about 4.05 am GMT on Wednesday 18 March 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 FD has an estimated equivalent diameter of 6-18 m (i.e. it is estimated that a spherical object with the same volume would be 6-18 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 23 km above the ground, with only fragmentary material reaching the Earth's surface.
2020 FD was discovered on 16 March 2020 (two days before its closest encounter with 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 2020 FD implies that the asteroid was the fourth object (asteroid D - 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, so that D = 4) discovered in the second half of March 2020 (period 2020 F).
2020 FD has a 487 day orbital period and an eccentric orbit tilted at an angle of 1.17° to the plane of the Solar System, which takes it from 0.62 AU from the Sun (i.e. 62% of he average distance at which the Earth orbits the Sun, and inside the orbit of the planet Venus) to 1.80 AU from the Sun (i.e. 180% of the average distance at which the Earth orbits the Sun, and 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 fairly common, with the last having occurred in October 2017 and the next predicted in March 2024.
2020 FD also has frequent close encounters with the planets Venus, which it last passed in November 2014 is next predicted to pass in September 2021, and Mars, which it last passed in April 2006 is predicted to pass in September 2024. Asteroids which make close passes to multiple planets are considered to be in unstable orbits, and are often eventually knocked out of these orbits by these encounters, either being knocked onto a new, more stable orbit, dropped into the Sun, knocked out of the Solar System or occasionally colliding with a planet.
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