Asteroid 2019 FC1 passed by the Earth at a distance of about 103 200 km (0.27 times the average distance between the Earth and the Moon, or 0.07% of the distance between the Earth and the Sun), slightly after 5.45 am GMT on Thursday 28 March 2019. There was no danger of the asteroid hitting us, though were it to do so it would not have presented a significant threat. 2019 FC1 has an estimated equivalent diameter of 14-45 m (i.e. it is estimated that a spherical object with the same volume would be 14-45 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.
2019 FC1 was discovered on 29 March 2019 (the day after 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 2019 FC1 implies that the asteroid was the 27th object (object C1 - in numbering asteroids the letters A-Y, excluding I, are assigned numbers from 1 to 24, so that M5 = (24 x 1) + 3 = 27) discovered in the second half of March 2019 (period 2019 F).
2019 FC1 has an 1202 day orbital period and an eccentric orbit tilted at an angle of 1.98° to the plane of the Solar System, which takes it from 0.43 AU from the Sun (i.e. 43% of the the average distance at which the Earth orbits the Sun, and slightly outside the orbit of Mercury) to 3.99 AU from the Sun (i.e. 399% of the average distance at which the Earth orbits the Sun, and somewhat more than twice the distance at which Mars orbits). 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 common, with the last having occurred in October 1981 and the next predicted in October 2071.
2019 FC1 also has frequent close encounters with the planets Venus, which it last came close to in November 1984 and is next predicted to pass in December 2071, Mars, which it last passed in October 1984 and Jupiter, which it last came close to in October 1983 and is next predicted to pass in January 2067. 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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