Asteroid 2020 SC passed by the Earth at a distance of about 4910 300 km (1.28 times the average distance between the Earth and the Moon, or 0.33% of the distance between the Earth and the Sun), at about 5.55 pm GMT on Tuesday 15 September 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 SC has an estimated equivalent diameter of 9-29 m (i.e. it is estimated that a spherical object with the same volume would be 9-29 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 33 and 17 km above the ground, with only fragmentary material reaching the Earth's surface.
2020 SC was discovered on 17 September 2020 (two days after its closest approach to the Earth), by he 0.5-m Asteroid Terrestrial-Impact Last Alert System telescope on Mauna Loa in Hawaii. The designation 2020 SC implies that it was the third asteroid (asteroid C - 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 C = 3) discovered in the second half of September 2020 (period 2020 S - the year being split into 24 half-months represented by the letters A-Y, with I being excluded).
2020 SC has a 747 day (2.04 year) orbital period, with an elliptical orbit tilted at an angle of 5.21° to the plain of the Solar System which takes in to 0.52 AU from the Sun (52% of the distance at which the Earth orbits the Sun, and inside the orbit of the planet Venus) and out to 2.70 AU (270% of the distance at which the Earth orbits the Sun, and more than the distance at which the planet 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 is the thought to have been the first close encounter between 2020 SC and the Earth, with two further such encounters predicted in September 2022 and February 2053. The asteroid also had a close encounter with the planet Venus in June 2018.
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