Asteroid 2020 SO1 passed by the Earth at a distance of about 432 800 km (1.13 times the average distance between the Earth and the Moon, or 0.29% of the distance between the Earth and the Sun), slightly before 10.35 am GMT on Wednesday 16 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 SO1 has an estimated equivalent diameter of 7-23 m (i.e. it is estimated that a spherical object with the same volume would be 7-23 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 37 and 20 km above the ground, with only fragmentary material reaching the Earth's surface.
2020 SO1 was discovered on 19 September 2020 (three days after 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 2020 SO1 implies that it was the 38th asteroid (object O1 - 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 O1 implies the 38th asteroid (N2 = (24 x 1) + 14 = 38)) 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 SO1 has a 623 day (1.71 year) orbital period, with an elliptical orbit tilted at an angle of 1.60° to the plain of the Solar System which takes in to 1.01 AU from the Sun (101% of the distance at which the Earth orbits the Sun) and out to 1.84 AU (309% of the distance at which the Earth orbits the sun and further from the Sun as the planet Mars). This means that close encounters between the asteroid and Earth happen occasionally, with the last calculated to have happened in October 2008 next predicted in July 2027. 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). 2020 SO1 also has occassional close encounters with the planet Mars, with the last having happened in September 1983, and the next predicted for December 2041.
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