Asteroid 2020 SP passed by the Earth at a distance of about 331 800 km (0.86 of the average distance between the Earth and the Moon, or 0.22% of the distance between the Earth and the Sun), slightly before 1.00 am GMT on Sunday 13 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 SP has an estimated equivalent diameter of 7-22 m (i.e. it is estimated that a spherical object with the same volume would be 7-22 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 36 and 20 km above the ground, with only fragmentary material reaching the Earth's surface.
2020 SP was discovered on 17 September 2020 (four days 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 2020 SP implies that the asteroid was the 15th object (asteroid P - 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 P = 15) 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 SP has a 356 day (0.97 year) orbital period, with an elliptical orbit tilted at an angle of 7.13° to the plain of the Solar System which takes in to 0.94 AU from the Sun (94% of the distance at which the Earth orbits the Sun) and out to 1.02 AU (2% further away from the Sun than the Earth). This means that close encounters between the asteroid and Earth are very common, with the last thought to have happened in March this year (2020) and the next predicted in March next year (2021). Although it does cross the Earth's orbit and is briefly further from the Sun on each cycle, 2020 SP spends most of its time closer to the Sun than we are, and is therefore classified as an Aten Group Asteroid.
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