Asteroid 2020 YM1 passed by the Earth at a distance of about 634 400 km (1.65 times the average distance between the Earth and the Moon, or 0.42% of the distance between the Earth and the Sun), slightly before 0.55 am GMT on Friday 25 December 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 YM1 has an estimated equivalent diameter of 2-7 m (i.e. it is estimated that a spherical object with the same volume would be 2-7 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) more than 36 km above the ground, with only fragmentary material reaching the Earth's surface.
2020 YM1 was discovered on 19 December 2020 (six days before 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 YM1 implies that the asteroid was the 37th object (asteroid M1 - in numbering asteroids the letters A-Z excluding I, are assigned numbers from 1 to 25, with a number added to the end each time the alphabet is ended, so that A = 1, A1 = 26, A2 = 51, etc., which means that M1 = 25 + 1 = 37) discovered in the second half of December 2020 (period 2020 Y - the year being split into 24 half-months represented by the letters A-Y, with I being excluded).
2020 YM1 has a 320 day (0.88 year) orbital period, with an elliptical orbit tilted at an angle of 2.06° to the plain of the Solar System which takes in to 0.81 AU from the Sun (81% of the distance at which the Earth orbits the Sun) and out to 1.02 AU (102% of the distance at which the Earth orbits the Sun). Although it does cross the Earth's orbit and is briefly further from the Sun on each cycle, 2020 YM1 spends most of its time closer to the Sun than we are, and is therefore classified as an Aten Group Asteroid. Close encounters between 2020 YM1 and Earth are fairly common, with the last thought to have happened in August last year (2020) and the next predicted in October 2026.
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