Asteroid 2021 AE passed by the Earth at a distance of about 464 800 km (1.21 times the average distance between the Earth and the Moon, or 0.31% of the distance between the Earth and the Sun), slightly before 2.30 am GMT on Thursday 31 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. 2021 AE has an estimated equivalent diameter of 13-40 m (i.e. it is estimated that a spherical object with the same volume would be 13-40 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) between 23 and 10 km above the ground, with only fragmentary material reaching the Earth's surface.
2021 AE was discovered on 2 January 2021 (two days after its closest approach to the Earth) by the Asteroid Terrestrial-impact Last Alert System (ATLAS) search program's HKO Telescope on Mount Haleakala, Hawai'i. The designation 2021 AE implies it was the fifth asteroid (asteroid E; 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 E = 5) discovered in the first half of January 2021 (period 2021 A; the year being split into 24 half-months represented by the letters A-Y, with I being excluded).
2021 AE has a 728 day (1.99 year) orbital period, with an elliptical orbit tilted at an angle of 7.71° to the plain of the Solar System which takes in to 0.70 AU from the Sun (70% of the distance at which the Earth orbits the Sun, and slightly inside the orbit of the planet Venus) and out to 2.47 AU (247% 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). Asteroid 2021 is predicted to make another close pass of the Earth in December next year (2021).
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