Friday 28 August 2020

Asteroid 2020 QN4 passes the Earth.

Asteroid 2020 QN4 passed by the Earth at a distance of about 272 400 km (0.71 times the average distance between the Earth and the Moon, or 0.18% of the distance between the Earth and the Sun, which is 7.6 times the height of satellites in geostationary orbits), slightly before 4.25 am GMT on Friday 21 August 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 QN4 has an estimated equivalent diameter of 4-11 m (i.e. it is estimated that a spherical object with the same volume would be 4-11 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 43 and 30 km above the ground, with only fragmentary material reaching the Earth's  surface.

The orbit and current position of 2020 QN4. The Sky Live 3D Solar System Simulator.

2020 QN4 was discovered on 22 August 2020 (rhe day 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 QN4 implies that it was the 109th asteroid (asteroid N4 - 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 N4 = (24 x 4) + 13 = 109) discovered in the second half of August 2020 (period 2020 Q - the year being split into 24 half-months represented by the letters A-Y, with I being excluded).

2020 QN4 has a 397 day (1.09 year) orbital period, with an elliptical orbit tilted at an angle of 0.32° to the plain of the Solar System which takes in to 0.80 AU from the Sun (80% of the distance at which the Earth orbits the Sun) and out to 1.31 AU (131% of the distance at which the Earth orbits the Sun). This means that close encounters between the asteroid and Earth are fairly common, with the last thought to have happened in November 2019 and the next predicted in December 2029. 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). 2020 QN4 also has occasional close encounters with the planet Venus, which it last came close to in February 2016.

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