Friday 7 August 2020

Asteroid 2020 NK1 passes the Earth.

Asteroid 2020 NK1 passed by the Earth at a distance of about 8 228 000 km (21.4 times the average distance between the Earth and the Moon, or 5.50% of the distance between the Earth and the Sun), slightly before 9.00 pm GMT on Friday 31 July 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 NK1 has an estimated equivalent diameter of 300-940 m (i.e. it is estimated that a spherical object with the same volume would be 300-940 m in diameter), and an object of this size would be predicted to be capable of passing through the Earth's atmosphere relatively intact, impacting the ground directly with an explosion that would be 65 000-2 650 000 times as powerful as the Hiroshima bomb. Such an impact would result in an impact crater roughly 4-13 km in diameter and devastation on a global scale, as well as climatic effects that would last decades or even centuries.

Radar range-Doppler image of 2020 NK1 taken on July 2020. The image resolution in the vertical dimension is 30 m per pixel. Arecibo Observatory/NSF/NASA.

2020 NK1 was discovered on 13 July 2020 (18 days before 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 NK1 implies that it was the 34th asteroid (asteroid K1 - 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 K1 = (24 x 1) + 10 = 34) discovered in the first half of July 2020 (period 2020 N - the year being split into 24 half-months represented by the letters A-Y, with I being excluded).

The orbit of 2020 NK1, and its current position. JPL Small Body Database.

2020 NK1 has a 601 day (1.65 year) orbital period, with an elliptical orbit tilted at an angle of 45.4° to the plain of the Solar System which takes in to 0.49 AU from the Sun (49% of the distance at which the Earth orbits the Sun, and slightly outside the orbit of the planet Venus) and out to 2.30 AU (230% of the distance at which the Earth orbits the Sun, and comsiderably outside the orbit of the planet Mars). This means that close encounters between the asteroid and Earth are fairly common, with the last thought to have happened in March 2019 and the next predicted in February 2024. 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). As an asteroid probably larger than 150 m in diameter that occasionally comes within 0.05 AU of the Earth,2020 NK1 is also classified as a Potentially Hazardous Asteroid. 2020 NK1 also has occasional close encounters with the planets Venus, which it last came close to in December 1959 and is next predicted to pass in August 2030.

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