Saturday 18 July 2020

Asteroid (480936) 2003 QH5 passes the Earth.

Asteroid (480936) 2003 QH5 passed by the Earth at a distance of about 13 000 000 km (33.9 times the average distance between the Earth and the Moon, or 8.69% of the distance between the Earth and the Sun), slightly after 11.10 am GMT on Tuesday 14 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. (480936) 2003 QH5 has an estimated equivalent diameter of 180-570 m (i.e. it is estimated that a spherical object with the same volume would be 180-570 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 14 700-350 000 times as powerful as the Hiroshima bomb. Such an impact would result in an impact crater roughly 3-8 km in diameter and devastation on a global scale, as well as climatic effects that would last decades or even centuries.

 The orbit of (480936) 2003 QH5, and its current position. JPL Small Body Database.

(480936) 2003 QH5 was discovered on 21 August 2003 by the Massachusetts Institute of Technology's Lincoln Near Earth Asteroid Research Laboratory in Socorro, New Mexico. The designation 2003 QH5 implies that it was the 128th asteroid (asteroid H5 - 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 H5 = 8 + (24 X 5) = 128) discovered in the second half of August 2003 (period 2003 Q) while the designation 480936 implies that it was 480 936th asteroid ever discovered (asteroids are not given this longer designation immediately to avoid naming double or false sightings).

(480936) 2003 QH5 has a 517 day (1.41 year) orbital period, with an elliptical orbit tilted at an angle of 17.6° to the plain of the Solar System which takes in to 0.98 AU from the Sun (98% of the distance at which the Earth orbits the Sun, and slightly inside the orbit of the planet Venus) and out to 1.54 AU (154% of the distance at which the Earth orbits the Sun, and slightly 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 this year and the next predicted in February 2017. 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, (480936) 2003 QH5 is also classified as a Potentially Hazardous Asteroid.  
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