Sunday 27 January 2019

Asteroid 2019 BU1 passes the Earth.

Asteroid 2019 BU1 passed by the Earth at a distance of about 1 147 000 km (2.98 times the average distance between the Earth and the Moon, or 0.77% of the distance between the Earth and the Sun), at about 12.30 pm GMT on Tuesday 22 January 2019. There was no danger of the asteroid hitting us, though were it to do so it would not have presented a significant threat. 2019 BU1 has an estimated equivalent diameter of 11-34 m (i.e. it is estimated that a spherical object with the same volume would be 11-34 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 30 and 12 km above the ground, with only fragmentary material reaching the Earth's surface.

The calculated orbit of 2019 BU1. JPL Small Body Database.

2019 BU1 was discovered on 7 April 20108 by the University of Arizona's Catalina Sky Survey, which is located in the Catalina Mountains north of Tucson. The designation 2019 BU1 implies that it was the 44th asteroid (asteroid U - 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 U1 = 20 + 24 = 44) discovered in the second half of January 2019 (period 2019 B).

2019 BU1 has an 914 day orbital period and an eccentric orbit tilted at an angle of 5.42° to the plane of the Solar System, which takes it from 0.78 AU from the Sun (i.e. 78% of the the average distance at which the Earth orbits the Sun) to 2.90 AU from the Sun (i.e. 290% of the average distance at which the Earth orbits the Sun, slightly less than twice the distance at which Mars orbits). 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). This means that close encounters between the asteroid and Earth are fairly common, with the last having occurred in February 1952 and the next predicted in January 2029.

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