Thursday 15 August 2019

Asteroid PS1 passes the Earth.

Asteroid 2019 PS1 passed by the Earth at a distance of about 827 000 km (2.01 times the average  0distance between the Earth and the Moon, or 0.55% of the distance between the Earth and the Sun), slightly before 5.30 pm GMT on Friday 9 August 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 PS1 has an estimated equivalent diameter of 8-26 m (i.e. it is estimated that a spherical object with the same volume would be 8-26 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 35 and 20 km above the ground, with only fragmentary material reaching the Earth's surface.

 The calculated orbit of 2019 PS1. JPL Small Body Database.

2019 PS1 was discovered on 10 August 2018 (the day after its closest approach to the Earth) by the Zwicky Transient Facility at Palomar Observatory in California. The designation 2019 PS1 implies that it was the 42nd asteroid (asteroid S1 - 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 S1 = 18 + (24 X 1) = 42) discovered in the first half of August 2019 (period 2019 P).

2019 PS1 has a 703 day orbital period and an eccentric orbit tilted at an angle of 2.00° to the plane of the Solar System, which takes it from 0.90 AU from the Sun (i.e. 90% of he average distance at which the Earth orbits the Sun) to 2.19 AU from the Sun (i.e. 219% of the average distance at which the Earth orbits the Sun, and considerably outside the orbit of the planet Mars). 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 occasionally occur, with the last having occurred in March this year, and the next predicted for April 2021.

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