Sunday 27 October 2019

Asteroid 2019 UE4 passes the Earth.

Asteroid 2019 UE4 passed by the Earth at a distance of about 407 700 km (1.06 times the average  distance between the Earth and the Moon, or 0.27% of the distance between the Earth and the Sun), slightly after 10.05 pm GMT on Monday 21 October 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 UE4 has an estimated equivalent diameter of 6-18m (i.e. it is estimated that a spherical object with the same volume would be 6-18 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 38 and 24 km above the ground, with only fragmentary material reaching the Earth's surface.

The calculated orbit of 2019 UE4. JPL Small Body Database. 

2019 UE4 was discovered on 23 October 2019 (two days after its closest approach to the Earth) by the Atlas MLO Telescope at Mauna Loa Observatory in Hawaii. The designation 2019 UE4 implies that the asteroid was the 101st object (object E4 - in numbering asteroids the letters A-Z, excluding I, are assigned numbers from 1 to 25, so that E4 = (24 x 4) + 5 = 101) discovered in the second half of October 2019 (period 2019 U).

2019 UE4 has a 573 day orbital period and an eccentric orbit tilted at an angle of 1.05° to the plane of the Solar System, which takes it from 0.80 AU from the Sun (i.e. 80% of he average distance at which the Earth orbits the Sun) to 1.90 AU from the Sun (i.e. 190% of the average distance at which the Earth orbits the Sun, beyond 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 2019 UE3 occasionally comes close to the Earth, with the last such encounter having happened in May 2016, and the next predicted for May 2024. 2019 UE3 also has occasional close encounters with the planet Venus, with the next close encounter predicted in December 2046, and Mars, which it last came close to in October 1987 and is predicted to pass again in November 2024.

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