Sunday, 3 June 2018

Asteroid 2018 LA impacts the Earth.

Asteroid 2018 LA is thought to have impacted the Earth somewhere in the Botswana/South Africa border region slightly before 4.45 pm local time (slightly before 6.45 pm GMT) on Saturday 2 June 2018, roughly eight hours after it was discovered by the University of Arizona's Mt. Lemmon Survey at the Steward Observatory on Mount Lemmon in the Catalina Mountains north of Tucson. The Asteroid had an estimated equivalent diameter of 2-6 m (i.e. it is estimated that a spherical object with the same volume would be 2-6 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 more than 40 km above the ground, with only fragmentary material reaching the Earth's surface. The asteroid was initially calculated to have an 82% chance of hitting the Earth over the southern Indian Ocean. Some hours later witnesses in southern Botswana and North West Province, South Africa, reported seeing an exceptionally bright fireball meteor (defined as a meteor brighter than the planet Venus). A revised estimate of the trajectory of the asteroid using additional data from the Asteroid Terrestrial-impact Last Alert System (ATLAS) search program on Mauna Loa suggested that the asteroid could have impacted as far east as Namibia, making it highly likely that the Botswana fireball was 2018 LA.

Bright fireball meteor seen from a farmstead between Ottosdal and Haartbesfontain in North West Province, South Africa, on Saturday 2 June 2018. Barend Swanepoel/Youtube.

2018 LA was discovered at about 11.00 am on 2 June 2018, the designation 2018 LA implying the asteroid was the first such body (asteroid A) discovered in the first half of June 2018 (2018 L). It is estimated to have had an eccentric orbit tilted at an angle of 4.28° to the plane of the Solar System, which takes it from 0.78 AU from the Sun (i.e. 78% of he average distance at which the Earth orbits the Sun) to 1.96 AU from the Sun (i.e. 196% of the average distance at which the Earth orbits the Sun, and further from the Sun than the planet Mars). It is therefore thought to gave been an Apollo Group Asteroid (an asteroid that is on average further from the Sun than the Earth, but which does get closer). It is last thought to have come close to the Earth in May 1987.

Discovery image of 2018 LA. Alex Gibbs/Catalina Sky Survey/Facebook.

Objects of this size probably enter the Earth's atmosphere several times a year, though unless they do so over populated areas they are unlikely to be noticed. They are officially described as fireballs if they produce a light brighter than the planet Venus. It is possible that this object will have produced meteorites that reached the surface (an object visible in the sky is a meteor, a rock that falls from the sky and can be physically held and examined is a meteorite).

 The calculated orbit of 2018 LA. Minor Planet Center.

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