Tuesday 14 July 2020

Fragments of meteorite believed to have come from the July Fireball found in Narashino, Japan.

A fireball meteor (a meteor brighter than Venus is considered to be a fireball) was witnessed by many people over the Kanto Region of Japan on Thursday 2 July 2020. Following this event a resident of a condominium in the city of Narashino in Chiba Prefecture, was awoken by a loud crash, discovered a fragment of rock on the communal landing outside her home, which she collected in the belief that it might be a meteorite. Noting that the handrail outside her home had been damaged, she later found a second fragment in the courtyard below, and took both to the National Museum of Nature and Science in Tokyo. On Monday 13 July 2020 scientists at the museum announced that they had been able to confirm the extra-terrestrial nature of the rock, by the detection of isotopes of aluminium, sodium, and manganese, which have extremely short half-lives, but which are constantly formed on the surface if asteroids by the actions of cosmic rays.

Two fragments of meteorite found in Narashino, Japan, following a fireball meteor over the Kanto Region on 2 July 2020. National Museum of Nature and Science/Kyodo News.

The two fragments of meteorite weigh 63 and 70 g, with the specimen which was found second having a brownish colour, believed to be caused by exposure to rain, which caused iron on its surface to oxidise (rust). The two meteorites appear to fit together, and are thought to have been part of the same object that broke upon impact, possibly with the damaged handrail.

A close fit between the two pieces of the Narashino Meteorite suggests they were part of the same object. National Museum of Nature and Science/Kyodo News.

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. The brightness of a meteor is caused by friction with the Earth's atmosphere, which is typically far greater than that caused by simple falling, due to the initial trajectory of the object. Such objects typically eventually explode in an airburst called by the friction, causing them to vanish as an luminous object. However this is not the end of the story as such explosions result in the production of a number of smaller objects, which fall to the ground under the influence of gravity (which does not cause the luminescence associated with friction-induced heating).

These 'dark objects' do not continue along the path of the original bolide, but neither do they fall directly to the ground, but rather follow a course determined by the atmospheric currents (winds) through which the objects pass. Scientists are able to calculate potential trajectories for hypothetical dark objects derived from meteors using data from weather monitoring services.
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