Police officers called to a suspect explosion in the Thunder Bay area of Ontatio, Canada, late on the evening of Thursday 14 December 2017, have reported a possible meteorite impact. The officers reported finding a hole in the snow about a meter across, close to Highway 61, with a small amount of 'rock-like' material in the centre. Since there were no Human footprints close to the site they suspect a meteorite impact was the most likely cause of the event. The site was inspected on Wednesday 15 December by Stephen Kissen of the Geology Department at Lakehead University, who could not find any traces of meteorite material, though he does not rule out a meteorite as the cause of the incident. Small meteorites are often completely vapourised in explosions 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, and such a superheated small object would have a high chance of being destroyed if it hit a snowfield.
Stephen Kissen of the Geology Department at Lakeview University at the site of the possible Thunder Bay meteorite impact. Lakehead University.
Local media has speculated that the impact might be associated with the Geminid Meteor Shower, however this is unlikely as this is comprised of dust-sized particles from the surface of an object called 3200 Phaethon, which is classed as an Apollo Asteroid (an asteroid with an orbit that crosses that of the Earth), which burn up high in the atmosphere, while objects capable of reaching the ground need to be much larger.
The Thunder Bay 'meteor crater'. Thunder Bay Police Services.
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).
The approximate location of the 14 December 2017 Thinder Bay 'meteorite impact'. Google Maps.
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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