Monday, 9 November 2015

Bright fireball over Saskatchewan and Manitoba.

Many people have reported seeing a bright fireball over parts of southern Saskatchewan and Manitoba at about 8.40 pm local tine on Sunday 8 November 2015. A fireball is defined as a meteor (shooting star) brighter than the planet Venus. These are typically caused by pieces of rock burning up in the atmosphere, but can be the result of man-made space-junk burning up on re-entry. The bright lights seen in fireballs are caused by airbursts in which rocky meteorites explode due to friction induced heating high in the atmosphere, and any fragments reaching the ground usually do so several minutes later. On this occasion many people reported hearing sonic booms in the area around Kelvington in east central Saskatchewan, which astronomer Martin Beech of the University of Regina suggests may indicate that the object broke up low in the atmosphere, potentially with fragments reaching the ground.

The 8 November 2015 fireball meteor seen from Ralph, Saskatchewan. Bill Allen/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, though unlikely, 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), though most meteorites come from larger objects that penetrate further into the atmosphere before exploding, and therefore have a better chance of producing fragments that reach the surface.

On this occasion the meteor is thought likely to be part of the Taurid Meteor Shower, which lasts from about 10 September to about 10 December, with two peaks on 12 November and 10 October. The Taurids are associated with Comet Encke, and occur as the Earth passes through the trail of the comet, though the comet is an ancient resident of the Inner Solar System, probably having been here for 20 000-30 000 years, and over that time has largely disintegrated due to the heat of the Sun (a fate which eventually overtakes any comet which is knocked from its orbit in the Outer Solar System into the Inner Solar System), meaning that fragments of the comet are scattered in a wide area loosely following the orbital path of the comet. The Taurids are unusual for a meteor shower in that they never produce the large number of small meteors seen at the peak of other such showers, but rather a small number of bright, large fireballs, suggesting large pieces of more durable material than cometary ice have been shed over time as the comet has slowly broken up.

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