Tuesday, February 24, 2009

Cometary Meteorites

When the Earth enters a meteoroid stream left by a comet it produces a meteor shower. These showers can be predicted and come every year or so.

A mini Phaeton: How A Cometary Boulder Lit Up The Spanish Sky.

Fireballs (or bolides) are the name given by astronomers to the brightest meteors (popularly referred to as ‘shooting stars’). On 11th July 2008, at 2117 GMT, a brilliant fireball was recorded. At maximum intensity, the object was more than 150 times as bright as the full Moon. It was first picked up at a height of 98.3 km and disappeared from view 21.5 km above the surface of the Earth, tracked by three stations of the Spanish Fireball Network (SPMN) above Bejar, near Salamanca in Spain. At the same time a professional photographer took a picture of the bolide from the north of Madrid.

From these images, the astronomers can deduce the trajectory and properties of the incoming boulder. The team think it was a dense object, about 1 metre across and with a mass of 1.8 tonnes, large enough that some fragments probably survived intact and fell to the ground as meteorites.

The astronomers demonstrate that before its fiery demise, the boulder travelled on an unusual orbit around the Sun, on a path which took it from beyond the orbit of Jupiter to the vicinity of the Earth. This orbit is very similar to that of a cloud of dusty particles (meteoroids) known as the Omicron Draconids, which on rare occasions produces a minor meteor shower and probably originates from the breakup of Comet C/1919 Q2 Metcalf in 1920. This strongly suggests that the boulder was once embedded in the nucleus of that comet.
Trigo-Rodriguez, J.M., et al., Observations of a Very Bright Fireball and Its Likely Link With Comet C/1919 Q2 Metcalf, Monthly Notices of the Royal Astronomical Society, Volume 9999, Issue 9999, Oct 2008

When scientists and historians of the future find archaeological evidence of the Spanish civilization, they are going to compare Trigo-Rodriguez to Ovid, claim that "fireballs" are myths, and call anyone who takes them seriously a pseudoscientist or Velikovskian.

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