Most people are familiar with the term “shooting star,” but few know its importance. Read More
Actually, it is not a star shooting across the sky, but a small piece of solid matter called a meteoroid colliding with the atmosphere. As the meteoroid enters the Earth’s atmosphere, the friction created by its incoming velocity causes its surface to heat up, and the brilliant flash of light records the passage of a meteor. Should the object survive this firey plunge through the atmosphere and hit the ground, it then becomes a meteorite. On very rare occasions when an extremely bright meteor is observed, it is referred to as a fireball. It is from these fireballs that most meteorites of recoverable size originate. Meteorites recovered in this manner are termed falls, indicating that the specimen was observed while falling. The majority of meteorites are recorded as finds, those specimens which were not observed to fall.
As compared to Earth rocks, meteorites have several features which can be used to establish their extraterrestrial origin. The surface of a meteorite is generally very smooth and featureless, but often has shallow depressions and deep cavities resembling clearly visible thumbprints in wet clay. Meteorites which have fallen recently may have a black “ash-like” crust on their surface. This provides evidence of their flaming entry through the atmosphere. However, this crust weathers to a rusty brown color after several years of exposure on the Earth’s surface and will eventually disappear altogether.
The Three Main Types of Meteorites. Although there are a large number of sub classes, meteorites are divided into three main groups: irons, stones and stony-irons. Almost all meteorites contain extraterrestrial nickel and iron, and those that contain no iron at all are so rare that when we are asked for help and advice on identifying possible space rocks we usually discount anything that does not contain significant amounts of metal. The three types of meteorites are: Nickel Iron, Pallasite, and Stone Meteorites.