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Meteors and Meteorites. Meteors - Matter that falls through Earth’s atmosphere. Often called “shooting stars”. A few can be observed every hour. Meteoroid is the term used for a piece of matter before it enters the atmosphere. A meteorite is a meteor that hits the ground.
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Meteors- Matter that falls through Earth’s atmosphere. Often called “shooting stars”. A few can be observed every hour.
Meteoroid is the term used for a piece of matter before it enters the atmosphere.A meteorite is a meteor that hits the ground.
The difference in meteoroids and asteroids is size. The distinction is fuzzy: meteoroids are generally less than 100 km in diameter.
This size distinction only exists in space. When an asteroid hits the Earth’s atmosphere, it becomes a meteor.
Cometary fragments can be dislodged when a comet is near the Sun. These dust or pebble-sized particles form a meteoroid swarm.
Over time these micrometeoroids are spread out over the entire orbit of the comet.
When the Earth crosses the orbit of a young, relatively undispersed cluster of meteoroids, a meteor shower occurs.
Meteor shower 19th century engraving
The intersections occur at the same time each year. Meteor showers are named for their radiant(the constellation from which they appear to radiate).
As far as we know, no meteor shower particle has ever reached the ground (none is large or dense enough). However, some pieces have been collected by high-altitude U2 aircraft flights.
Larger meteoroids, ones more than a few cm in diameter, are usually not associated with swarms of cometary debris.
These larger meteoroids are responsible for most of the cratering of the Moon, Mercury, Venus, Mars, and all the Jovian moons.
On Earth, meteors have a typical entry velocity of approximately 20 km/s. They produce “shock waves” in the air. Some even produce sonic booms.
Some produce bright sky streaks that may last several seconds and can be seen for several hundred miles. These are often called “fireballs”.
More massive meteors, 1 ton and 1 meter across, produce craters. The Barringer crater in Arizona is one example.
The meteorite that produced the Barringer Crater was 50,000 tons.
The Earth has 100 craters larger than 0.1 km in diameter. Many are only visible from satellites.
The following is an underground resonance image of the Yucatan Peninsula crater that was formed by the asteroid impact that eventually killed the dinosaurs.
This is how that collision may have appeared to the dinosaurs.
On June 30, 1908 a meteor exploded above the Tunguska plain in Siberia. This was equal to a 1 megaton nuclear explosion.
When asteroids’ orbits are reconstructed, most intersect the asteroid belt; so this is probably where they originated.
Meteorites - several thousand have been found. Two basic types are finds and falls.
Finds are meteorites that people “find” on the ground, without seeing them fall.
Finds tend to be unusual looking. Many are found in Antarctica. (Both of these conditions make the meteorites easier to see.)
Fallsare meteorites that are found after they are seen to fall to Earth.
CompositionFireballs tend to be 0.5 g/cm3 in density (like comets). Meteorites average 5 g/cm3 (like asteroids).
Another way to distinguish meteorites is by their composition:Irons - 7 g/cm3Stones - 3 g/cm3Stony-irons - a mixture of the two.
