Meteorite Information

 

Until about 150 years ago, most people thought rocks did not fall to earth from outer space. Only people who had witnessed it, or knew of it actually happening believed that rocks fell from the sky. Others thought such an idea was crazy. But science soon caught up with the stories, and rocks from space or meteorites became a reality.

 

Craters on the Moon and other planets were once, thought to be created by old volcanoes. This concept was thought to be the same for Earth too, but around the year 1900, it was proven otherwise at a place now called Meteor Crater in Arizona. Rocks, including large ones, do collide or fall to the Earth, the Moon and other planets such as Mars. Many believe that the dinosaurs were killed off by a large (6 miles in size) meteor collision with Earth. Large impact craters create new rocks called tektites, which are like volcanic glass, and impact melts called breccias, and fractured rocks called shattercones.

 

"Shooting Stars" were once thought to be stars falling from their place in the heavens, never to be seen again. But we now know that these shooting stars are actually meteors that pass through our atmosphere. The typical shooting star is a small spec of rock that burns up in our atmosphere from friction. If a bigger meteor fell you would definitely notice a difference in the brightness and size of the streak. A large meteor seen locally would brighten the sky in the daytime, and often creates a "sonic boom".

 

Meteorites are meteors that land on Earth. They are called a Fall if witnessed by people when they fall, or Finds when people find them and no one saw them come down in an area. A new or recent fall will typically have a dark, often black "fusion crust" on one or more sides which demonstrates the heat generated during its’ flight through our atmosphere. The rocks get cooked, and melt away. Crust colors can vary with different types of meteorites.

 

Most meteorites have a nickel-iron metal in them that is attracted to magnets. This attraction to magnets is called paramagnetism. Most achondrites have very little metal are not attracted to magnets or metal detectors.

 

Where do meteorites come from? The main source of meteorites is from the Asteroid Belt, which lies between Mars and Jupiter. This belt is full of orbiting asteroids that range in size from small particles to rocks up to 10 miles in length. These pieces are thought by some to be the parts of a planet that never came together. When asteroids collide with each other, they create new pieces that may fall out of orbit towards Earth, or to other planets or moons that eventually may grab them by gravity forces. They often hit a planet’s atmosphere moving at 10,000 to 20,000 MPH (WOW). Other sources of meteorites include the Moon, Mars, and comets.

 

Most meteorites are thought to be about 4.56 billion years old, which is slightly older than Earth. Planetoid meteorites including the Mars and the Moon are usually younger.

 

There are three main types of meteorites. Stone(93%), Iron(6%) and Stony-iron(1%). 86% of the total represent stones are estimated to be from the undifferentiated (unchanged or changed little) or chondrite (stone) category. About 7% of the total are differentiated (changed a lot) stones that are called Achondrites. A very small % are unique, one of a kind types that don’t easily fit into a distinct category. These estimates are based on the recorded falls, and the types that have fallen with them, and by number of finds.

 

Stone meteorites are split into two major categories: Chondrites (starts with a ‘k’ sound) and Achondrites, meaning rocks with or without chondrules, which are small rounded ball-like structures made only out in space. You will not find rocks made on planets , like Earth, that have chondrules in them. The details on how chondrules are made are still a mystery. Many ideas have been proposed, but we still don’t know for sure.

 

Most meteorites that are from the Asteroid Belt are Chondrule filled stony rocks with a little to a lot of metal inside. Others are the Iron (iron-nickel) rocks that are all metal, or a unique mixture of both kinds, the Stony-Irons. Achondrites do occur in the Belt, and are usually associated with larger planet-like differentiated pieces. Mars and Moon meteorites are also Achondrites, and they are obviously closer to us than the Asteroid Belt asteroids are.

 

 

 

Summary of Meteorite Types

 

 

Chondrites (Stone)

There are about 15 different named types of Chondrites including:

 

H or high metal

L or low metal

LL or very low metal

Various C-meteorites for Carbonaceous (comets are thought to be in this class)

Achondrites (Stone)

There are about 10 different types of Achondrites including:

 

Shergottites, Nakhlites, and Chassignite

Lunar (from the Moon)

Eucrites

Diogenites

Howardites (mixture of Eucrites and Diogenites)

Aubrites

Angrites

Urelites

Stony-Iron

There are two types of Stony-Iron meteorites:

 

Pallasite

Mesosiderite

Iron

There are three main types of Iron meteorites with many sub-categories

 

Hexahedrite

Octahedrite

Ataxite

 

 

Facts and Fiction of Falls and Finds

 

Meteorite Falls:

 

Meteorite Falls can happen all over the earth. Most fall into the oceans that cover the majority of earth.

What we usually see as a falling star is just a small bit of rock that burns up in the atmosphere.

Fireball’s which can "light up the sky", day or night, are the meteors that will produce meteorites. They often start out a chunk as big as a car or so, only to break up and burn away to usually less than a hundred pounds for the total weight of meteorites found for a particular fall.

Witnessed falls are usually given the name of the nearest town or landmark. The same can be said for most finds.

Fresh fusion crust is probably the most obvious feature of a new fall. It does not take long for the effects of earth to start breaking down a meteorite.

 

Meteorite Finds:

 

Finds can also happen all over the earth. The majority however are found in the desert regions of the world, particularly north Africa and the middle east. Antarctica is also a rich location for meteorites finds. The reduced weathering effect in these regions is one of the reasons more are found. Wet or jungle like climates/terrain make finding falls and new finds difficult.

Iron meteorites are found more often (higher %) than they actually fall because they are more durable over time, and they look like what people think are meteorites.

 

Meteorite Tidbits:

 

They are not hot when they first land on earth. Maybe warm.

They are not radioactive, nor do they have healing powers.

They are hard to find and difficult to acquire or purchase????

To date, not one person has been reported killed by a meteorite.

 

 

1/0