Friday, April 9, 2010

Meteors, Meteorites, and Meteoroids

Meteors, or falling stars, are a common and wonderful sight in the sky. It doesn't take any special equipment to see them, or any special training to enjoy them. They can be seen anywhere that the sky is dark enough for them to show. In some cases, extremely bright ones have been seen in daylight!

Meteors are small objects falling into the Earth's atmosphere from space. Just as spacecraft returning to Earth are surrounded by brightly ionized air due to the friction of the air with the falling spacecraft, the small object is surrounded by brightly lit air, caused by the friction of its entry into the atmosphere. The light mostly comes from the heating of the air. Little or none of the light comes from burning of the meteor itself, normally, though there are some types of meteor where there can be more burning of the material than the norm.


The objects in space are called meteoroids, before they encounter the Earth. They are not a special class of objects, it's just a general term for small objects like bits of dust, small rocks, and so on. They can have a number of sources.


The term meteor refers to the event of the meteoroid passing through the atmosphere. This is the show we get to enjoy. As an event, it has a name, just like "rainstorm" is a name for an event. It's not a name for a "thing", so to speak.


A meteorite is a thing, on the other hand. It's what we call the material of the meteoroid that reaches the surface of the Earth.


Chondrites (pronounced kon-drites) are the most common meteorites. They are remnants of the earliest material that formed in the solar system around the Sun. The name chondrite refers to the chondrules (kond-rools) that they're made of--little blobs of rock.

Close Up of a Chondrite, Showing Chondrules

Chondrules Rubbed Out of a Chondrite

One type of chondrite is rare among chondrites, this is the Carbonaceous Chondrite. The name refers to the fact that it's got a lot of carbon in it. This gives it a black color. Carbonaceous condrites are the earliest of the chondrites.

Carbonaceous Chondrites

All chondrites come from small bodies that formed in the early solar system that never got large enough to form enough heat to melt down the various materials that they are made of, and separate them. For example, in the Earth the materials it was made of did melt. The iron and nickle and other heavy metals sunk to the center of the Earth for the most part, and the lighter "rocky" materials stayed in the Earth's outer crust.

There are meteorites that come from larger bodies that did melt and separate the materials that are all mixed together in chondrites. The ones that were once in the core of these larger bodies are the iron meteorites.

Campo del Cielo Iron Meteorite, photo courtesy of Meteor Recon

Iron Meteorite

Photo courtesy of Meteorite Recon

Since most iron meteorites formed in a much smaller body than the Earth, the iron in them cooled in an environment where the metal formed large crystals that can only form in a low gravity environment where cooling is very slow. Iron meteorites can be cut, polished, and etched to show these beautiful crystal patterns, known as Widmanst├Ątten or Thomson patterns.

Crystal Patterns in Iron Meteorite

Some meteorites are pieces of larger bodies in space. Pieces of the Moon and Mars have been identified. These meteorites are the result of a meteorite hitting the Moon or Mars hard enough to knock pieces of them off into space!

Some are pieces of asteroids. One type of meteorite, called a Pallasite, are believed to be pieces of the asteroid Vesta. They are especially beautiful, and are often turned into jewelry.



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