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TITLE: Commonly Asked Questions

[Photo: Meteroid, Meteor, and Meteorite]

Meteoroid, Meteor, Meteorite What's the Difference?

A meteoroid is a natural fragment of rock less than 1 km (.6 mi) across that orbits the Sun.

A meteor is the streak of light caused when a meteoroid enters Earth's atmosphere. Air friction melts the meteoroid's surface, making it glow white hot. Meteors also are called shooting stars.

A meteorite is a meteoroid that survives the fiery passage through the atmosphere and crashes to Earth. Most meteorites come from asteroids, but a few are from Mars and the Moon.

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How Old are Meteorites?
Every meteorite has three different ages:

1) Absolute age is when the rock first formed. Most meteorites are 4.5-4.6 billion years old.

2) Exposure age is the time the rock spent as a small fragment drifting in space, exposed to cosmic radiation. For most stony meteorites, this was less than 50 million years. Irons show a greater range of ages.

3) Terrestrial age is the amount of time the meteorite has spent on Earth.


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What are Meteorites Made Of?
Minerals. Some of the minerals are the same ones seen in Earth rocks. Others are not found on Earth at all. But in both cases, the minerals in meteorites provide clues to the rocks' origins.

Cape York Iron-and nickel-rich alloy minerals kamacite and taenite surround a brassy nodule of troilite, an iron sulfide mineral. These minerals are extremely rare in terrestrial rocks.

Peña Blanca Spring This meteorite is largely composed of enstatite, an iron-free variety of pyroxene. Pyroxene is common on Earth.

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Smithsonian National Museum of Natural History Department of Mineral Sciences website Credits