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 Meteorite Histories

Asteroids are made of some of the oldest materials in the solar system.

Asteroids formed more than 4.5 billion years ago out of the same rocky materials as the planets. Some of them have not changed since they were born. Others melted, formed layers, or were broken apart by collisions.

1. Formation

 

2. Layering

 

Countless large asteroids were assembled from chunks of material in the early solar system.

 

When some of the largest asteroids melted, iron sank to their centers and formed cores. Lighter rock floated up to create mantle and crust layers.

3. Activty

 

4. Undisturbed Asteroid

 

5. Fragmenting and Asteroid

  

In a volcanically active asteroid, magma flows up to the surface from molten areas in the mantle. Lava flows have been found on several asteroids.

 

An asteroid that has not been broken apart in collisions may have a core, mantle, and crust. Its surface may be smooth or cratered.

 

Collisions break apart large asteroids, scattering fragments through space. The mineral content of each piece tells us where it formed in the original asteroid.


Types of Meteorites

meteorite model

Stony Meteorites

 

Stony-iron Meteorites

 

Iron Meteorites

More than 85 percent of meteorites that fall to Earth are stony. They originate in asteroids with mantles and crusts, and contain minerals similar to those in Earth rocks. Some meteorites formed when rock inside their parent asteroids melted completely. Others came from partially melted rock, while the rest originated in asteroids that never melted. Many meteorites contain chondrules, spheres of minerals that are among the oldest unchanged materials in the solar system.

rocks

 

Many stony-iron meteorites come from the thin zone of melted rock that lies between an asteroid’s mantle and core. These meteorites contain deoplets of the silicate mineral olivine trapped in the iron This translucent, olive-green mineral forms in heated rocks and is common on Earth. Meteorites with olivine in them are rare and beautiful.

rocks

 

These meteorites come from the heavy iron cores of layered asteroids. They are scattered throughout space when collisions smash their parent bodies into pieces.

In asteroids that melted, iron sank to the cores. Over long periods of time, the cores cooled slowly, allowing iron crystals to grow. These crystals show up as cross-hatched patterns when an iron meteorite is sliced, polished, and etched with acid.

rocks

rocks

This is a polished section of a stony meteorite that fell to Earth and was found in northwest Africa. It is part of the debris from asteroids that collided long ago. When objects in space run into one another at high speeds, they generate an enormous amount of energy on impact. It’s enough to heat them and break them into pieces. This slice came from a meteorite that wandered through space for a long time before falling to Earth. Note the many shiny iron flecks in the dark silicate background.

 rocks

This stony-iron meteorite was found in Chihuahua, Mexico, in 1909. Its mineral content reveals that it came from the thin boundary between the core and mantle of an asteroid that was smashed to pieces long ago. The meteorite is made of iron and the mineral olivine, polished here to a mirrorlike finish. The olivine crystallized from magma (molten rock) deep inside an asteroid. As it cooled, it sank to the center and settled on top of the iron core. The olivine in this meteorite would look like olive-colored glass if it were lit from behind.

 rocks

Asteroids that melt can separate into several layers, including an iron core. During a collision, the core splits into heavy iron fragments. When those pieces fall to Earth, we find them as iron meteorites. This one came from an asteroid that melted, cooled, and was shattered in a collision. The size and shape of the iron crystals tell us that the original core took a while to cool, giving the crystals enough time to form.