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