Differentiation
The process by which a melted planet or asteroid separates into layers, with heavy metal sinking to form a core and lighter rock floating to form a crust.
Think of salad dressing left to stand: the oil floats above the vinegar. When a young planet or large asteroid melts, something similar happens. Heavy iron-nickel metal sinks to the centre to form a core, lighter rock rich in silicate minerals forms a thick mantle, and the lightest melts rise to make a crust. This sorting is called differentiation. In the early Solar System the heat came mainly from short-lived radioactive elements such as aluminium-26.
Differentiation explains why meteorites are so varied. Chondrites come from bodies that never fully melted, so they still hold their original ingredients. Iron meteorites are mostly pieces of the cores of shattered asteroids. Pallasites mix metal and the green mineral olivine, perhaps from near a core boundary, and eucrites are crust lava.
The Gibeon iron meteorites from Namibia, a IVA iron, show what a core can look like: when cut, polished and etched, they display a criss-cross Widmanstätten pattern that forms only as metal cools very slowly. You can recognise meteorites from differentiated bodies by the absence of chondrules, the small round grains found in chondrites.
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Level: Explorer Ages 10 and up