Magma ocean
A magma ocean is a deep global layer of molten rock thought to have covered the young Moon and possibly other bodies.
A magma ocean is a layer of molten rock hundreds of kilometres deep covering a whole planet or moon. Large impacts and the heat of radioactive elements such as aluminium-26 could melt young worlds on this scale.
The idea came from Apollo samples. Astronauts brought back rocks made almost entirely of calcium-rich plagioclase feldspar. Scientists reasoned that the Moon's outer layers were once molten: dense olivine and pyroxene crystals sank, while lighter plagioclase floated to the top and formed the bright highland crust. The last dregs of melt became rich in potassium, rare earth elements and phosphorus, a material called KREEP.
Magma oceans have also been suggested for Vesta, which may explain the relationship between eucrites and diogenites, and for the early Earth after the giant impact that formed the Moon. Studying meteorites from these bodies helps test how magma oceans crystallised and how quickly they solidified.
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