A magma ocean is a theoretical concept used in planetary science to describe a stage in the early evolution of a rocky planet or moon where the entire surface is covered by a molten silicate magma. This molten layer is thought to have formed during the planet's initial accretion and heat release from radioactive decay. As the magma ocean cools and solidifies, various geological processes such as crust formation, mantle differentiation, and volcanic activity begin to shape the planet's surface and internal structure. Scientists study magma oceans to better understand the early history and evolution of planets and moons in our solar system and beyond.