Magma ocean
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Magma oceans are vast fields of surface magma that exist during periods of a planet's or some natural satellite's accretion when the celestial body is completely or partly molten.[1]
In the early Solar System, magma oceans were formed by the melting of planetesimals and planetary impacts.[1] Small planetesimals are melted by the heat provided by the radioactive decay of aluminium-26.[1] As planets grew larger, the energy was then supplied from giant impacts with other planetary bodies.[2] Magma oceans are integral parts of planetary formation as they facilitate the formation of a core through metal segregation[3] and an atmosphere and hydrosphere through degassing.[4] Evidence exists to support the existence of magma oceans on both the Earth and the Moon.[1][5] Magma oceans may survive for millions to tens of millions of years, interspersed by relatively mild conditions.