Harrison Nicholls

After the impact that created the Moon, Earth became a liquid ball. Gravitational 'kneading' heated the planet, prolonging the magma ocean's life from 30 to 500 million years—depending on oxygen levels. Water vapor trapped heat, and weak tides enriched the air with hydrogen. This paints a picture of

Scientists modeled the thermal evolution of sub-Neptunes and found that 98% of these worlds probably harbor a permanent magma ocean under their hydrogen atmosphere. This explains why the most common planet type in the galaxy stays hot inside, even though they were thought to have solidified long ago