Earth's Core May Be 1,000°C Cooler Than Thought — Reshaping Our Understanding of the Planet's Interior

For decades, textbooks have put the temperature of Earth's molten outer core at roughly 6,000°C — comparable to the surface of the Sun. A new measurement technique suggests that figure may be off by as much as 1,000°C, with profound implications for how scientists understand the planet's magnetic field, geological history, and the evolution of its deep interior.

Researchers presented the findings at the Goldschmidt Conference in Montreal on July 17, based on a novel method for measuring the melting temperature of iron under the extreme pressures found in the core. By compressing tiny iron samples between diamond anvils and heating them with lasers while simultaneously taking X-ray diffraction measurements, the team determined that iron melts at significantly lower temperatures than previously assumed at core-equivalent pressures — as much as 1,000°C lower than the canonical estimates.

The discovery helps resolve a long-standing paradox in geophysics. Earth's magnetic field, generated by the churning of liquid iron in the outer core, has existed for at least 3.5 billion years. But if the core were as hot as previously thought, the solid inner core — which helps drive the convection that sustains the magnetic field — would have formed much later than the evidence suggests. A cooler core means the inner core could have begun solidifying earlier, neatly explaining the magnetic field's longevity.

The findings also have implications for exoplanet research. The temperature of a planet's core determines how long it can sustain a magnetic field, which in turn influences whether an atmosphere can survive against stellar radiation. If planetary cores are systematically cooler than models predict, the habitable window for Earth-like exoplanets may be wider than currently assumed.