Melting of iron close to Earth's inner core boundary conditions and beyond

TL;DR

This study uses a novel X-ray absorption spectroscopy method with laser shock experiments to accurately measure iron's melting curve at extreme pressures, resolving long-standing discrepancies and confirming the validity of dynamic compression techniques for Earth's core conditions.

Contribution

The paper introduces a new experimental approach combining X-ray free electron laser sources with laser shock experiments to determine iron's melting curve at core-like pressures, resolving previous measurement inconsistencies.

Findings

Determined iron's melting boundary up to 420 GPa and 10800 K.

Confirmed agreement between dynamic and static measurements of iron melting.

Resolved controversy over the reliability of dynamic compression data for Earth's core conditions.

Abstract

Several important geophysical features such as heat flux at the Core-Mantle Boundary or geodynamo production are intimately related with the temperature profile in the Earth's core. However, measuring the melting curve of iron at conditions corresponding to the Earth inner core boundary under pressure of 330 GPa has eluded scientists for several decades. Significant discrepancies in previously reported iron melting temperatures at high pressure have called into question the validity of dynamic measurements. We report measurements made with a novel approach using X-ray absorption spectroscopy using an X-ray free electron laser source coupled to a laser shock experiment. We determine the state of iron along the shock Hugoniot up to 420 GPa (+/- 50) and 10800 K (+/- 1390) and find an upper boundary for the melting curve of iron by detecting solid iron at 130 GPa and molten at 260, 380 and 420 GPa along the shock Hugoniot. Our result establishes unambiguous agreement between dynamic measurement and recent extrapolations from static data thus resolving the long-standing controversy over the reliability of using dynamic compression to study the melting of iron at conditions close to the Earth's inner core boundary and beyond.