The UPM contributes to international study revealing how iron deforms under Earth's core conditions
The research, published in Nature Communications, combines extreme experiments conducted at the National Ignition Facility with molecular dynamics simulations developed in Spain and Argentina to understand how iron deforms at the atomic scale.
17.07.2026
An international research team succeeded, for the first time, in simultaneously measuring the dynamic strength of iron under pressure and temperature conditions comparable to those of Earth's inner core. The study, published in Nature Communications, combines experiments conducted at the National Ignition Facility (NIF) at Lawrence Livermore National Laboratory in the United States with advanced computational simulations to understand how iron deforms in one of the planet's most extreme environments.
The research involves the participation of the Universidad Politécnica de Madrid through Carlos Ruestes—a Ramón y Cajal researcher affiliated with the “Guillermo Velarde” Institute of Nuclear Fusion, ETSI Industriales, UPM and the only author affiliated with a Spanish or European institution. His contribution focused on molecular dynamics simulations carried out as part of the study's computational component.
“Experiments allow us to achieve extraordinary conditions, but to understand what happens inside the material, we also need to analyze its response at the atomic scale. Molecular dynamics simulations make it possible to link experimental observations with the microscopic mechanisms governing iron deformation,” explains Carlos Ruestes, a co-author of the study.
Recreating Earth’s deep interior
Iron is a major constituent of the cores of Earth and other rocky planets. However, measuring its mechanical properties under pressures of millions of atmospheres and temperatures of several thousand degrees poses an immense experimental challenge.
To address this issue, the team used the National Ignition Facility, a laser facility capable of generating conditions comparable to those of Earth’s deep interior for extremely brief intervals. Laser pulses compressed iron samples, reaching pressures on the order of three million atmospheres and temperatures near 5,000 degrees Celsius.
Using ultrafast X-ray diagnostics and optical techniques, the researchers tracked the material's evolution as it deformed. The experimental response was analyzed based on the growth of instabilities induced in the sample, allowing the researchers to infer the strength of the iron under these extreme conditions.
From Experiment to Atomic Scale
Interpreting the results required combining different levels of simulation. Hydrodynamic simulations made it possible to reconstruct the overall evolution of the experiment, while molecular dynamics simulations revealed how the material responded at the atomic scale.
Researchers from the University of Mendoza and the Universidad Politécnica de Madrid participated in the molecular dynamics component of the study. These simulations allowed for an analysis of how the initial crystalline orientation of the iron and pressure-induced structural transformations alter its mechanical strength.
One of the most significant findings was the identification of unexpected behavior associated with the phase transition of iron under pressure. During compression, atoms rearrange themselves, and the material undergoes a change in its crystalline structure. This transformation also alters the microstructure, creating small grains that can decisively influence the material's mechanical response.
The team observed that iron under high pressure exhibits varying levels of strength depending on the crystalline orientation of the initial phase. Specifically, certain orientations produce a high-pressure phase that is consistently stronger than others contrasting with the trends observed under ambient conditions.
Large-scale molecular dynamics simulations reproduced this same trend and helped identify its likely origin: the way different crystalline orientations undergo the phase transition and subsequently deform within the high-pressure structure.
"This result demonstrates that, even under pressures of millions of atmospheres, the material's structural history remains significant. The initial orientation and the phase transformation determine the resulting microstructure and, consequently, the material's mechanical response," points out Ruestes.
Implications for Geophysics and Extreme Materials
Understanding the strength of iron and its dependence on microstructure is relevant to interpreting the dynamics of Earth's inner core. The way iron deforms and flows under extreme conditions can influence seismic anisotropy, that is, the directional dependence of seismic wave propagation speeds within the inner core.
These phenomena are linked to the structure and evolution of Earth's deep interior and can provide insights into the core's dynamic history and its relationship with Earth's magnetic field.
The results also have broader implications for the study of materials subjected to extreme conditions and for understanding the interiors of other rocky planets and exoplanets with iron-rich cores.
An international collaboration with Spanish participation
The study brings together researchers from Lawrence Livermore National Laboratory, the University of California San Diego, the University of Mendoza, SLAC National Accelerator Laboratory, Stanford University, and the Universidad Politécnica de Madrid. Thus, this project solidifies a scientific collaboration among the United States, Argentina, and Spain in the study of materials under extreme conditions.
“This work demonstrates the value of integrating large-scale experimental facilities with advanced computational simulation. It also shows that Ibero-American universities can make direct contributions to cutting-edge scientific problems that require a close connection between experiments, theory, and high-performance computing,” concludes Ruestes.