Ironing out the interiors of exoplanets

An artist's conception of a super-Earth with the NIF target chamber superimposed over the mantle, looking into the core. Credit: John Jett.

Modelling the interior structure and dynamics of extra-solar planets has been created because of the discovery. It turns out that iron plays a role.

The high-pressure melting curve and structural properties of pure iron up to 1,000 GPa were determined using lasers at the National Ignition Facility. Science has the research in it.

The team performed a series of experiments that mimicked the conditions observed by a parcel of iron descending toward the center of a super-Earth core. The NIF Discovery Science program gives all researchers access to the experiments.

Rick Kraus is a physicist at the National Laboratory and the lead author of the paper. The iron melting curve is critical to understanding the internal structure, thermal evolution, as well as the potential for dynamo-generated magnetospheres.

It is believed that a magnetosphere is an important component of the planets. Earth's magnetodynamo is generated in the convecting liquid iron outer core surrounding the solid iron inner core and is powered by the heat released during solidification of the iron.

Accurate and precise physical properties at extreme pressure and temperatures are required to predict what is happening in the interiors of planets with iron. The melting point of iron is still being debated for the conditions of Earth's interior. The melt curve is the largest rheological transition a material can undergo. The temperature depends on the pressure of the iron.

The team determined the length of the dynamo action during core solidification to the hexagonal close-packed structure.

Kraus said that exoplanets with four to six times Earth's mass have the longest dynamos, which provide important shielding against radiation.

Kraus said that the technique for iron developed will be applied to more programmatically relevant materials in the future.

The equation of state model has an incredibly sensitive constraint on the melt curve.

The team was able to observe the equilibrium phase boundary because of the evidence that the solidification process is fast. Kraus said that the experimental insight is improving the modeling of the time- dependent material response.

Other team members include Suzanne Ali, Jon Belof, Dayne Fratanduono, and Philip Myint. Researchers from the University of Illinois at Chicago, the Carnegie Institute for Science, University of Rochester, Sandia National Laboratory, California Institute of Technology, University of California Davis and University of California Los Angeles contributed to the study.

Richard G. Kraus is the author of Measuring the Melting Curve of Iron at Super-Earth Core Conditions. www.science.org/doi/10.1126/science.abm1472

Science journal information.

Ironing out the interiors of exoplanets was retrieved fromphys.org on January 14, 2022.

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