A team of researchers analyzed the iron meteorite named "Campo del Cielo" which was found in Argentina. The meteorite displays a rare combination of two distinct iron-nickel alloys that crystallized in the core of the planetesimal that was the precursor of the meteorite.

“The oldest metallic meteorites are relics of some of the first solid objects in the Solar System,” explained lead-author Dr. Juan Carlos (Coco) Villac from the Institute of Astronomy and Space Physics in Buenos Aires and the Planetary Science Institute (PSI) in Tucson, Arizona.

The Campo del Cielo meteorite is composed mostly of kamacite, an iron-nickel alloy with a body-centered cubic atomic structure; and taenite, an iron-nickel alloy with a face-centered cubic structure.

Using electron microscopy techniques and X-ray diffraction measurements at the Advanced Photon Source at the Argonne National Laboratory in Illinois, the team found that its main metal constituent, kamacite, formed with two distinct compositions during a stage of slow cooling following the initial solidification of the planetesimal's core.

This shows that the metallic core underwent a complex crystallization process whereby part of the core solidified slowly enough for diffusion and exsolution to take place, allowing two different compositions of kamacite to form, whereas the other part solidified rapidly, preserving the initial bulk composition.

“This textural relationship is one-of-a-kind among all known iron meteorites,” added co-author Dr. Meenakshi Wadhwa from ASU's School of Earth and Space Exploration and PSI. “It provides evidence that the planetesimal that formed this meteorite experienced very different cooling rates as different regions of its core crystallized. Campo del Cielo is clearly sampling a unique part of the parent body.”