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Why might potassium form an alloy with iron under the extreme pressure of Earth’s core?

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A color-coded periodic table of the elements displays each element's symbol and atomic number, with categories such as alkali metals, noble gases, halogens, transition metals, and actinoid elements distinguished by different background colors. — alkali metal Modern version of the periodic table of the elements (printable).

Under the extreme pressures found in Earth’s core, potassium undergoes a phase transition that alters its fundamental electronic structure. At these pressures, which can reach half a million atmospheres or more, the valence electrons of potassium shift from occupying a large s-type orbital to a d-type orbital.1

This transition causes potassium to behave more like a transition metal rather than a typical alkali metal. As a result of this change, the atomic volume of potassium becomes similar to that of transition metals like iron, allowing the two elements to form an alloy. Scientists have proposed that the formation of such a potassium-iron alloy under these extreme conditions may explain why the density of Earth’s core is lower than what would otherwise be expected.12