Deep beneath the surface of Mars and Earth, where pressures crush rock and temperatures soar past 2,000°C, a silent chemical drama may have shaped the fate of both planets. In the churning depths of ancient magma oceans, a mineral called majorite quietly locked away vast amounts of ferric iron—Fe³⁺—a discovery that’s rewriting how scientists understand planetary evolution. This isn’t just a detail for geologists; it’s a clue to why Earth developed an oxygen-rich atmosphere and whether Mars ever had the chemistry to support life.
The oxidation state of a planet’s mantle—the balance between reduced and oxidized iron—governs everything from volcanic gas emissions to the melting behavior of rock. For decades, researchers assumed that Fe³⁺ was scarce in high-pressure minerals like majorite, which forms between 500 and 600 kilometers deep in Earth’s mantle and at the base of Mars’s. But a breakthrough study led by Hideharu Kuwahara at Ehime University has shown otherwise. Using a multi-anvil apparatus capable of simulating conditions at 18 gigapascals—nearly 180,000 times Earth’s atmospheric pressure—his team synthesized majorite from molten rock at 2,150–2,200°C. Then, at Japan’s SPring-8 synchrotron facility, they used X-ray absorption spectroscopy to measure the iron chemistry with unprecedented precision.
The results were striking: majorite can hold far more Fe³⁺ than previously believed, second only to bridgmanite, the most abundant mineral in Earth’s lower mantle. This means that as the primordial magma oceans of Earth and Mars cooled and solidified, majorite acted like a chemical sponge, soaking up oxidized iron. Later, when these deep rocks rose toward the surface and transformed into other minerals, they likely released excess Fe³⁺, potentially triggering the formation of more oxidized magmas. Such magmas could have released gases like water vapor and carbon dioxide, gradually shaping early atmospheres.
The implications stretch across planets. On Mars, where the mantle is thought to have been more reducing, the presence of Fe³⁺-rich majorite suggests pockets of unexpected oxidation—possibly enough to influence volcanic outgassing and surface chemistry. On Earth, this process may have helped set the stage for a planet where life could eventually thrive. As scientists refine models of planetary formation, this discovery adds a critical constraint: oxidation didn’t just happen at the surface. It was baked into the deep mantle from the very beginning.
Now, as missions to Mars return more data and new telescopes probe rocky exoplanets, understanding the hidden chemistry of minerals like majorite could help us identify which worlds have the deep-seated potential for habitability.