Sulfur-rich magma on Mercury remains liquid at temperatures far lower than similar materials on Earth, a discovery that challenges existing models of how the solar system’s innermost planet formed. Researchers at Rice University found that this chemical quirk allowed Mercury’s interior to stay molten longer, fundamentally altering the evolution of its crust and mantle.
Rice University researchers simulated Mercury’s interior using a 19th-century meteorite
Scientists don’t have direct samples from Mercury’s surface. To bridge this gap, Rajdeep Dasgupta and his team used the Indarch meteorite, a space rock that landed in Azerbaijan in 1891. The meteorite’s chemical composition closely mirrors that of Mercury, specifically its “reduced” state where substances have gained electrons.
Yishen Zhang, a postdoctoral researcher and the study’s lead author, used Indarch as a blueprint to “cook” synthetic Mercury rocks. The team mixed the meteorite’s chemical ingredients in small glass vials and subjected them to extreme heat and pressure in a specialized facility to replicate the planet’s internal environment.
This lab-based approach was necessary as spacecraft data alone are difficult to interpret. By recreating these conditions, the team could observe how magma behaves in an environment with almost no oxygen but massive amounts of sulfur.
Why low iron levels forced sulfur to find new binding partners
Sulfur is a “promiscuous” element that typically binds to iron on iron-rich planets like Earth and Mars. Because Mercury is iron-poor, its sulfur had to find different elements to bond with to achieve stability.
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The Rice team discovered that sulfur on Mercury binds to major rock-forming elements, specifically magnesium and calcium. On Earth, these same elements typically bind with oxygen to create a stable silicate network.
On Mercury, sulfur essentially replaces oxygen in the molecular structure. This substitution creates a fundamentally different chemical environment than anything seen on Earth.
From oxygen replacement to delayed crystallization
The bond between sulfur and rock-forming elements is weaker than the bond formed with oxygen. This structural weakness leads to a significantly lower melting point for the planet’s rocks.
Because the melting point is lower, the magma stays molten at temperatures where Earth-like magma would have already solidified. This delayed crystallization means the process of the mantle solidifying happened in a way never before seen in the solar system.
These conditions explain why Mercury possesses such a unique, iron-poor crust. The sulfur-driven chemistry reshaped the interior evolution of the planet over billions of years.
Earth-based geologic models don’t apply to the most reduced planet
Planetary science often relies on Earth as a baseline for understanding neighbors like Venus and Mars. This research proves that such assumptions fail when applied to the solar system’s most reduced planet.
This follows our earlier report, Yellowstone Supervolcano: New Study Reveals Shallow Magma Source and Tectonic Forces.
Sulfur acts as the primary driver for Mercury’s magmatic evolution, performing the role that water and carbon play for Earth. The findings, published in Geochimica et Cosmochimica Acta, suggest that a planet’s specific mineral ratios and reduced state can create entirely different geologic cycles.
This new framework allows researchers to view planetary formation through a different lens. It suggests that other similarly reduced rocky planetary systems across the universe may follow these same sulfur-dominant rules rather than the oxygen-dominant rules of Earth.
Why was the Indarch meteorite essential for this study?
The Indarch meteorite is chemically “reduced,” meaning its substances have gained electrons, which matches the unique chemical state of Mercury. Since scientists lack direct samples from the planet’s surface, the meteorite provided a viable chemical proxy to simulate Mercury’s interior in a lab.
How does sulfur change the way Mercury’s magma behaves?
Because Mercury is iron-poor, sulfur binds to magnesium and calcium instead of iron. This replaces oxygen in the molecular structure and creates weaker silicate networks, which lowers the melting point and allows magma to remain liquid at lower temperatures than it would on Earth.
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