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Rice University researchers have found that Mercury’s low-iron, high-sulfur chemistry allows its magma to stay liquid at lower temperatures than Earth’s
By using a rare meteorite to simulate Mercury’s interior, they discovered that sulfur essentially replaces oxygen in the planet’s molecular structure, completely changing how its crust and mantle evolved.
Published in Geochimica et Cosmochimica Acta, the study explains why the solar system’s smallest planet has such a unique, iron-poor crust.
Recreating mercury in a lab
Because scientists lack direct samples from Mercury’s surface, Rajdeep Dasgupta and his team turned to the Indarch meteorite. This rare space rock, which fell in Azerbaijan in 1891, is chemically “reduced” (meaning its substances have gained electrons), matching the unique chemical state of Mercury.
Using the Indarch meteorite as a blueprint, lead author Yishen Zhang recreated the high-pressure, high-temperature conditions of Mercury’s interior. By mixing the meteorite’s chemical ingredients and “cooking” them, the researchers could observe how magma behaves in an environment with almost no oxygen but massive amounts of sulfur.
The “promiscuous” role of sulfur
On Earth and Mars, sulfur usually binds to iron. However, Mercury is iron-poor, forcing sulfur to find new “binding partners.” The researchers found that on Mercury, sulfur binds to major rock-forming elements like magnesium and calcium.
On Earth, these elements would typically bind to oxygen to form a stable “silicate network.” On Mercury, sulfur takes oxygen’s place, which leads to significant structural changes:
Weakened silicate networks:
The bond between sulfur and rock-forming elements is weaker than the bond with oxygen.
Lowered melting point:
Delayed crystallization:
Because the magma remains liquid longer, the process of the planet’s mantle solidifying happened in a way never before seen in our solar system.
A new framework for planetary science
This discovery proves that researchers cannot use Earth-based assumptions to understand other worlds. Just as water and carbon dictate the “magmatic evolution” of Earth, sulfur is the primary driver for Mercury.
This research provides a new lens through which to view planetary formation. It suggests that a planet’s “reduced” state and specific mineral ratios can create entirely different geologic cycles, fundamentally changing how a planet’s crust and mantle form over billions of years.