New research from Rice University reveals that sulfur plays a crucial role in maintaining the cool, molten interior of Mercury, offering fresh insights into the evolution of the planet’s unique crust and mantle.
Yishen Zhang and Rajdeep Dasgupta shed light on sulfur’s influence in shaping the thermochemical evolution of Mercury and similar reduced rocky planets. Image credit: NASA / Johns Hopkins University Applied Physics Laboratory / Carnegie Institution of Washington.
“Mercury’s surface is distinctly different from Earth’s,” explains Rajdeep Dasgupta, director of the Center for Planetary Origins and Habitability at the Rice Institute for Space Studies.
“Relying on Earth-based assumptions to study Mercury’s igneous evolution is inadequate, and mission data presents interpretation challenges.”
“We needed a way to replicate Mercury’s conditions in the lab using a meteorite known as Indarch.”
The Indarch meteorite, which fell in Azerbaijan in 1891, mirrors Mercury’s chemical composition closely.
Researchers leveraged the similarities with Indarch to investigate Mercury’s formation, publishing their findings in a recent paper.
“Indarch is chemically as reduced as Mercury’s rocks,” stated Yishen Zhang, a postdoctoral fellow at Rice University.
“It may even provide clues regarding Earth’s building blocks.”
Using the model melt composition from Indarch, scientists created a synthetic version of Mercury rock in a high-pressure, high-temperature environment.
The procedure was quite straightforward: they combined Indarch’s chemical components in small glass vessels, adjusted the facility to mimic Mercury’s conditions, added chemicals, and initiated the cooking process.
“This rock-cooking technique reveals the chemical processes occurring within Mercury,” Zhang remarked.
“By employing temperature, pressure, and chemical parameters derived from spacecraft observations, we aim to recreate Mercury-like conditions to enhance our understanding of magma formation and evolution—even without direct samples from the planet.”
The researchers discovered that sulfur reduces the temperature at which these molten, reduced rocks crystallize.
This indicates that Mercury’s sulfur-rich magma remains molten at lower temperatures compared to Earth’s similar magma.
The significant drop in crystallization temperature is attributed to Mercury’s unique chemical profile: low iron, high sulfur, and its chemically reduced state.
Sulfur is a versatile element, typically bonding with other elements, predominantly iron.
In iron-rich planets like Mars and Earth, sulfur is mostly attached to iron. However, Mercury’s low iron content allows sulfur to seek out new partners.
Specifically, sulfur can bond with key rock-forming elements such as magnesium and calcium.
On Earth, these rock-forming elements typically combine with oxygen to form stable structures known as silicate networks, made up of silicon, oxygen, and these elements.
Nonetheless, when sulfur replaces oxygen in this network, the structure becomes weaker, leading to lower crystallization temperatures.
“Since Indarch may represent a protoplanetary state of Mercury, our experiments suggest that sulfur likely occupied a structural role typically held by oxygen on Earth. This fundamentally alters the crystallization behavior of Mercury’s mantle,” noted Zhang.
“This provides fascinating insights into Mercury’s evolution and the distinct chemistry of its surface,” remarked Professor Dasgupta.
“More critically, it enables us to consider planetary formation in terms of their unique chemistries and igneous dynamics under various conditions.”
“Sulfur influences Mercury similarly to how water and carbon influence magma evolution on Earth.”
The findings are published in the journal Geochimica et Cosmochimica Acta.
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Yishen Zhang and Rajdeep Dasgupta. Effects of sulfur on the near-liquid phase relationships of highly reduced basaltic melts and implications for Mercury’s magmatism. Geochimica et Cosmochimica Acta published online on February 26, 2026. doi: 10.1016/j.gca.2026.02.034
Source: www.sci.news
