Recent investigations conducted at Rice University indicate that sulfur plays a pivotal role in maintaining Mercury’s internal molten state at reduced temperatures, thereby illuminating the evolutionary pathways of the planet’s distinctive crust and mantle.
Yishen Zhang & Rajdeep Dasgupta offer novel perspectives on the influence of sulfur in governing the thermochemical development of Mercury and analogous reduced rocky planetary systems. Image attribution: NASA / Johns Hopkins University Applied Physics Laboratory / Carnegie Institution of Washington.
“The superficial characteristics of Mercury stand in stark contrast to those of Earth,” remarked Professor Rajdeep Dasgupta, who directs the Rice Space Institute Center for Planetary Origins to Habitability.
“Our comprehension of Earth’s magmatic evolution proved insufficient for studying Mercury’s, and the data procured from exploratory missions remain challenging to interpret.”
“Consequently, we devised methodologies to simulate the planet’s conditions within our laboratory environment—specifically, by utilizing the meteorite specimen known as Indarch.”
The Indarch meteorite, which experienced terrestrial impact in Azerbaijan in 1891, exhibits a striking resemblance to Mercury’s chemical composition.
Through the analysis of this meteorite, the research team elucidated how Mercury’s unique chemical constituents have shaped its planetary development, disseminating their findings in a recently published scholarly article.
“From a chemical standpoint, Indarch is as reduced as the rocky materials found on Mercury,” stated Yishen Zhang, a postdoctoral researcher affiliated with Rice University.
“It is presumed to be a potential constituent in the planet’s formation.”
Employing a model melt composition derived from Indarch, the scientists simulated the behavior of Mercury’s rocks under elevated pressure and temperature conditions within a specialized facility.
The experimental procedure was straightforward: the chemical components of Indarch were combined in a small glass vial, the facility’s parameters were adjusted to replicate Mercurian conditions, the chemicals were introduced, and the mixture was subjected to heating.
“This simulated rock-cooking process affords us insights into the chemical transformations occurring within Mercury,” Zhang explained.
“By leveraging temperature, pressure, and chemical constraints derived from spacecraft observations and theoretical models, we reproduce Mercury-like environments to comprehend magma generation and evolution on the planet, even in the absence of direct geological samples.”
The research demonstrated that sulfur significantly reduces the temperature at which these highly reduced molten rocks initiate crystallization.
This implies that magmas on Mercury, enriched in sulfur, may retain their molten state at lower temperatures compared to analogous magmas on Earth.
The substantial decrease in crystallization temperature is attributable to Mercury’s distinctive chemical makeup: a paucity of iron, an abundance of sulfur, and a chemically reduced state.
Sulfur exhibits a propensity for bonding with other elements, most notably iron.
In iron-rich celestial bodies like Mars and Earth, the majority of sulfur is chemically bound to iron. However, Mercury’s limited iron content compelled its sulfur to seek alternative bonding partners.
Specifically, sulfur was able to form bonds with principal rock-forming elements such as magnesium and calcium.
On Earth, these rock-forming elements typically associate with oxygen, creating a robust structural matrix known as a silicate network, which comprises silicon, oxygen, and these elements.
The substitution of oxygen by sulfur, however, weakens this network, leading to crystallization at a reduced temperature.
“Given that Indarch may represent Mercury’s primordial state, these experiments strongly suggest that Mercury likely formed with sulfur occupying a structural role that, on Earth, is fulfilled by oxygen. This fundamentally alters the solidification dynamics of the planet’s mantle,” Zhang elaborated.
“This offers a compelling perspective on how Mercury might have evolved into a planet with its current unique surface geochemistry,” stated Professor Dasgupta.
“More significantly, it provides a framework for conceptualizing planets not through the lens of Earth’s formation, but by considering their distinct chemistries and magmatic processes operating under vastly divergent conditions.”
“Just as water or carbon influences magmatic evolution on Earth, sulfur performs a comparable function on Mercury.”
The findings are presented in the esteemed journal Geochimica et Cosmochimica Acta.
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Yishen Zhang & Rajdeep Dasgupta. The effects of sulfur on near-liquidus phase relations of highly reduced basaltic melts with implications for magmatism in Mercury. Geochimica et Cosmochimica Acta, published online February 26, 2026; doi: 10.1016/j.gca.2026.02.034
