Percolating Clues: NASA Models New Way to Build Planetary Cores
- NASA has discovered a new way planetary cores may have formed, challenging the long-held belief that large-scale melting was necessary for core formation.
- The study suggests that molten sulfide could percolate through solid rock and form a core, even before a planet’s silicate mantle begins to melt, which is especially relevant for planets forming farther from the Sun.
- Researchers used high-resolution 3D imagery and geochemical analysis to confirm that molten sulfide had migrated and coalesced within a solid planetary interior, marking the first direct demonstration of this process in a laboratory setting.
- The new findings offer a new lens through which to interpret planetary geochemistry, particularly for Mars, where early core formation has puzzled scientists for years, and may have formed at an earlier stage due to its sulfur-rich composition.
- The study’s results also raise questions about how scientists date core formation events using radiogenic isotopes, such as hafnium and tungsten, and highlight the importance of collaborative, multi-method approaches in uncovering processes that were once only theoretical.
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Percolating Clues: NASA Models New Way to Build Planetary Cores
A new NASA study reveals a surprising way planetary cores may have formedâone that could reshape how scientists understand the early evolution of rocky planets like Mars.
Conducted by a team of early-career scientists and long-time researchers across the Astromaterials Research and Exploration Science (ARES) Division at NASAâs Johnson Space Center in Houston, the study offers the first direct experimental and geochemical evidence that molten sulfide, rather than metal, could percolate through solid rock and form a coreâeven before a planetâs silicate mantle begins to melt.
For decades, scientists believed that forming a core required large-scale melting of a planetary body, followed by heavy metallic elements sinking to the center. This study introduces a new scenarioâespecially relevant for planets forming farther from the Sun, where sulfur and oxygen are more abundant than iron. In these volatile-rich environments, sulfur behaves like road salt on an icy streetâit lowers the melting point by reacting with metallic iron to form iron-sulfide so that it may migrate and combine into a core. Until now, scientists didnât know if sulfide could travel through solid rock under realistic planet formation conditions.
Working on this project pushed us to be creative. It was exciting to see both data streams converge on the same story.
Dr. Jake Setera
ARES Scientist with Amentum
The study results gave researchers a way to directly observe this process using high-resolution 3D imageryâconfirming long-standing models about how core formation can occur through percolation, in which dense liquid sulfide travels through microscopic cracks in solid rock.
âWe could actually see in full 3D renderings how the sulfide melts were moving through the experimental sample, percolating in cracks between other minerals,â said Dr. Sam Crossley of the University of Arizona in Tucson, who led the project while a postdoctoral fellow with NASA Johnsonâs ARES Division. âIt confirmed our hypothesisâthat in a planetary setting, these dense melts would migrate to the center of a body and form a core, even before the surrounding rock began to melt.â
Recreating planetary formation conditions in the lab required not only experimental precision but also close collaboration among early-career scientists across ARES to develop new ways of observing and analyzing the results. The high-temperature experiments were first conducted in the experimental petrology lab, after which the resulting samplesâor ârun productsââwere brought to NASA Johnsonâs X-ray computed tomography (XCT) lab for imaging.
X-ray scientist and study co-author Dr. Scott Eckley of Amentum at NASA Johnson used XCT to produce high-resolution 3D renderingsârevealing melt pockets and flow pathways within the samples in microscopic detail. These visualizations offered insight into the physical behavior of materials during early core formation without destroying the sample.
The 3D XCT visualizations initially confirmed that sulfide melts could percolate through solid rock under experimental conditions, but that alone could not confirm whether percolative core formation occurred over 4.5 billion years ago. For that, researchers turned to meteorites.
âWe took the next step and searched for forensic chemical evidence of sulfide percolation in meteorites,â Crossley said. âBy partially melting synthetic sulfides infused with trace platinum-group metals, we were able to reproduce the same unusual chemical patterns found in oxygen-rich meteoritesâproviding strong evidence that sulfide percolation occurred under those conditions in the early solar system.â
To understand the distribution of trace elements, study co-author Dr. Jake Setera, also of Amentum, developed a novel laser ablation technique to accurately measure platinum-group metals, which concentrate in sulfides and metals.
âWorking on this project pushed us to be creative,â Setera said. âTo confirm what the 3D visualizations were showing us, we needed to develop an appropriate laser ablation method that could trace the platinum group-elements in these complex experimental samples. It was exciting to see both data streams converge on the same story.â
When paired with Seteraâs geochemical analysis, the data provided powerful, independent lines of evidence that molten sulfide had migrated and coalesced within a solid planetary interior. This dual confirmation marked the first direct demonstration of the process in a laboratory setting.
The study offers a new lens through which to interpret planetary geochemistry. Mars in particular shows signs of early core formationâbut the timeline has puzzled scientists for years. The new results suggest that Marsâ core may have formed at an earlier stage, thanks to its sulfur-rich compositionâpotentially without requiring the full-scale melting that Earth experienced. This could help explain longstanding puzzles in Marsâ geochemical timeline and early differentiation.
The results also raise new questions about how scientists date core formation events using radiogenic isotopes, such as hafnium and tungsten. If sulfur and oxygen are more abundant during a planetâs formation, certain elements may behave differently than expectedâremaining in the mantle instead of the core and affecting the geochemical âclocksâ used to estimate planetary timelines.
This research advances our understanding of how planetary interiors can form under different chemical conditionsâoffering new possibilities for interpreting the evolution of rocky bodies like Mars. By combining experimental petrology, geochemical analysis, and 3D imaging, the team demonstrated how collaborative, multi-method approaches can uncover processes that were once only theoretical.
Crossley led the research during his time as a McKay Postdoctoral Fellowâa program that recognizes outstanding early-career scientists within five years of earning their doctorate. Jointly offered by NASAâs ARES Division and the Lunar and Planetary Institute in Houston, the fellowship supports innovative research in astromaterials science, including the origin and evolution of planetary bodies across the solar system.
As NASA prepares for future missions to the Moon, Mars, and beyond, understanding how planetary interiors form is more important than ever. Studies like this one help scientists interpret remote data from spacecraft, analyze returned samples, and build better models of how our solar system came to be.
For more information on NASAâs ARES division, visit: https://ares.jsc.nasa.gov/
Victoria Segovia
NASAâs Johnson Space Center
281-483-5111
victoria.segovia@nasa.gov
