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By NASA
5 min read
Percolating Clues: NASA Models New Way to Build Planetary Cores
NASA’s Perseverance rover was traveling in the channel of an ancient river, Neretva Vallis, when it captured this view of an area of scientific interest nicknamed “Bright Angel” – the light-toned area in the distance at right. The area features light-toned rocky outcrops that may represent either ancient sediment that later filled the channel or possibly much older rock that was subsequently exposed by river erosion. NASA/JPL-Caltech A new NASA study reveals a surprising way planetary cores may have formed—one 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 NASA’s 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 core—even before a planet’s 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 scenario—especially 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 street—it 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 didn’t 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 imagery—confirming long-standing models about how core formation can occur through percolation, in which dense liquid sulfide travels through microscopic cracks in solid rock.
“We could actually see in full 3D renderings how the sulfide melts were moving through the experimental sample, percolating in cracks between other minerals,” said Dr. Sam Crossley of the University of Arizona in Tucson, who led the project while a postdoctoral fellow with NASA Johnson’s ARES Division. “It confirmed our hypothesis—that 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.”
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 samples—or “run products”—were brought to NASA Johnson’s X-ray computed tomography (XCT) lab for imaging.
A molten sulfide network (colored gold) percolates between silicate mineral grains in this cut-out of an XCT rendering—rendered are unmelted silicates in gray and sulfides in white. Credit: Crossley et al. 2025, Nature Communications X-ray scientist and study co-author Dr. Scott Eckley of Amentum at NASA Johnson used XCT to produce high-resolution 3D renderings—revealing 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.
“We took the next step and searched for forensic chemical evidence of sulfide percolation in meteorites,” Crossley said. “By partially melting synthetic sulfides infused with trace platinum-group metals, we were able to reproduce the same unusual chemical patterns found in oxygen-rich meteorites—providing strong evidence that sulfide percolation occurred under those conditions in the early solar system.”
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.
“Working on this project pushed us to be creative,” Setera said. “To 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.”
When paired with Setera’s 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.
Dr. Sam Crossley welds shut the glass tube of the experimental assembly. To prevent reaction with the atmosphere and precisely control oxygen and sulfur content, experiments needed to be sealed in a closed system under vacuum. Credit: Amentum/Dr. Brendan Anzures The study offers a new lens through which to interpret planetary geochemistry. Mars in particular shows signs of early core formation—but the timeline has puzzled scientists for years. The new results suggest that Mars’ core may have formed at an earlier stage, thanks to its sulfur-rich composition—potentially without requiring the full-scale melting that Earth experienced. This could help explain longstanding puzzles in Mars’ 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 planet’s formation, certain elements may behave differently than expected—remaining in the mantle instead of the core and affecting the geochemical “clocks” used to estimate planetary timelines.
This research advances our understanding of how planetary interiors can form under different chemical conditions—offering 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 Fellow—a program that recognizes outstanding early-career scientists within five years of earning their doctorate. Jointly offered by NASA’s 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 NASA’s ARES division, visit: https://ares.jsc.nasa.gov/
Victoria Segovia
NASA’s Johnson Space Center
281-483-5111
victoria.segovia@nasa.gov
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Last Updated May 22, 2025 Related Terms
Astromaterials Planetary Science Planetary Science Division The Solar System Explore More
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By NASA
NASA and the Sam Houston Area Council (SHAC) of Scouting America signed a collaborative Space Act Agreement on December 17, 2024, expanding youth access to programs and opportunities with the Johnson Space Center’s Office of STEM Engagement (OSTEM) in Houston.
The agreement forges the first formal partnership between NASA OSTEM and Scouting America. It will leverage NASA’s educational outreach programs to enrich scout activities and experiences while providing the agency with new opportunities to engage youth around its mission, vision, and goals.
NASA Acting Associate Administrator Vanessa Wyche (left), at the time serving as director of Johnson Space Center, and Sam Houston Area Council of Scouting America Executive Officer Marvin Smith sign a Space Act Agreement on Dec. 17, 2024. NASA/James Blair “Our ability to explore the unknown and innovate for the benefit of all humanity depends on a highly skilled and competitive STEM workforce,” said NASA Acting Associate Administrator Vanessa Wyche. “Together with SHAC, we can inspire future generations of explorers, scientists, and engineers to help us take the next giant leap toward exciting discoveries.”
The agreement has already enabled NASA and SHAC to collaborate on a new space-focused summer experience at Camp Strake, the council’s premier camping facility in Southeast Texas. During the weeklong program, scouts will participate in hands-on STEM activities created in partnership with NASA, tour Johnson Space Center, attend robotics and space exploration workshops, and get an in-depth look at NASA’s current projects. SHAC serves approximately 25,000 youth in 16 counties in Southeast Texas.
Wyche and Johnson leadership presented Smith and members of local scout troops with an American flag that flew aboard NASA’s SpaceX Crew-8 mission. NASA/James Blair “NASA and SHAC share common goals of growing youth interest in science, technology, engineering, and math careers, and providing access to programs and experiences that prepare them to enter the STEM workforce,” said Gamaliel Cherry, director of Johnson’s Office of STEM Engagement. “We are excited to connect more students to NASA’s mission, work, and people through this partnership.”
NASA OSTEM provides opportunities for the next generation of explorers to discover and hone the science, technology, engineering, and math skills needed for the agency’s bold exploration plans.
For the latest NASA STEM events, news, and activities for students at any grade level, visit:
https://stem.nasa.gov
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By NASA
5 Min Read Planetary Alignment Provides NASA Rare Opportunity to Study Uranus
Artist's illustration showing a distant star going out of sight as it is eclipsed by Uranus – an event known as a planetary stellar occultation. Credits: NASA/Advanced Concepts Laboratory When a planet’s orbit brings it between Earth and a distant star, it’s more than just a cosmic game of hide and seek. It’s an opportunity for NASA to improve its understanding of that planet’s atmosphere and rings. Planetary scientists call it a stellar occultation and that’s exactly what happened with Uranus on April 7.
Observing the alignment allows NASA scientists to measure the temperatures and composition of Uranus’ stratosphere – the middle layer of a planet’s atmosphere – and determine how it has changed over the last 30 years since Uranus’ last significant occultation.
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This rendering demonstrates what is happening during a stellar occultation and illustrates an example of the light curve data graph recorded by scientists that enables them to gather atmospheric measurements, like temperature and pressure, from Uranus as the amount of starlight changes when the planet eclipses the star.NASA/Advanced Concepts Laboratory “Uranus passed in front of a star that is about 400 light years from Earth,” said William Saunders, planetary scientist at NASA’s Langley Research Center in Hampton, Virginia, and science principal investigator and analysis lead, for what NASA’s team calls the Uranus Stellar Occultation Campaign 2025. “As Uranus began to occult the star, the planet’s atmosphere refracted the starlight, causing the star to appear to gradually dim before being blocked completely. The reverse happened at the end of the occultation, making what we call a light curve. By observing the occultation from many large telescopes, we are able to measure the light curve and determine Uranus’ atmospheric properties at many altitude layers.”
We are able to measure the light curve and determine Uranus' atmospheric properties at many altitude layers.
William Saunders
Planetary Scientist at NASA's Langley Research Center
This data mainly consists of temperature, density, and pressure of the stratosphere. Analyzing the data will help researchers understand how the middle atmosphere of Uranus works and could help enable future Uranus exploration efforts.
To observe the rare event, which lasted about an hour and was only visible from Western North America, planetary scientists at NASA Langley led an international team of over 30 astronomers using 18 professional observatories.
Kunio Sayanagi, NASA’s principal investigator for the Uranus Stellar Occultation Campaign 2025, meeting virtually with partners and observing data from the Flight Mission Support Center at NASA’s Langley Research Center in Hampton, Virginia during Uranus’ stellar occultation event on April 7, 2025.NASA/Dave MacDonnell “This was the first time we have collaborated on this scale for an occultation,” said Saunders. “I am extremely grateful to each member of the team and each observatory for taking part in this extraordinary event. NASA will use the observations of Uranus to determine how energy moves around the atmosphere and what causes the upper layers to be inexplicably hot. Others will use the data to measure Uranus’ rings, its atmospheric turbulence, and its precise orbit around the Sun.”
Knowing the location and orbit of Uranus is not as simple as it sounds. In 1986, NASA’s Voyager 2 spacecraft became the first and only spacecraft to fly past the planet – 10 years before the last bright stellar occultation occured in 1996. And, Uranus’ exact position in space is only accurate to within about 100 miles, which makes analyzing this new atmospheric data crucial to future NASA exploration of the ice giant.
These investigations were possible because the large number of partners provided many unique views of the stellar occultation from many different instruments.
NASA planetary scientist William Saunders and Texas A&M University research assistant Erika Cook in the control room of the McDonald Observatory’s Otto Struve Telescope in Jeff Davis County, Texas, during the Uranus stellar occultation on April 7, 2025.Joshua Santana Emma Dahl, a postdoctoral scholar at Caltech in Pasadena, California, assisted in gathering observations from NASA’s Infrared Telescope Facility (IRTF) on the summit of Mauna Kea in Hawaii – an observatory first built to support NASA’s Voyager missions.
“As scientists, we do our best work when we collaborate. This was a team effort between NASA scientists, academic researchers, and amateur astronomers,” said Dahl. “The atmospheres of the gas and ice giant planets [Jupiter, Saturn, Uranus, and Neptune] are exceptional atmospheric laboratories because they don’t have solid surfaces. This allows us to study cloud formation, storms, and wind patterns without the extra variables and effects a surface produces, which can complicate simulations very quickly.”
On November 12, 2024, NASA Langley researchers and collaborators were able to do a test run to prepare for the April occultation. Langley coordinated two telescopes in Japan and one in Thailand to observe a dimmer Uranus stellar occultation only visible from Asia. As a result, these observers learned how to calibrate their instruments to observe stellar occultations, and NASA was able to test its theory that multiple observatories working together could capture Uranus’ big event in April.
Researchers from the Paris Observatory and Space Science Institute, in contact with NASA, also coordinated observations of the November 2024 occultation from two telescopes in India. These observations of Uranus and its rings allowed the researchers, who were also members of the April 7 occultation team, to improve the predictions about the timing on April 7 down to the second and also improved modeling to update Uranus’ expected location during the occultation by 125 miles.
This image of Uranus from NIRCam (Near-Infrared Camera) on NASA’s James Webb Space Telescope exquisitely captures Uranus’s seasonal north polar cap and dim inner and outer rings. This Webb image also shows 9 of the planet’s 27 moons – clockwise starting at 2 o’clock, they are: Rosalind, Puck, Belinda, Desdemona, Cressida, Bianca, Portia, Juliet, and Perdita.NASA, ESA, CSA, STScI Uranus is almost 2 billion miles away from Earth and has an atmosphere composed of primarily hydrogen and helium. It does not have a solid surface, but rather a soft surface made of water, ammonia, and methane. It’s called an ice giant because its interior contains an abundance of these swirling fluids that have relatively low freezing points. And, while Saturn is the most well-known planet for having rings, Uranus has 13 known rings composed of ice and dust.
Over the next six years, Uranus will occult several dimmer stars. NASA hopes to gather airborne and possibly space-based measurements of the next bright Uranus occultation in 2031, which will be of an even brighter star than the one observed in April.
For more information on NASA’s Uranus Stellar Occultation Campaign 2025:
https://science.larc.nasa.gov/URANUS2025
Karen Fox / Molly Wasser
Headquarters, Washington
202-358-1600
karen.c.fox@nasa.gov / molly.l.wasser@nasa.gov
Charles Hatfield
Langley Research Center, Hampton, Virginia
757-262-8289
charles.g.hatfield@nasa.gov
About the Author
Charles G. Hatfield
Science Public Affairs Officer, NASA Langley Research Center
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Last Updated Apr 22, 2025 Related Terms
General Ice Giants Langley Research Center Planetary Science Division Uranus Explore More
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By NASA
NASA astronaut Nichole Ayers works at the controls of the robotics workstation in the International Space Station’s Destiny Laboratory. Credit: NASA Students from Woodland Park, Colorado, will connect with NASA astronaut Nichole Ayers as she answers prerecorded science, technology, engineering, and mathematics-related questions from aboard the International Space Station.
Watch the 20-minute space-to-Earth call at 11:55 a.m. EDT on Monday, April 21, on the NASA STEM YouTube Channel.
The event, hosted by Woodland Park High School, also is open to students from Woodland Park Middle School. The Colorado high school wants to show students that even though they reside in a small town, they can achieve big dreams. Ayers, who considers Colorado Springs and Divide, Colorado, home, is a graduate of Woodland Park.
Media interested in covering the event must RSVP by 5 p.m., Friday, April 18 to Lindsey Prahl at lprah@wpsdk12.org or 719-922-1019.
For more than 24 years, astronauts have continuously lived and worked aboard the space station, testing technologies, performing science, and developing skills needed to explore farther from Earth. Astronauts aboard the orbiting laboratory communicate with NASA’s Mission Control Center in Houston 24 hours a day through SCaN’s (Space Communications and Navigation) Near Space Network.
Important research and technology investigations taking place aboard the space station benefit people on Earth and lays the groundwork for other agency missions. As part of NASA’s Artemis campaign, the agency will send astronauts to the Moon to prepare for future human exploration of Mars; inspiring Artemis Generation explorers and ensuring the United States continues to lead in space exploration and discovery.
See videos and lesson plans highlighting space station research at:
https://www.nasa.gov/stemonstation
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Tiernan Doyle
Headquarters, Washington
202-358-1600
tiernan.doyle@nasa.gov
Sandra Jones
Johnson Space Center, Houston
281-483-5111
sandra.p.jones@nasa.gov
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Last Updated Apr 17, 2025 LocationNASA Headquarters Related Terms
Astronauts Humans in Space International Space Station (ISS) ISS Research Johnson Space Center Nichole Ayers STEM Engagement at NASA View the full article
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