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Ice can dissolve iron minerals more effectively than liquid water, according to a new study from Umeå University. The discovery could help explain why many Arctic rivers are now turning rusty orange as permafrost thaws in a warming climate.

On Greenland’s coast, glaciers meet the sea in narrow fjords that have been carved over hundreds of thousands of years. Ice cliffs tower hundreds of meters high.

At a glacier’s terminus, where those cliffs crash into the waters of the Atlantic, small (bus-sized) chunks of ice slough off all the time. Occasionally, a stadium-sized iceberg plunks into the water.

All this glacial calving impacts sea level rise and global climate, but there’s a lot that researchers don’t yet know about how calving happens. Now, scientists have gotten a detailed look at the whole process using a fiber-optic cable on the seafloor 500 meters from a glacier’s calving front. The findings were published last month in Nature.

Maneuvering Through the Mélange

Physical processes at the calving front control a glacier’s stability, said Dominik Gräff, a glaciologist at the University of Washington in Seattle who led the new work.

“We don’t have much idea what’s actually going on below the water.”

But gaining access to a glacier’s front can be difficult, and remote sensing methods are able to visualize only the tiny fraction of the ice mass that isn’t submerged. “We don’t have much idea what’s actually going on below the water,” Gräff said.

“It’s always impressive for people to get any observations near the glacier front,” agreed David Sutherland, a physical oceanographer at the University of Oregon in Eugene who did not contribute to the new paper. Researchers working at the front, he explained, risk losing expensive equipment and have to navigate the mélange, a closely packed mix of sea ice and icebergs.

This was the first time fiber-optic sensing was deployed at a calving front. Unlike other methods, such as remote sensing and the use of submerged seismometers, fiber-optic sensing can capture myriad events across a range of times. “It can just sense everything,” Sutherland said.

Gräff and his team dropped a 10-kilometer (6.2-mile) cable on the ocean bottom across the fjord of the Eqalorutsit Kangilliit Sermiat (EKaS) glacier in South Greenland. The maneuver was somewhat tricky. “If you go too slow, the ice mélange that you push open with your vessel [will close] quickly,” Gräff said. “And that prevents your cable from sinking down.”

Julia Schmale, an assistant professor at École Polytechnique Fédérale de Lausanne (left), and Manuela Köpfli, a University of Washington graduate student in Earth and space science, unspool fiber-optic cable from a large drum on the R/V Adolf Jensen, deploying it to the fjord bottom to record data. Credit: Dominik Gräff/University of Washington

Once the cable was in place, researchers were able to collect a wealth of data.

Waves, Wakes, and Cracking

Laser light pulsing through the fiber-optic cable allowed it to function like an entire network of sensors snaking across the fjord.

Acoustic vibrations associated with calving, for instance, stretched and compressed the cable and changed backscattered light signals. Measuring these changes is the basis for distributed acoustic sensing, or DAS.

In addition to measuring acoustics, fiber optics also allowed researchers to measure how light signals change because of temperature, a technique called distributed temperature sensing, or DTS. DAS and DTS allowed researchers to capture calving events that lasted mere milliseconds.

During the 3-week experiment at EKaS, the glass fiber captured 56,000 iceberg detachments.

(1) Initial cracking at EKaS was detected through an acoustic signature traveling through fjord waters. (2) Fractures eventually led to iceberg detachments that emitted seafloor-water interface waves. (3) Detachments caused calving-induced tsunamis at the water surface that caused changes in pressure along the fiber-optic cable. (4) Calving-induced internal gravity waves traveled between layers of fjord water with different temperatures and salinities. (5) Calved-off icebergs drifted away from the glacier terminus, dragging internal wave wakes behind them, agitating the stratified fjord waters and cooling the seafloor. (6) The internal wave wakes caused seafloor currents that generated vibrations in the cable through vortex shedding. (7) Finally, icebergs disintegrated by fracturing, again detected by fiber-optic sensing of acoustic signals. Credit: Gräff et al., 2025, https://doi.org/10.1038/s41586-025-09347-7, CC BY 4.0

That volume of observations meant researchers could trace the calving process from start to finish. It began as cracks formed in glacial ice. Sounds associated with the cracking traveled through the fjord and were picked up by the cable. Then icebergs detached from the glacier, creating underwater waves that traveled between the ice and the sediment below. Iceberg detachments also caused small, local tsunamis that could be identified by pressure changes on the cable at the bottom of the fjord.

In addition to tsunamis and surface waves, the fiber-optic cable was also able to detect internal gravity waves, which travel at the interface between an iceberg’s upper, cold layer of fresh water and the warmer layer of salty seawater below. The EKaS icebergs created wakes as they drifted from the glacier, dragging internal gravity waves behind them and causing circulation in the water. Researchers measured the resulting temperature changes using DTS.

Finally, the fiber-optic cable captured the sounds of icebergs disintegrating. These signals were similar to the initial sound of cracking in the glacier but instead came from the fjord.

Wealth of Data

“There are very few seismological datasets where, within such a short amount of time, you record so many different phenomena.”

“There are very few seismological datasets where, within such a short amount of time, you record so many different phenomena,” said Andreas Fichtner, a seismologist at ETH Zürich in Switzerland who was not part of the work but collaborates with one of the study’s authors. It takes detective work to decode all those signals and assign them to physical processes, he said. “It’s pretty remarkable.”

Gräff and the other researchers hope their rich datasets can improve glacial calving models, which often underestimate the melt that occurs below the surface. Sutherland said it’s not yet clear how to incorporate details from the study into such models, however. Researchers will need to connect the observed processes and the amount of ice lost to factors they can easily measure or estimate, such as ocean temperature and ice thickness, he explained. And they’ll need to study the calving process of different glaciers. EKaS sits on bedrock where it meets the sea, for instance, while other glaciers have a floating terminus.

Still, having a huge set of observations along with information about ocean conditions, which the researchers collected using a suite of other tools, “is pretty powerful,” Sutherland said. “Maybe we can start using this dataset to try to make predictions of when icebergs are going to calve.”

—Carolyn Wilke, Science Writer

Citation: Wilke, C. (2025), A fiber-optic cable eavesdrops on a calving glacier, Eos, 106, https://doi.org/10.1029/2025EO250351. Published on 22 September 2025. Text © 2025. The authors. CC BY-NC-ND 3.0
Except where otherwise noted, images are subject to copyright. Any reuse without express permission from the copyright owner is prohibited.

Author(s): N. R. Arista

A very basic aspect in the interaction of ions with plasmas is the effect of screening of the ion charge. In the case of classical plasmas this effect is usually described by linear theories. However, for dense quantum plasmas, deviations from the linear models arise and new effects appear. These no…

[Phys. Rev. E 112, 035210] Published Mon Sep 22, 2025

Earth's mantle is a restless, enigmatic engine that powers volcanism, recycles crust, and regulates the long-term evolution of the planet. But one of its most elusive characteristics—the redox state, or the balance of oxidized and reduced chemical species—remains difficult to measure directly.

Extremely heavy rainfall associated with super typhoon Ragasa could cause the Matai-an landslide dam to overtop in the next two days.

In East Asia, super typhoon Ragasa is moving westwards between Taiwan and the Philippines. At the time of writing, Earth Cut TV has a live feed from the Batanes Islands, almost in the path of the eye (although there is a good chance that data connectivity will be lost in the storm):-

This is an exceptional storm, bringing heavy rainfall and strong winds to a wide area.

The storm has the potential to bring extremely heavy rainfall to southern and eastern Taiwan. There is huge uncertainty as to the magnitude, but reports indicate that the Central Meteorological Administration has estimated that precipitation totals as high as 800 mm could be seen in the mountain areas of Hualien County.

As I have highlighted previously, there is a large valley-blocking landslide at Matai’an in Hualien County, with a large volume of water steadily accumulating. The image below, released by the Hualien Branch of the Forestry and Conservation Department, shows the level of the lake relative to the landslide dam:-

A recent photograph of the Matai’an landslide dam in Taiwan. Image from the Hualien Branch of the Forestry and Conservation Department.

As the image above shows, the freeboard is now quite low.

In consequence, the Forestry and Conservation Administration of the Ministry of Agriculture issued a red alert at 7 a.m. this morning (22 September), mandating the evacuation of vulnerable households downstream. It is estimated that this affects around 1,800 homes.

Should overtopping occur, it is anticipated that 24 September would be the most likely date, so we will need to watch with interest. The Central Weather Administration maintains an exceptional set of web resources recording accumulated precipitation in Taiwan.

Overtopping is not inevitable in the next few days, but that will almost certainly occur in the next few weeks. It is going to be fascinating to see what happens.

Return to The Landslide Blog homepage Text © 2023. The authors. CC BY-NC-ND 3.0
Except where otherwise noted, images are subject to copyright. Any reuse without express permission from the copyright owner is prohibited.

SummarySeismic surface wave tomography, particularly when leveraging dense array data, has become a widely used method for investigating shallow subsurface velocity structures. The shallow structures are usually characterized by rapid seismic velocity changes (i.e. seismic interfaces) due to variations in rock properties, sedimentary environments, or tectonic features. However, the commonly used grid-based parameterization of the velocity field in surface wave tomography often struggles to accurately constrain such interface geometries. In addition, traditional surface wave inversion methods typically rely on 1D inversion at individual stations using dispersion curves, followed by interpolation to construct 2D or 3D models. This approach can sometimes introduce spurious features and reduce model reliability. To address these limitations, we propose a geological and level-set parameterization approach for surface wave tomography, allowing for the explicit consideration of interface structures in inversion. This method is then combined with the Ensemble Kalman Inversion to optimize subsurface structures. Synthetic tests demonstrate that integrating 3D interface parameterization in tomography significantly enhances the reliability of the velocity model and the recovery of interface geometries. Applying this approach to the Woxi gold mine region in China yielded inversion results that closely align with existing borehole data. This study highlights the advantages of level-set parameterization for 3D interface imaging in seismic tomography, underscoring its potential in subsurface mineral exploration.

Satellite observations have documented a pronounced decline in Antarctic sea ice extent since 2014, with especially sharp losses in recent years. Whether Antarctica's declining sea ice can recover hinges not only on how much carbon dioxide we emit, but also on how stratified the Southern Ocean is, according to new research published in Geophysical Research Letters.

A new study has made a counterintuitive discovery about how El Niño affects India's summer monsoon. Instead of reducing rainfall overall and causing widespread droughts, the periodic climatic phenomenon increases rainfall daily in the country's wettest regions.

Craters formed by asteroid impacts are ubiquitous on rocky bodies, and our planet is no exception. Researchers believe they’ve pinpointed yet another impact crater on Earth, this one submerged beneath the North Sea. The structure, known as Silverpit Crater, was discovered roughly 2 decades ago, but its provenance has long been debated. With new subsurface imaging and rock samples, the team concluded that an impact produced Silverpit Crater roughly 45 million years ago. These results were published in Nature Communications.

“People simply didn’t believe it was an impact crater.”

Uisdean Nicholson, a geologist now at Heriot-Watt University in Edinburgh, Scotland, remembered the controversy that swirled around Silverpit Crater back in the late aughts. Was the circular feature lurking beneath the waters of the North Sea under roughly 700 meters of sediments caused by an asteroid impact, or something more plebeian like volcanism or subsidence?

Nicholson, a graduate student at the time, remembered the spirited discussion that ensued among scholars attending a Geological Society of London meeting in 2009. “It was a classic, old-school debate,” he said. The vote came out strongly in favor of a nonimpact origin.

“People simply didn’t believe it was an impact crater,” Nicholson said. It looked as though Silverpit Crater wasn’t destined to join the rarefied group of 200 or so confirmed impact structures on Earth.

Begging for Data

As Nicholson focused his research on other impact structures such as Nadir Crater, he kept thinking about Silverpit. One dataset in particular piqued his interest: a survey of the North Sea seafloor sediments collected in 2022. Those data, amassed on behalf of the Northern Endurance Partnership, a venture to explore carbon capture storage under the North Sea, afforded a close-up look at the 3-kilometer crater and its environs. Previous datasets had also imaged a similar area, but they were of lower resolution and did not cover the entire structure.

A colleague alerted Nicholson about the Northern Endurance Partnership data, and the researchers worked for several months to negotiate access to some of the proprietary observations. “I begged,” Nicholson said.

The researchers were ultimately successful in their quest, and the team pored over high-resolution seismic reflection data revealing faults and buried layers of sediments around Silverpit Crater. “The new data gives a far sharper set of images,” Nicholson said.

The fact that Silverpit Crater is so inaccessible is actually important scientifically, said Matthew S. Huber, a planetary scientist at the Planetary Science Institute in Tucson, Ariz., who was not involved in the research. “Because this crater formed in water and it was buried by sediments in the water immediately after it formed, the whole thing is preserved.”

Faults and Holes

The Northern Endurance Partnership data revealed faults consistent with rock being compacted to varying degrees, as would be expected in an impact. The observations also spotlighted several roughly 10-meter-deep and 250-meter-wide troughs near the rim of the crater. Such scarps could be features eroded by water rushing back into the crater after the impact, the team surmised.

In addition, Nicholson and his colleagues noticed a few pits located beyond the crater rim that were tens of meters deep and wide. “We see all these holes, essentially, around the crater for at least a crater diameter,” Nicholson said. The team thinks that such features are secondary craters, that is, structures formed by material lofted outward from the initial impact.

Secondary craters tend to be rare on Earth because they’re often rapidly erased by erosion after an impact. “We think this is the first really robust terrestrial evidence for secondary cratering,” Nicholson said.

Atomic Wrenching

In 1985, the company British Gas drilled an oil and gas well just a few kilometers northwest of Silverpit Crater. As part of the drilling process, debris excavated from the borehole was pumped to the surface, and some of it was retained for analysis. Nicholson and his colleagues obtained some of those sediments. On the basis of the appearance of tiny marine fossils in rocks from the same depth as Silverpit Crater, the team deduced that the feature formed roughly 43–46 million years ago.

Two mineral grains the team analyzed—one quartz and one feldspar, each roughly the diameter of a human hair—exhibited curious microscopic features. Both grains contained so-called planar deformation features, which are atomic rearrangements of the crystalline structure, Nicholson said. Such wrenching on an atomic scale is indicative of the extreme pressures associated with shock waves.

“This could wind up being a controversial paper within the impact community.”

A celestial object such as an asteroid or comet slamming into a rocky body can readily generate such pressures, but not much else can, Nicholson said. “It’s very difficult to form that any other way.”

The discovery of those shocked grains was a dead giveaway that Silverpit Crater formed from an impact, Nicholson and his colleagues proposed.

These results are convincing, Huber said, but a skeptic might rightfully have some questions. For instance, couldn’t the shocked grains have simply washed into the North Sea from another impact event? “They’ve only found one grain of quartz and one grain of feldspar,” Huber said. “This could wind up being a controversial paper within the impact community.”

—Katherine Kornei (@KatherineKornei), Science Writer

Citation: Kornei, K. (2025), Submerged crater near Europe tied to an impact, Eos, 106, https://doi.org/10.1029/2025EO250275. Published on 20 September 2025. Text © 2025. The authors. CC BY-NC-ND 3.0
Except where otherwise noted, images are subject to copyright. Any reuse without express permission from the copyright owner is prohibited.

Publication date: Available online 12 September 2025

Source: Advances in Space Research

Author(s): Shivam Kulshrestha, Sonali Bhatnagar, Surjeet Baghel

Deep in the heart of Central Asia, the Kunlun Mountains form a vital barrier on the northern Tibetan Plateau. Their rainfall is a lifeline, feeding the oases and rivers of the arid Tarim Basin. While scientists have mapped the region's basic climate patterns, one question remained: what drives the large year-to-year swings in summer rainfall here?

Earthquakes don't just shake the ground, they can also shift rivers, damage stop banks and raise the risk of flooding for years afterward.

Buried deep in Greenland's ice sheet lies a puzzling chemical signature that has sparked intense scientific debate. A sharp spike in platinum concentrations, discovered in an ice core (a cylinder of ice drilled out of ice sheets and glaciers) and dated to around 12,800 years ago, has provided support for a hypothesis that Earth was struck by an exotic meteorite or comet at that time.

On May 12, 2025, Buddha Day, Buddhist monks and scientific researchers gathered to pay tribute to Yala Glacier in Nepal's Langtang Valley. The International Center for Mountain Development (ICIMOD), an international NGO housed in Kathmandu, collaborated with local Indigenous community leaders to organize this event to raise awareness of Yala's rapid retreat and highlight the risk across Hindu Kush Himalayan (HKH) glaciers. They invited community leaders, local university professors and international media to the tribute, which included a central ceremony held by spiritual leaders.

An international research team led by the GEOMAR Helmholtz Center for Ocean Research Kiel has discovered a globally unique system on the seabed off the coast of Papua New Guinea. During their expedition aboard the research vessel SONNE, they came across the "Karambusel" field, where hydrothermal vents and methane seeps occur immediately adjacent to one another.

Hidden beneath the biggest ice mass on Earth, hundreds of subglacial lakes form a crucial part of Antarctica's icy structure, affecting the movement and stability of glaciers, and consequentially influencing global sea level rise.

Earlier in 2025, UNSW Sydney Ph.D. candidate Christina Schmidt submitted her thesis—from the deck of Australia's multi-billion-dollar icebreaker, just off the East Antarctic coast.

Every year, soils across Thailand are baked hard and bone-dry for months under the unrelenting tropical Sun. But once the long, hot buildup to the monsoon season comes to a head and the rains arrive—typically in May or June—the landscape transforms in a matter of weeks into a patchwork of verdant wetlands.

With this transformation comes a flurry of activity, because many of these wetlands are, in fact, rice paddies ready to be planted. Workers wade through the fields, scattering seed or planting seedlings one by one in the butter soft soil. Months later, as long as these plants have had adequate water and nutrients, they’ll be harvested for their all-important grains.

Rice paddies in Thailand and elsewhere are vital economically and for food security, with rice being the third-most-grown cereal commodity globally. They are also part of the worldwide system of wetlands. From rivers and lakes to marshlands and intertidal flats, wetlands are important ecological and geochemical systems because of the ecosystem services they provide: biodiversity, natural pollution remediation, carbon sequestration, and protection against storm surges, to name a few.

Worachart Wisawapipat of Kasetsart University checks the condition of the soil at a rice paddy experiment site in northeastern Thailand. Credit: Kurt Barmettler

Rice paddies are also of special interest to geochemists, because the regular seasonal pattern of flooding and drainage in many paddy fields makes them ideal natural laboratories in which to study soil biogeochemical processes. Indeed, in several locations in Thailand in 2021, scientists from the Swiss Federal Institute of Technology (ETH Zurich) and Kasetsart University in Bangkok joined the workers in the fields as the growing season began. The scientists were there to plant not rice, though, but iron minerals, with the purpose of testing a new method for investigating how cycles of wetting and drying contribute to these minerals’ reactivity in soil.

A Linchpin of Soil Functioning

Iron is a linchpin of chemical cycling in the environment.

Iron is usually among the most abundant elements in soils, and it is a linchpin of chemical cycling in the environment. It’s thus of critical interest to farmers concerned with the availability of nutrients to their plants, engineers determining risks posed by toxic elements in soil, and land managers wanting to understand soil carbon storage. For several reasons, iron more often than not significantly controls how soil nutrients and toxic elements behave, how carbon is stored, and how other chemical processes play out in soils.

One reason is that iron is reactive in a variety of environmental conditions. In contact with air, oxidized forms of iron—including the yellow-brown to orange oxyhydroxide minerals commonly recognized as rust—are most stable and abundant. When a soil is flooded and the flow of oxygen through it is restricted, some of these minerals may dissolve. This dissolution occurs because some microorganisms can use iron minerals as an alternative to oxygen in the reduction and oxidation (redox) reactions they rely on for energy. In other words, some microorganisms essentially breathe redox-active iron (see video below), reducing oxidized iron and converting it to other forms.

Iron is also very versatile and combines with many other chemical elements to form a wide variety of minerals such as oxyhydroxides, carbonates, phosphates, sulfides, hydroxysulfates, and others that can host trace elements in their structures. What’s more, iron mineral particles tend to be very small and have large surface areas that allow them to bind other compounds. This property also makes iron mineral particles susceptible to rapid change under evolving environmental conditions.

Following Mineral Transformations in Field Soils

Studying the behavior of iron in soils using measurement techniques that are not specific to iron is challenging. The relatively small signatures of iron minerals are often overshadowed by those of the much more abundant silicate minerals that make up the bulk of soil mass.

With techniques that do selectively detect iron in soil, such as synchrotron X-ray absorption spectroscopy, researchers can follow changes in the composition of a whole soil sample, but not changes in a single target mineral. And if the complexity of the surrounding soil is stripped away to perform simplified laboratory experiments focusing on iron minerals, the mineral transformations observed do not always reflect what happens in natural soils.

Katrin Schiedung of ETH Zurich takes soil samples in a flooded rice paddy in northeastern Thailand. Credit: Ruben Kretzschmar

Iron minerals enriched in iron-57 and having precisely controlled properties can be synthesized in the laboratory, then mixed into soils to undergo reactions similar to those of natural iron minerals.

To overcome the challenge of tracing iron mineral transformations in soil, we developed a new approach using a stable isotope of iron to label synthetic minerals. Iron-57 occurs naturally, making up about 2.1% of the iron in soils and exhibiting the same chemical behavior as other naturally occurring iron isotopes (iron-54, 5.8%; iron-56, 91.8%; iron-58, 0.3%). Iron minerals enriched in iron-57 and having precisely controlled properties can be synthesized in the laboratory, then mixed into soils to undergo reactions similar to those of natural iron minerals. Even if the experimental enrichment of iron in the soil is small, the iron-57 is predominantly present in the synthetic minerals, allowing us to focus specifically on what happens to those minerals.

We chose iron-57 as a tracer in our experiments because of the ability to analyze it using Mössbauer spectroscopy. This technique, based on Rudolf Mössbauer’s fortuitous (and 1961 Nobel Prize–winning) discovery of recoilless nuclear resonance fluorescence, is sensitive to the redox state and chemical environment around iron-57 atoms in a sample. Crucially, all other isotopes of iron are invisible using this technique.

Mössbauer spectroscopy has been widely used in the Earth sciences, including for mineralogical analyses of soil samples and Martian rocks. In our application, adding iron-57 minerals into soils and tracing them with Mössbauer spectroscopy allows us to follow otherwise hidden mineral transformations (Figure 1).

Fig. 1. In the newly developed method, iron-57-labeled (57Fe-labeled) synthetic minerals are used to enrich a natural soil sample, which is placed in a porous mesh bag so it can still interact chemically with the surrounding soil. Following the experiment, Mössbauer spectroscopy, which irradiates the sample with gamma rays of a frequency that interacts only with iron-57, is used to measure the transformation products of the labeled minerals.

After adding portions of synthetic jarosite (a potassium-iron hydroxysulfate) or ferrihydrite or lepidocrocite (both iron oxyhydroxides) to small plots in the Thai rice paddies early in the growing season, we went back several times until the end of the season 4 months later to collect soil samples for analysis.

The mineral transformations we observed with Mössbauer spectroscopy were dominated by the dissolution of the added minerals and the release of reduced iron into soil pore water. Proximity to bacteria in the soil promoted mineral dissolution, and some of the released iron either remained dissolved or was trapped on soil particles. New minerals that formed—including green rust, a highly reactive hydroxide mineral that is usually difficult to detect in the environment—tended to be nanocrystalline in size and often contained both reduced and oxidized forms of iron.

Joëlle Kubeneck of ETH Zurich removes a sediment core from the intertidal wetlands of Germany’s Wadden Sea. Credit: Ruben Kretzschmar

Such results can shed light on biogeochemical cycling that affects ecosystem processes. Dissolution of iron minerals might lead to releases of associated pollutants, nutrients, or carbon compounds, for example. On the other hand, we observed that many of the reaction products in soil are nanocrystalline minerals, which have large reactive surface areas that might adsorb dissolved compounds such as metals.

We have also applied this new approach to understand a range of iron mineral transformation processes in soil and sediment environments other than rice paddies. In sediments along Germany’s north coast, for example, we observed the in situ formation of vivianite, a reduced iron phosphate mineral, in a matter of weeks. Phosphorus in vivianite has limited bioavailability, so formation of the mineral can control the availability of phosphorus in the environment and potentially reduce the risk of eutrophication. In addition, we have used the method to study oxidation reactions of reduced iron minerals, sulfidization of vivianite and lepidocrocite leading to the formation of iron sulfide minerals like greigite, and interactions between iron and organic matter during redox cycles.

An Array of Applications

Iron minerals are ubiquitous in natural environments and are used in many engineering applications. We anticipate that iron-57 labeling of minerals coupled with Mössbauer spectroscopy, although applied only to soils so far, could help to answer questions about transformations of these minerals in other domains of the Earth sciences and beyond.

Using iron-57 tracers could contribute to studies on the origins of iron mineral assemblages in sedimentary deposits on Earth or other astronomical bodies such as Mars.

Using iron-57 tracers could, for example, contribute to studies on geological processes, including weathering or metamorphism, or on the origins of iron mineral assemblages in paleosols and other sedimentary deposits on Earth or other astronomical bodies such as Mars.

Experiments with iron-57-labeled minerals could also help to understand redox-driven iron mineral transformation processes at work in applied geoscience technologies. In pollution management, for example, permeable reactive barriers containing iron are a tool for mitigating the spread of contaminants in groundwater. Another example involves geological deposits of redox-active iron minerals that may be used to store or produce hydrogen as a clean energy source.

Outside the Earth sciences, potential applications of iron-57-labeled synthetic minerals exist in fields as diverse as corrosion science, construction engineering, and experimental archaeology. The formation of rust on iron-bearing objects is the outcome of many interrelated chemical processes. Iron-57 tracers may help to follow and unravel those corrosion processes. They could also probe effects of different metal alloy compositions and exposure environments in tests of the longevity of steel infrastructure or of conservation methods for historical artifacts.

For now, our findings from the synthetic iron minerals we’ve “planted” in rice paddy soils are shaping understanding of the chemistry of periodically flooded soils, revealing that just like plants, the life cycles of iron minerals depend on the composition of and conditions in the soil. With continuing research in soils and with new applications focused on other natural and engineered environments, scientists can gain needed insights into how iron in its many forms affects vital issues from soil health and pollution transport to carbon storage and energy production.

Acknowledgments

This research was carried out as part of the European Research Council–funded IRMIDYN (Iron Mineral Dynamics in Soils and Sediments) project at ETH Zurich. The research was led by Ruben Kretzschmar with team members Laurel ThomasArrigo, Katherine Rothwell, Luiza Notini, Katrin Schiedung (published as Katrin Schulz), Joëlle Kubeneck, Andrew Grigg, Pierre Lefebvre, Sara Martinengo, and Giulia Fantappiè, while each was affiliated with the Institute of Biogeochemistry and Pollutant Dynamics at ETH Zurich, in Switzerland. We acknowledge important contributions to the research made by Kurt Barmettler (ETH Zurich) and Worachart Wisawapipat (Kasetsart University).

Author Information

Andrew R. C. Grigg (andrew.grigg@usys.ethz.ch), Institute of Biogeochemistry and Pollutant Dynamics, ETH Zurich, Zurich, Switzerland; Katrin Schiedung, Thünen Institute, Braunschweig, Germany; Joëlle Kubeneck, TNO–Geological Survey of the Netherlands, Utrecht; also at Radboud University, Nijmegen, Netherlands; and Ruben Kretzschmar, Institute of Biogeochemistry and Pollutant Dynamics, ETH Zurich, Zurich, Switzerland

Citation: Grigg, A. R. C., K. Schiedung, J. Kubeneck, and R. Kretzschmar (2025), Tracing iron’s invisible transformations just beneath our feet, Eos, 106, https://doi.org/10.1029/2025EO250347. Published on 19 September 2025. Text © 2025. The authors. CC BY-NC-ND 3.0
Except where otherwise noted, images are subject to copyright. Any reuse without express permission from the copyright owner is prohibited.

Two billion years ago, a massive star exploded. When its light reached Earth in 2021, it joined more than 20,000 recorded supernova candidates observed that year.

This one was unique, however. It exhibited features not shared by any other known stellar explosion: The star had shed almost all of its outer layers before it died, exposing a core rich in silicon and sulfur.

SN 2021yfj, as this supernova is labeled, revealed never before seen details about stellar interiors. Precisely how a star could die this way is a marvelous puzzle that may help researchers learn about the deaths of the most massive stars and how they spread new elements through the cosmos.

“By studying supernovae, we can develop ideas of how stars form, evolve, and die,” said Steve Schulze of Northwestern University in Illinois, who led the observations and analysis of SN 2021yfj, published in Nature.

Onions Have Layers, Stars Have Layers

All stars, including the Sun, spend the majority of their life cycles fusing hydrogen into helium in their cores, which are surrounded by a hydrogen plasma envelope. When this fuel is exhausted, the core contracts and begins fusing helium into carbon and oxygen. For the most massive stars (those at least 8 times the mass of the Sun) this process continues to fuse heavier and heavier elements in the core.

The result is an onion-like (or ogre-like) character of aging high-mass stars: a hydrogen envelope surrounding a shell of helium, around a shell of carbon and oxygen. Layers of neon, magnesium, silicon, sulfur, and higher-mass nuclei form deeper toward the core. Eventually the energy produced by fusion is no longer able to maintain the core’s integrity, at which point the star explodes as a supernova.

This is the story theory tells, at least; these shells aren’t visible to telescopes. Astronomers must deduce the makeup of interiors from the spectrum of light stars emit when they explode.

“The spectra of supernovae are their fingerprints.”

“The spectra of supernovae are their fingerprints,” said Maryam Modjaz, an astronomer at the University of Virginia who was not involved in the study. She called this type of research stellar forensics. “We see the explosion of the star and we work backwards.”

However, very massive stars shed a great deal of their outer envelopes long before they explode, as astronomers observed during the dramatic dimming of Betelgeuse in 2019. Some extremely massive specimens known as Wolf-Rayet (pronounced “rah-YAY”) stars expel their envelopes much earlier in their lifetimes. The most commonly observed type of Wolf-Rayet stars consist of a hydrogen nebula swathing the extremely hot layers surrounding the core, which is dominated by emissions from helium and carbon.

I Like That Spectrum—That Is a Nice Spectrum

SN 2021yfj took this early-shedding process further than any other star yet observed: It had shed not only its hydrogen envelope, but also its helium, carbon, and oxygen shells. The spectrum Schulze and his colleagues measured exhibited emissions from ionized silicon and sulfur, indicating the progenitor had ejected that layer before exploding.

“The progenitor star [of supernova 2021yfj] had essentially lost almost all of its shells,” Schulze said. Astronomers have observed other stars that have been stripped of their outer layers, but never to this extreme.

“We have spectra from hundreds of thousands of supernovae, [and] this is the first time we’ve seen deep into the guts of a dying star.”

Though that provided strong evidence supporting the onion model for high-mass stars, it also was surprising: Nobody expected a star to shed that much material before going supernova.

“We have spectra from hundreds of thousands of supernovae, [and] this is the first time we’ve seen deep into the guts of a dying star,” Modjaz said. “This must be a very unique, very uncommon explosion and therefore [uncommon] progenitor.”

“The properties of supernova 2021yfj are so extreme that it’s challenging to find a model that can describe all of the observations,” Schulze said.

“Our leading hypothesis or leading idea,” he continued, “is that it was a very massive star, around 60 times more mass than the Sun.” Because it had already shed its hydrogen and helium by the time it was observed, though, the star was probably even more massive when it was born. He cautioned against trying to make too many guesses based on the data so far. “Exactly how massive it was will require very detailed simulations [and] the development of models that don’t exist yet.”

Schulze noted that even with hundreds of thousands of identified supernovae, astronomers have yet to see all the possible types. To make things more challenging, supernovae—bright as they are—are single points of light that fade over a matter of days, so spotting them often involves a degree of luck. Extreme stripped-core supernovae are so rare, just by probability astronomers will find tens of thousands more typical explosions before the next example turns up in their data.

However, that task is less daunting than it sounds.

In addition to the Zwicky Transient Facility where astronomers detected SN 2021yfj, Schulze and Modjaz both hailed the Vera C. Rubin Observatory, which is expected to detect a thousand supernovae each night of operation when it comes online in 2026. Though that telescope isn’t being built for spectroscopy, its ability to scan huge swaths of the sky at once will let astronomers identify explosions to analyze in more detail quickly, bringing us closer to an understanding of how massive stars live and die.

—Matthew R. Francis (@BowlerHatScience.org), Science Writer

Citation: Francis, M. R. (2025), This star stripped off its layers long before exploding, Eos, 106, https://doi.org/10.1029/2025EO250340. Published on 19 September 2025. Text © 2025. The authors. CC BY-NC-ND 3.0
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