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Source: Geophysical Research Letters

Ancient Mars boasted abundant water, but the cold and dry conditions of today make liquid water on the Red Planet seem far less probable. However, the Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) detected strong radar reflections from a 20-kilometer-wide area over the base of Mars’s southern polar ice cap, hinting at the possibility of liquid water below the icy surface. Such a finding would have major implications for the planet’s possible habitability.

But sustaining liquid water underneath the ice might not be feasible without very salty brines or localized volcanic heat. Scientists have deliberated about other possible “dry” explanations for the bright reflections detected by MARSIS, such as layers of carbon dioxide and water ices or salty ice and clay causing elevated radar reflectivity.

Aboard the Mars Reconnaissance Orbiter, the Shallow Radar (SHARAD) uses higher frequencies than MARSIS. Until recently, though, SHARAD’s signals couldn’t reach deep enough into Mars to bounce off the base layer of the ice where the potential water lies—meaning its results couldn’t be compared with those from MARSIS.

However, the Mars Reconnaissance Orbiter team recently tested a new maneuver that rolls the spacecraft on its flight axis by 120°—whereas it previously could roll only up to 28°. The new maneuver, termed a “very large roll,” or VLR, can increase SHARAD’s signal strength and penetration depth, allowing researchers to examine the base of the ice in the enigmatic high-reflectivity zone.

Morgan et al. examined 91 SHARAD observations that crossed the high-reflectivity zone. Only when using the VLR maneuver was a SHARAD basal echo detected at the site. In contrast to the MARSIS detection, the SHARAD detection was very weak, meaning it is unlikely that liquid water is present in the high-reflectivity zone. The researchers suggest that the faint detection returned by SHARAD under this portion of the ice cap is likely due to a localized region of smooth ground beneath the ice. They add that further research is needed to reconcile the differences between the MARSIS and SHARAD findings. (Geophysical Research Letters, https://doi.org/10.1029/2025GL118537, 2025)

—Rebecca Owen (@beccapox.bsky.social), Science Writer

Citation: Owen, R. (2025), Maybe that’s not liquid water on Mars after all, Eos, 106, https://doi.org/10.1029/2025EO250437. Published on 21 November 2025. Text © 2025. AGU. 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.

Editors’ Highlights are summaries of recent papers by AGU’s journal editors. Source: Journal of Geophysical Research: Solid Earth

Continental extension often unfolds in multiple deformation phases, where earlier faults steer the geometry and behavior of later ones. In a new study, Liu et al. [2025] explore the complexity of fault interaction by analogue modeling. 

The models reveal how shifts in stress—from biaxial to triaxial and back—govern the evolution of the fault network. In the triaxial phase, faults from the earlier biaxial phase are reactivated and new conjugate faults appear. When stress shifts back to biaxial, older faults may become inactive or partly reactivated. Stress conditions determine whether old faults block or guide the growth of new ones. Their modeling results are applied to explain the patterns of abandoned, reactivated and newly developed faults seen in the Aegean and Barents Seas. In general, their findings help to shed light on both the tectonic history of their study areas and the distribution of earthquakes.

Citaiton: Liu, J., Rosenau, M., Kosari, E., Brune, S., Zwaan, F., & Oncken, O. (2025). The evolution of fault networks during multiphase triaxial and biaxial strain: An analogue modeling approach. Journal of Geophysical Research: Solid Earth, 130, e2025JB031180. https://doi.org/10.1029/2025JB031180

—Birgit Müller, Associate Editor, JGR: Solid Earth

Text © 2025. The authors. CC BY-NC-ND 3.0
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The explosiveness of a volcanic eruption depends on how many gas bubbles form in the magma—and when. Until now, it was thought that gas bubbles were formed primarily when the ambient pressure dropped while the magma was rising.

Across Europe, scientists and citizens are uncovering a hidden legacy of contamination beneath their feet. From Denmark's first PFAS crisis to a new generation of soil-mapping initiatives, a continent is learning to see—and stop—the pollution it once ignored

Imagine trying to predict wind patterns as air flows across a landscape. It's a straightforward task over a flat plain—but becomes more complex when the terrain shifts to jagged mountain ranges. Here, wind does not simply sweep over peaks; it is deflected, slowed, and forced into gravity waves.

A recent study led by scientists at NASA's Jet Propulsion Laboratory in Southern California and the nonprofit Aerospace Corporation shows how high-resolution maps of ground-level ammonia plumes can be generated with airborne sensors, highlighting a way to better track the gas.

A mysterious swarm of earthquakes that occurred near the Greek island of Santorini in early 2025 was caused by rebounding sheets of magma slicing through Earth's crust, according to a new study by an international team involving a UCL (University College London) researcher.

While it is well known that climate change is heating the world's oceans, it was thought that the deep sea was safe from its effects—until now. Researchers have discovered that a rapidly warming part of the Atlantic is leading to the heating up of Arctic Ocean depths.

body {background-color: #D2D1D5;} Research & Developments is a blog for brief updates that provide context for the flurry of news that impacts science and scientists today.

Rising sea levels have put thousands of facilities containing hazardous materials at risk of flooding this century, according to a new study published in Nature Communications. 

Global sea level rise is accelerating, leading to an increase in coastal flooding that scientists expect to worsen. As seas rise, floodwater reaches infrastructure that was not built to withstand it.

“Flooding from sea level rise is dangerous on its own—but when facilities with hazardous materials are in the path of those floodwaters, the danger multiplies.”

These extreme events can release toxins into the environment. For example, an estimated 10 million pounds of pollutants from refineries, petrochemical facilities, and manufacturing sites spilled into the environment following flooding from Hurricane Harvey in 2017.

The new study reports that 5,500 facilities containing hazardous substances are at risk of a similar event, threatening the health of nearby communities. 

“Flooding from sea level rise is dangerous on its own—but when facilities with hazardous materials are in the path of those floodwaters, the danger multiplies,” Lara Cushing, an environmental researcher at the University of California, Los Angeles and lead author of the new study, told The Guardian. 

In the study, scientists analyzed the location of 47,646 coastal power plants, sewage treatment facilities, fossil fuel infrastructure sites, industrial facilities, and former defense sites. Then, they used sea level rise projections under various climate scenarios to determine whether those sites were at risk from a 1-in-100-year flood event by 2100. 

They found that 11% of the sites analyzed were at risk of such a flood by 2100 in a high-emissions, business-as-usual scenario (RCP 8.5). Eighty percent of the at-risk sites were in just seven states: Louisiana, Florida, New Jersey, Texas, California, New York, and Massachusetts. Oil and gas wells made up a large proportion of sites considered to be at risk. 

These maps and graphs show the number and types of coastal facilities at risk of flooding due to sea level rise by 2050 and 2100 under a high-emissions, business-as-usual scenario. Credit: Cushing et al. 2025, doi:10.1038/s41467-025-65168-2, CC BY 4.0

In total, 22% of coastal sewage treatments facilities, 24% of coastal refineries, 44% of coastal fossil fuel ports and terminals, 12% of coastal industrial facilities, 21% of former coastal defense sites, and 21% of coastal fossil fuel and nuclear power plants are at risk of flooding by 2100. 

Disproportionate Effects

Marginalized groups are more likely to live near hazardous waste sites and industrial facilities, making these groups more vulnerable when such facilities flood. 

In the study, researchers analyzed the location of at-risk sites compared to community demographics. They found that households in Hispanic neighborhoods, households with incomes below twice the federal poverty line, and households that rented rather than owned their homes were especially likely to be located within one kilometer (0.62 miles) from a facility at risk of flooding.

 
Related

•  Read the study: “Sea level rise and flooding of hazardous sites in marginalized communities across the United States.”
•  Climate Central Report: Toxic Tides
•  Thousands of Toxic Sites Across U.S. Face Risk of Coastal Flooding
•  Sea Level Rise Threatens Hundreds of Wastewater Treatment Plants
• Sea Level Rise May Swamp Many Coastal U.S. Sewage Plants
 

“These projected dangers are falling disproportionately on poorer communities and communities that have faced discrimination and therefore often lack the resources to prepare for, retreat, or recover from exposure to toxic floodwaters,” Cushing said.

Reducing greenhouse gas emissions is key to slowing sea level rise and reducing flooding. The study’s projections showed that restricting greenhouse gas emissions to a low-emissions scenario (RCP 4.5) would reduce the number of at-risk sites from 5,500 to 5,138. 

In addition, the authors write that keeping communities safe from future hazardous floodwaters will require federal and state governments to “provide publicly available, accessible, and continually updated data on projections of [sea level rise]-related flooding threats.”

—Grace van Deelen (@gvd.bsky.social), Staff Writer

These updates are made possible through information from the scientific community. Do you have a story about science or scientists? Send us a tip at eos@agu.org. Text © 2025. AGU. CC BY-NC-ND 3.0
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Climate change will make monsoon storms in South Asia wetter and weaker, with more storms pushing further inland across India.

As global efforts intensify around restoring coastal wetlands to curb climate change, a new JCU-led study published in Reviews of Geophysics is the first to link wetland restoration and carbon cycling with groundwater dynamics, showing that subsurface flows can tip the balance from storing carbon to emitting it.

After a long and deadlocked bidding process for Australia and Pacific Island nations to co-host the UN climate summit (COP31), the event will now be hosted by Turkey. Australia's Climate Minister, Chris Bowen, will reportedly take a key role as "COP President for negotiations". More details are yet to emerge.

In recent years, more and more lobbyists from the oil, gas and coal industries have taken part in international climate negotiations. Estimates of lobbyist numbers have risen sharply, from 503 at the 2021 Glasgow talks to 1,773 at last year's talks in Azerbaijan's capital Baku.

Over the past week we've witnessed the many political discussions that go with the territory of a COP—or, more verbosely, the Conference of the Parties to the United Nations Framework Convention on Climate Change.

Magnetic data collected in the late 1960s has been brought back to life by a research team including a Keele scientist, who have used it to learn more about how the continent of Africa is stretching and splitting apart.

The world is warming, yet summer temperatures on the southern slope of Mount Everest, measured continuously by the Pyramid Laboratory since 1994, have dropped over the past 15 years.

The reason? Cold downslope winds, caused by the increased temperature differences between the warmer air above the glacier and the air mass in direct contact with the glacier’s frozen surface.

These katabatic winds create a cooling effect around mountain glaciers, explained Thomas Shaw, a glaciologist at the Institute of Science and Technology Austria. “They’re melting more slowly than they would if there was a one-to-one correspondence between atmospheric temperature and the temperature of the glacier boundary layer.”

Scientists have made note of this phenomenon since the late 1990s, but studies have so far been limited to specific glaciers.

To understand the phenomenon’s extent and the factors influencing it on a global scale, Shaw and his colleagues collected and analyzed a dataset from 62 glaciers across 169 glacier campaigns, amounting to an unprecedented 3.7 million hours of air temperature data.

While much of the data were easily accessible, some were “almost the equivalent of being written on the back of a napkin,” said Shaw, who was able to include previously unpublished data from other researchers. “It takes a lot of emailing, clicking, finding, searching, and thinking, ‘Oh, I remember there was someone that published something on this.’”

Changing Projections

The study, published in Nature Climate Change, found that the glacier boundary layer warms an average of 0.83°C for every degree of ambient warming.

“This is not the only process affecting glacier melt, but it’s an important one that we didn’t have proof of before,” said Inés Dussaillant, a glaciologist at Centro de Investigación en Ecosistemas de la Patagonia in Chile who was not involved in the study.

“It may change our projections…and IPCC reports for the future evolution of glaciers or sea level contribution.”

Currently, this effect is not taken into account when modeling how glaciers will change over time, said Harry Zekollari, a glaciologist at Vrije Universiteit Brussel in Belgium who was not involved with the study. “It may change our projections and how we make them, and it may change projections and [Intergovernmental Panel on Climate Change] reports for the future evolution of glaciers or sea level contribution.”

According to Shaw’s analysis, the main factors driving the cooling effect are the temperature difference between the glacier boundary layer and the surrounding air, the size of the glacier, and humidity. Debris cover on the glacier and strong synoptic winds hinder the effect.

This phenomenon means that rising ambient temperatures actually increase the cooling effect on large glaciers—but only up to a point. “Glaciers are not protected because of this; they’re not cooling. It’s a bit of a misnomer,” said Shaw. While they are melting more slowly than would be expected with linear warming, the effect is still substantial. The study projects that globally, these near-surface cooling effects will peak during the late 2030s as temperatures rise.

As glaciers shrink in size, they will no longer be able to generate katabatic winds, and their rate of warming will begin to reflect ambient temperatures. According to the study, this will lead to accelerated melting from mid-century onward.

Going, Going, Gone

Shaw and his coauthors noted large regional variations in the data. While the cooling effect is not expected to peak until the 2090s for glaciers in New Zealand and the southern Andes, glaciers in central Europe have likely already passed this mark and are deteriorating at an increasing pace.

The study’s results tally with other findings. Earlier this year, a study of global glacier mass changes found that central Europe lost 39% of its ice mass between 2000 and 2023, faring the worst of all 19 regions studied.

A prime example is Pasterze, an Austrian glacier where research into the cooling phenomenon first started in the 1990s. “This was once a much larger glacier, with a much stronger observed katabatic cooling effect. Now it’s disintegrating very fast,” said Shaw, noting it will likely not be Austria’s largest glacier for much longer. “It’s already showing evidence of how rapidly glaciers can react to climate when they begin to disappear.”

But while troves of reliable long-term data are available for areas like the European Alps, Iceland, Svalbard, and western North America, glacier monitoring is not equally distributed worldwide. Dussaillant would like to see more support for regions where governments are not able to maintain ongoing glacier monitoring. “We cannot really say that this is the global picture, when in fact, some regions still have huge gaps which we need to fill and better understand.”

With around 200,000 glaciers worldwide, there is, indeed, still a lot of work to be done before a truly global picture emerges, said Zekollari. “But it’s a massive step forward compared to what we had.”

—Kaja Šeruga, Science Writer

Citation: Šeruga, K. (2025), Glaciers are warming more slowly than expected, but not for long, Eos, 106, https://doi.org/10.1029/2025EO250430. Published on 20 November 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.

Thin layers of sedimentary rock in Mars’s Gale Crater suggest that the planet once had a moon much larger than the two that orbit it today, according to work to be presented at AGU’s Annual Meeting 2025 on 17 December. Unlike the current Martian moons Phobos and Deimos, the gravitational pull of the hypothesized moon would have been strong enough to create tides in bodies of water on or below the planet’s surface.

The team analyzed images from cameras on the Curiosity rover, which has been trundling across Gale Crater since 2012. The Mars Hand Lens Imager, for instance, captures images with resolutions up to 13.9 micrometers per pixel.

Pictures of a rocky outcrop snapped during four Martian days in late 2017 and early 2018 revealed a section of fine, repeating layers in alternating light and dark colors. The researchers interpret those layers as tidal rhythmites, or sediments deposited by the regular back-and-forth sloshing of the tides.

“Our study provides sedimentary evidence for the case of tidally deposited rhythmites, hinting at a past larger moon for Mars.”

“Our study provides sedimentary evidence for the case of tidally deposited rhythmites, hinting at a past larger moon for Mars,” Ranjan Sarkar, a planetary scientist at the Max Planck Institute for Solar System Research in Gottingen, Germany, told Eos via email. “This, in turn, aligns with the hypothesis that Mars has repeatedly had larger moons that were tidally destroyed into rings, which then reformed into successively smaller moons.” That is, the larger moon or moons would have been pulled apart by the force of Martian gravity, which would have exerted a stronger pull on the planet-facing side of the moon than the opposite side.

The layering was detected at Vera Rubin Ridge on the flank of Mount Sharp, a sedimentary peak in the middle of Gale Crater. The studied area was about 35 centimeters long and 20 centimeters thick. Individual bands in the rock ranged from submillimeters to millimeters thick, with wider, light-toned bands and darker, thinner bands.

This graphic, for presentation at AGU’s Annual Meeting 2025, traces Curiosity’s path to the Jura outcrop on Vera Rubin Ridge. Color-enhanced images from the rover show the layered rocks interpreted as evidence of tidal rhythmites, with similar layers in an Earth setting shown for comparison. Click image for larger version. Credit: Ranjan Sarkar, Priyabrata Das, Suniti Karunatillake

Comparison with other observations along the ridge suggests the layers were deposited roughly 3.8 billion years ago, when Gale Crater contained a lake.

“Back-of-the-Envelope” Profile

Not all rhythmites are tidal: Similar sedimentary layers can be deposited by winds, seasonal variations in precipitation or glacier melts, or other processes, the researchers note.

“The finely laminated rhythmites in this crater are most likely varves, or deposits that reflect seasonal changes in the climate,” said Bob Craddock, a geologist at the National Air and Space Museum who was not involved in the study. More water flows into a lake during the warmer summer months, producing thicker sediment layers with larger grains compared to those laid during winter, he said. “As this continues through time, you get rhythmites.”

“It’s very tricky. We can’t be decisive, so our argument is one of consistency.”

Sarkar, however, said the structure of these layers doesn’t match what would be expected of seasonal deposits. “Annual varves usually show simple light-dark couplets, but we observe alternating thick-thin bands showing paired dark laminae,” he said. Such patterns “are commonly used as markers of tidal sedimentary signatures on Earth.”

“It’s very tricky,” said team member Suniti Karunatillake, a geologist and geophysicist at Louisiana State University. “We can’t be decisive, so our argument is one of consistency.…We felt that the observations are generally more consistent with a tidal setting.”

The layers probably were deposited with a “monthly” cycle of about 30 days, Karunatillake said. Even if Phobos or Deimos were much closer to Mars than they are today, neither is massive enough to create such a tidal cycle. Instead, combining this new work with modeling by previous researchers, the team estimated the tides were raised by a body at least 18 times the mass of Phobos, the larger moon, orbiting at an altitude of about 3 times the radius of Mars.

Phobos, photographed by the Mars Reconnaissance Orbiter, is not massive enough to have raised tides on Mars. It could be a remnant of a larger moon that was destroyed in a giant impact. Credit: NASA/JPL-Caltech/University of Arizona

“That’s our back-of-the-envelope calculation,” Karunatillake said. “Anything smaller and it would be difficult to induce this type of tidal activity, especially when you consider that Gale Crater is quite small as a water body on the planetary scale.”

The possibility of a smaller moon causing the observed tidal activity might be more realistic, Karunatillake added, if there were a connection between Gale Crater and the northern ocean, but no connection has yet been seen. However, even a subterranean link, such as the network of flooded caves and tunnels beneath Earth’s Yucatán Peninsula that leads to the Caribbean Sea, would suffice. “There are instances where you get tidal variations inland, as long as there’s a subsurface connection with the ocean,” he said.

Pondering the Martian Moons

Planetary scientists have pondered the origins of Phobos and Deimos extensively in recent decades. The original theory said they were captured asteroids, but it’s not easy for a planet to nab even one asteroid, much less two.

Some studies have suggested that Mars originally had a larger moon—either a captured asteroid or one that formed from an early giant impact. That body then could have been pulverized by the gravity of Mars or by its own collision, forming a ring that then gave birth to smaller moons. In fact, such a scenario could have played out multiple times. “Our study provides actual (ground) evidence, from measured laminae periodicities, for the predicted/hypothesized past larger moon,” Sarkar said.

The researchers are considering conducting a detailed celestial mechanics study to refine their estimates of the mass, distance, and orbital period of the proposed moon. They’re also examining two other sites in Gale Crater that appear to show similar tidal rhythms.

Any inconsistencies among the sites would “dispute our model, and possibly falsify it,” Karunatillake said. “But any agreement would take us toward a stronger argument for an ancient large moon.”

—Damond Benningfield, Science Writer

Citation: Benningfield, D. (2025), Sediments hint at large ancient Martian moon, Eos, 106, https://doi.org/10.1029/2025EO250434. Published on 20 November 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.

Editors’ Highlights are summaries of recent papers by AGU’s journal editors. Source: Geophysical Research Letters

How do the deep forces of the Earth’s interior shape surface faults, fractures and rivers? The results of a new global analysis show that rivers, faults, and stresses often align, but the degree of correspondence depends on fault type, stress source, and river size.

Kuhasubpasin et al. [2025] present a new framework to quantify the relative roles of lithospheric structures and mantle dynamics, offering fresh insights into how deep Earth processes govern the surface. A novel procedure is proposed to assess the relative role of mantle flow and lithospheric differences to the surface features, which may help constrain the individual forces acting to deform the lithosphere, creating topography. This holistic perspective on the coupled evolution of Earth’s interior and its surface shows how the interior of the Earth affects and perhaps even controls the surface.

Citation: Kuhasubpasin, B., Moon, S., & Lithgow-Bertelloni, C. (2025). Unraveling the connection between subsurface stress and geomorphic features. Geophysical Research Letters, 52, e2025GL116798. https://doi.org/10.1029/2025GL116798

—Fabio A. Capitanio, Editor, Geophysical Research Letters

Text © 2025. The authors. CC BY-NC-ND 3.0
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The tectonic plates under Africa and Asia are slowly drifting apart, as the Gulf of Suez that separates these two land masses continues to widen at a rate of about 0.26–0.55 millimeters per year.

If heat-trapping pollution from burning coal, oil and gas continues unchecked, thousands of hazardous sites across the United States risk being flooded from sea level rise by the turn of the century, posing serious health risks to nearby communities, according to a new study.