Marmolada glacier is shrinking

 Researchers warn that Italy’s Marmolada Glacier may disappear by 2040 as a result of global warming

The 3,343-meter Marmolada, known as the “Queen of the Dolomites,” is losing between 7 and 10 cm's of ice every day. In the past five years, it lost the equivalent of 98 football pitches. The Marmolada glacier, the highest glacier of the Dolomites and an UNESCO World Heritage site, is disappearing and could melt away completely by as early as 2040. The Marmolada Glacier in Italy's Dolomite mountains has dropped in surface area from 92 hectares down to 83 hectares, losing nine hectares in a single year due to intense summer heat waves. The 3,343-meter glacier, located in the Alps mountain range in northeastern Italy and also known as the “Queen of the Dolomites,” is disappearing at a rate of between 7 and 10 cm's a day, a recent assessment has revealed. It lost around 50% of its original surface in the past century and another 50% in the past decade. Since 2019, the glacier shrank by an additional 70 hectares or the equivalent of 98 football pitches. Recent data shared by researchers from the University of Padua, the Veneto environmental protection agency (ARPAV), and the Italian Glaciological Foundation highlights an alarming acceleration in the melting of the highest glacier in the Dolomites. The area covered by ice has fallen from 92 hectares to 83 over the past 12 months. It stood at 100 in 2023. Some of the important factors are as follows:-

The ice retreated by an average of about 23 meters this summer alone.

Dropped by 9 hectares in one year, shrinking the total area from 92 to 83 hectares.

The glacier loses between 7 and 10 cm's of ice depth daily during peak summer conditions.

Researchers warn that if current extreme summer melting patterns continue, the entire glacier could disappear in roughly next one decade. 

The trend is negative. This is because the Marmolada glacier is retreating and shrinking. Compared with last year, its area has decreased by 9 hectares and is ‘a long way’ from the 100 hectares recorded in 2023. on the western flank, a retreat of 120 metres has been recorded over two years. This is what has emerged from the eighth edition of the participatory glaciological campaign on the Marmolada, promoted by the Museum of Geography at the University of Padua, which involved collaboration between researchers from the University of Padua, ARPAV, the Italian Glaciological Foundation, students and volunteer members of the public from four different regions. ‘The 2026 campaign,’ the organisers emphasise, ‘has enabled us to collect up-to-date data, which is essential for continuing to monitor what remains of the Dolomites’ main glacier and for better understanding the impact of climate change at a local level.’ In 2020, the environmental group and the international commission for the protection of the Alps (Cipra) launched the campaign Caravana dei Ghiacciai (Caravan of Glaciers) in partnership of the Italian Glacier Committee. Speaking with reporters after their latest expedition, the team of scientists behind the campaign said the Marmolada is a “suffering glacier” in an “irreversible coma.” The melting ice, they explained, is leaving a desert of white flat rock behind.

The data collected this year, as Mauro Varotto, a lecturer in the Department of Historical, Geography and Classical Studies and the campaign’s scientific lead, “exacerbate the trend already evident in recent decades, setting a new record low for the glacier’s area loss: in one year, it has lost 9 hectares, falling to a total of 83 hectares compared with 92 last year”. ‘This is a record loss that we had previously recorded only in 2022,’ he emphasises, citing the results of the analysis of satellite imagery carried out by Francesco Ferrarese, ‘following the tragic collapse of the glacier. If summers like the one just passed continue, the glacier could have only about ten years left.” Around thirty people, aged between 16 and 75, took part in the monitoring activities carried out on the glacier, including experienced hikers, teachers, as well as ordinary enthusiasts and curious onlookers. ‘Overall, measurements at the glacier’s front show a retreat three times greater than last year, 23 metres on average,’ emphasises Giovanni Benetton, who has been in charge of measurements for the Italian Glaciological Foundation since this year, and the most dramatic situation is at the western front, where at one measuring point we recorded a retreat of 120 metres in two years, with the front now at an altitude of over 2,900 metres. The glacier is completely devoid of residual snow, and the only snow remaining is now that beneath the geotextile tarpaulins.

“[W]e have recounted the suffering of a dying glacier, marked by an acceleration of the melting process that has impressive numbers and that requires urgent responses starting from sustainable governance of the territory,” said Vanda Bonardo, national Alpine Coordinator for Legambiente and President of Cipra. But this, she explained, is just the latest example of how the climate crisis is impacting the Alps, one of Europe’s highest and most extensive mountain ranges. “The Alps are a fundamental place at a national and European level, but they are also increasingly fragile due to the advancing climate crisis,” said Bonardo. The Intergovernmental Panel on Climate Change (IPCC) predicts that temperatures in the Alps will rise by 1-3C by 2050. “The summer of 2026 turned out to be the hottest at high altitude in the Dolomites since at least 1991, surpassing even that of 2003 in terms of duration and average temperatures,” comments Gianni Marigo of Arpav. Taking August as an example, the deviation from the average was more than 3 degrees Celsius. During that month, at the Arpav Punta Rocca station on the Marmolada at 3,250 metres, a sub-zero minimum (-0.6°C absolute value) was observed on only three days, and no day was recorded with a sub-zero average temperature.” Not only that: ‘The intense glacier ablation processes have thus continued,’ he continues, ‘and there were no snowfalls even at the highest altitudes; similarly, the degradation of the permafrost has continued, and at the Piz Boè station there is no frozen ground at any depth.’ Alberto Lanzavecchia of the University of Padua highlighted the educational aspect of the campaign and, at the same time, the importance of the glaciers. 

And thus the importance of monitoring the site, one of the 150 that the Italian Glaciological Foundation ‘monitors’ each year. “‘2026 is proving to be a record year even on an Alpine scale, with losses in glacier thickness in this region tripling compared to the average of the last decade and winter snow having already melted away by the end of July, weeks earlier than usual,’ concludes Aldino Bondesansi, the regional manager for the Triveneto area. In mid-August, in Marmolada, surveys showed that the crevasses upstream of the 2022 detachment niche were filled with melt water, the very same condition that our studies had identified as the cause of the collapse.” Severe summer temperatures in the Alps caused winter snowpacks to melt completely weeks ahead of schedule by the end of July. Freezing levels frequently surpassed 4,000 meters, leaving even high-altitude stations without negative average temperatures for weeks. Meltwater pooling inside glacial crevasses continues to weaken the internal structure of the remaining ice, raising concerns similar to those that preceded the tragic 2022 collapse.

Scientists have repeatedly warned that the largest glaciers in the Alps, namely the Adamello and Forni, are experiencing similar challenges. The Forni Glacier is losing ice at a rate comparable to that of the Marmolada. Meanwhile, long-term measurements of the 3,539-meter Adamello indicate that its current surface is primarily composed of snowfall from the 1980s, highlighting the significant and ongoing decline in glacial mass. Since the end of the 19th century, the Adamello glacier has retreated by approximately 2.7 km's. 68% of the world’s glaciers are set to disappear at the current global warming rate, with at least half of the loss taking place in the next 30 years, a 2023 study revealed. By 2100, central Europe, western Canada and the US will have no glaciers left. Even under the most optimistic scenario of 1.5C of global warming set out in the Paris Agreement, 49% of the planet’s glaciers, not including the Greenland and Antarctic ice sheets, would still melt completely, the study said.

Around 10% of the world’s land surface is currently covered by glaciers, which store 70% of the Earth’s freshwater. Melting glaciers contribute significantly to sea level rise. Between 2000 and 2019, meltwater from glacier and ice sheet loss alone accounted for 21% of the global sea level rise. Glacial melting also threaten water supplies for up to 2 billion people and increase the risk of natural hazards and extreme weather events such as flooding. With global warming and rising temperatures, these massive ice bodies are retreating at unprecedented rates. Between 1994 and 2017, glaciers worldwide lost nearly 30 trillion tons of ice and they are now melting at a rate equivalent to 1.2 trillion tons a year. Among the glaciers that are disappearing the fastest are those located in the Alps, Iceland and Alaska. 

New Form of Ice at more than 2,000 °C

A new form of Ice created at more than 2,000 °C by Scientists 

Water is one of the most commonplace, essential substances in the human world. Ice comes in more forms than what you’ll find in a freezer or a glacier. Since 1900, scientists have observed more than 20 phases of ice, many of them shaped under extreme conditions. The growing list includes hot ice and even ice that conducts electricity. But if just considered as a liquid, water is extremely weird, behaving in ways completely at odds with other liquids. It becomes less dense when it freezes. Its surface tension is bizarrely high. So is its boiling point. And, based on its molecular weight, it should be a gas at room temperature. We literally can't function without its properties as a near-universal solvent. It falls from the sky. We bathe in it, drink it, and immerse ourselves in it for fun. And that's all at normal, ambient Earth conditions. Tweak the pressure and the temperature a few notches, and water's outlandish behavior gets even more out of hand.

Scientists have now demonstrated one of the weirdest forms of ice yet, under preposterous pressures up to 2.3 million atmospheres, and tremendous temperatures up to 2,630 kelvins (2,357 degrees Celsius, or 4,274 degrees Fahrenheit). At those temperatures, you'd normally expect water to emphatically be a gas, even partially sundered into its constituent oxygen and hydrogen atoms. But something interesting happens at the astronomical pressures found deep inside planets. When water transitions from a liquid to a gas, or vapor, it expands. Under crushing pressures of millions of atmospheres, this expansion is stymied. Instead, water can remain extraordinarily dense, taking on exotic forms unlike any ice we encounter at Earth's surface. One of these is superionic ice, a deeply odd state of matter that's neither entirely solid nor entirely liquid. Its oxygen atoms remain fixed in a rigid crystal lattice, as they would in a solid. But the hydrogen nuclei are mobile, diffusing through that lattice more like particles in a liquid.

At slightly different sets of conditions, the arrangement of the oxygen atoms shifts into different configurations known as phases. There are some twenty-something known phases of water ice, a few of which become superionic under extreme conditions. Scientists are always looking for more. And it's not just weirdness for weirdness's sake. Superionic ice is thought to exist deep inside Uranus and Neptune, where its unusual properties may play a role in generating the planets' equally unusual magnetic fields. Ice is the name for any phase of water that is solid and crystalline, meaning that it has a repeating molecular structure. Over the past decade, computer simulations have predicted tens of thousands of possible forms of ice. Though uncommon on our planet, exotic ice may exist in off-Earth environments, from cold and amorphous comet tails to the hot and crushing cores of icy planets. Ice comes in many more forms than the cubes in your water glass. Scientists have found many phases of ice, and according to simulations, there could be many more out there.

In a new experiments, a team led by physicist Alexis Forestier of the French Alternative Energies and Atomic Energy Commission subjected tiny samples of water to the sorts of extreme conditions expected in the interiors of ice giant planets. They squeezed the samples between the tips of diamonds to pressures as high as 230 gigapascals, while using lasers to heat them to thousands of degrees. That's 2.3 million times Earth's atmospheric pressure at sea level, the pressure at the center of Earth, for context, is around 360 gigapascals. Then, using an extremely narrow beam of synchrotron X-rays, they probed for changes in the crystal structure of the ice. What emerged was a configuration predicted theoretically but never unambiguously observed in experiments: hexagonal close-packed, or hcp, ice. As the hcp crystal was heated, its expansion also showed a signature of superionic behavior, suggesting it entered the superionic state at around 1,700 kelvins. The name refers to the arrangement of the oxygen atoms. Imagine you're packing identical balls in layers; there are a number of different ways those layers can be stacked while packing the balls as tightly as possible.

One previously identified form of superionic ice has a face-centered cubic, or fcc, structure. In the newly identified hcp ice, the layers are stacked in a different sequence. The researchers found evidence that one can transform into the other as the layers shift position. This transformation seems to occur as conditions grow more extreme. The conditions under which the researchers observed the new hcp ice phase (filled triangles and filled circles) show its emergence at extreme pressures and temperatures. At 155 gigapascals and 2,000 kelvins, the signal observed from the X-ray probe was a mix of fcc and hcp. Dialing up to 197 gigapascals and 2,250 kelvins, the hcp signature became stronger relative to fcc. By the final set of conditions, 219 gigapascals and 2,630 kelvins, the fcc signature had almost vanished, and hcp clearly dominated. Intriguingly, this may not have been the first time the researchers had produced hcp ice. Looking back at data from an earlier experiment, they realized that a previously unidentified X-ray diffraction peak observed above 130 gigapascals was likely the signature of hcp ice – they just hadn't recognized it at the time. The results suggest that, at pressures above around 200 gigapascals, hcp may become the more stable arrangement of superionic ice.

It seems like a relatively small change, literally on the atomic scale, but the difference could mean big things for the Solar System. If hcp ice conducts electricity differently from fcc ice, its presence deep inside Uranus and Neptune could change models of how material and electrical charge move through their interiors, processes thought to be involved in generating the planets' strange, messy, lopsided magnetic fields. We don't actually know about the properties of hcp ice yet, though. The stuff has only just been discovered. Water is really weird, and superionic ice is even weirder. Scientists have only just scratched the surface of what this strange molecule can do; in a way, it feels fitting that we need to rely on it to stay alive. The findings have been published in Physical Review Letters.

This research explores how water behaves under the extreme conditions found deep inside ice giant planets like Uranus and Neptune. Researchers used laser-heated diamond anvil cells to squeeze water samples under immense pressures surpassing 200 gigapascals (GPa) alongside temperatures over 2,000 °C. Under these crushing pressures, the oxygen atoms in the water molecule rearrange into a hexagonal close-packed (hcp) lattice rather than the face-centered cubic (fcc) arrangement seen in other high-pressure phases. At these blistering temperatures, the material enters a superionic state. This means the oxygen atoms stay locked in their solid crystal grid, while hydrogen nuclei (protons) melt and flow freely through the lattice like a liquid. The researchers invite further theoretical work to tease apart those properties, especially its mechanical plasticity and electrical conductivity. 

Ice giants like Uranus and Neptune harbor extreme interior environments. Knowing that hcp superionic ice can exist stably at these high temperatures alters models of how heat and electrical charges move inside these planets. The unique flow of protons inside this hot, pressurized ice may help explain the strange, lopsided and multi-poled magnetic fields observed around Uranus and Neptune. Scientists note that more experiments and theoretical simulations are required to fully map out the mechanical plasticity and electrical conductivity of this high-temperature hcp phase. Further experiments will also be needed to pin down exactly where, across the extremes of pressure and temperature, hcp ice is stable relative to its fcc counterpart. As physicists put water to the test with improved experimental techniques and keep finding surprises.

Australia's 10-year Antarctic monitoring strategy

 The important role ships, ice cores and krill surveys play in gathering scientific data in Antarctica

This article have highlighted the important role ships play in gathering scientific data in Antarctica and the Southern Ocean has been outlined at a leading Antarctic science conference in Hobart. The biennial Australian Antarctic Research Conference was held at the University of Tasmania and attracted 400 researchers from around the globe. The Australian Antarctic Science Decadal Strategy (the Science Strategy) was released by the Australian Government in February 2025. The Science Strategy supports Australia’s Antarctic national interests, including to conduct world-class scientific research consistent with national priorities. It delivers on the commitment in the overarching Australian Antarctic Strategy and 20-Year Action Plan (the Strategy and Action Plan) to develop a ten-year Antarctic Science Plan to implement Australia’s Antarctic science priorities. Mission is to conduct impactful science in Antarctica and the Southern Ocean which supports Australia’s national interests. And vision is global leadership and excellence in Antarctic and Southern Ocean science which is priority driven, influential and is at the core of Australia’s Antarctic activities. This Science Implementation Plan (the Science Plan) presents the first iteration of science activities to deliver the Science Strategy. It is designed which will evolve to maximise the delivery of science priorities within available resources, and to respond to evolving opportunities and challenges. It will also be agile to align with strategic direction set out in the current Strategy and Action Plan, and any future iterations. 

Dr. Patricia Miloslavich, who leads the Australian Antarctic Division's Antarctic Monitoring Program, said that between 1990 and 2026, the Australian Antarctic Program's Aurora Australis and RSV Nuyina, the French Program's l'Astrolabe and the CSIRO's RV Investigator made 379 voyages, traveled nearly 2.5 million km's (1.6 million miles) and collected 137 million measurements. Sea surface and air temperature data collected by the Aurora Australis alone from 1991 to 2020 showed a close correlation with global climate data from the UN's World Meteorological Organization and increasing "warm" anomalies over that time. "With the Aurora's data alone, we can tell the story we all know by now, which is that both the ocean and the air are getting warmer," Miloslavich said. "For the specific Southern Ocean section covered by the Aurora Australis over 30 years, we can see that air temperatures have increased both north and south of 50°S, which is approximately the boundary between Antarctic climates to the south and mid-latitude climates to the north. "In contrast, sea surface temperatures over that time only increased significantly to the north of 50°S, reflecting the initial delay in human-caused climate change signals appearing in the ocean around Antarctica."

The Australian Antarctic Program (AAP) delivers world class science that advances our Antarctic national interests and supports Australia’s other national interests in Antarctica and the Southern Ocean. AAP science activities are delivered across a range of Australian government agencies, organisations and academic institutions. The Australian Antarctic Division of the Commonwealth Department of Climate Change, Energy, the Environment and Water (DCCEEW) coordinates delivery of AAP science activities in partnership with AAP science partners. Collaborations with other national Antarctic programs and international research institutions further augment Australia’s Antarctic science activities. Together, science partners in the AAP bring the breadth of expertise and research infrastructure needed to address the complex challenges facing Antarctica and the Southern Ocean and achieve the outcomes identified in the Science Strategy. Another long-term, ship-based data collection method, the Continuous Plankton Recorder (CPR), is towed behind ships and samples plankton on a silk ribbon. The CPR Survey is the world's oldest and most geographically extensive marine biological monitoring program. It was initiated in 1931 and implemented in the Southern Ocean by the AAD in 1991. "With the CPR data, we can see that in the Southern Ocean, there's been a shift toward smaller zooplankton, that some species are moving farther south and that there's been a decline in pteropods in some locations," Miloslavich said. Improvements in ship design are contributing to better data collection. Where the Aurora Australis used nets to bring marine creatures on board, destroying many delicate specimens in the process, RSV Nuyina uses a wet well. On the Denman Marine Voyage in 2025, the wet well ingested an intriguing pteropod known as a sea butterfly, or Clio pyramidata, allowing scientists to study the creature intact in the laboratory. Data are collected along the way, even when RSV Nuyina is on a resupply voyage. "The atmospheric and oceanographic underway data collected by RSV Nuyina are key for the Bureau of Meteorology, feeding into the national weather model ACCESS and global climate models," Miloslavich said.

The AAD is introducing a new Planning Framework that is designed to provide a structured and consistent approach for linking long term strategic priorities to the annual delivery of AAP activities in Antarctica and the Southern Ocean. The framework is intended to strengthen how we plan and sequence work across science, operations, infrastructure and station sustainment. It aims to establish clear decision points, align commitments to realistic capacity, and lock-in the Annual Delivery Plan for the AAP 12 months ahead of delivery. This will reduce late changes, improve certainty for all partners, and ensure regulatory, logistic and resource requirements for the AAP are factored in earlier. This is designed to reduce risk, including through clearer understanding of program lifecycle costs, which will allow for better AAP outcomes. Within this broader framework, the Integrated Planning Process (IPP) and the Season Operational Planning Process (SOPP) remain key components during the transition period. The IPP develops future season guidance (2-3 seasons ahead) assessing proposed activities against strategic priorities and within available capacity across multiple seasons. The SOPP uses the IPP guidance to focus on detailed planning for the upcoming year’s delivery, including vessel, aviation, station and field operations. Together, these processes ensure that all projects, operational requirements and regulatory obligations are assessed in a consistent way, aligned to strategic priorities and available capacity, and scheduled to maximise safety and efficiency.

As the Planning Framework is fully implemented, these processes will progressively consolidate into an integrated, planning cycle that provides clearer visibility and earlier certainty for delivering the Science Plan. Miloslavich's presentation outlined how Australian Antarctic Program campaigns and voyages planned for the next three seasons will contribute to the international collaborative program, Antarctica InSync. The Antarctica InSync program is endorsed by the UN Decade of Ocean Science for Sustainable Development, the Scientific Committee on Antarctic Research (SCAR) and the Council of Managers of National Antarctic Programs (COMNAP). Antarctica InSync will coordinate synchronized observations of ice, ocean, atmosphere, climate and ecosystems across the continent over two seasons (2027–28 and 2028–29) and aims to deliver the comprehensive evidence needed to inform global responses to climate change, biodiversity loss and human impact. "We have four strategic campaigns coming up in the next three years to support the delivery of the Science Decadal Strategy," Miloslavich said. On the continent, we will continue with the Million Year Ice Core (MYIC) project and the scientific activities carried out during the East Antarctic traverse from Casey to the MYIC project site high on the East Antarctic ice sheet. In the ocean, we will have the KaKE (krill and krill ecosystems) campaign in the 2027–28 season to assess the status of the krill-based ecosystem in the Mawson region.

The Marginal Ice Zone (MIZ) voyage in 2028–29 will study changing sea ice conditions at the time of the annual maximum in sea ice extent in September, a time when very few expeditions have gathered scientific information in Antarctica and the Southern Ocean. The ECCO voyage, the East Antarctic Ecosystems-CCAMLR, Climate and Ocean voyage, is scheduled for 2029–30 and will build on the work of the KaKE project and add scientific data to guide the design of Marine Protected Areas (MPAs) in East Antarctica. The interdisciplinary science program will support krill biomass assessments for the Commission for the Conservation of Marine Living Resources (CCAMLR), biodiversity and environmental monitoring to underpin the establishment of MPAs. It is anticipated that the Australian Antarctic Research Conference will be held again in 2028. "The research presented at this year's conference really showed the range and depth of Australia's expertise in Antarctic and Southern Ocean science," Miloslavich said. The key activities require planning and research coordination. They are not designed to be an exhaustive list of all science activities that will contribute to delivering the Science Strategy, particularly the Australia-based activities. The science sustainment, campaign, emerging priority, and other science requirement categories each involve a substantial amount of Australia-based science activity and capabilities to plan and prepare for focus years of field activity, and to subsequently realise the outcomes from field-based data gathered through the AAP. 

Rising glacier melt in Pakistan

 13,000+ glaciers melting put Pakistan on alert after deadly floods

Pakistan warned that accelerating glacier melt poses growing risks to lives, infrastructure and water security, as climate change intensifies extreme weather events across the country’s northern regions. Pakistan’s 13,032 documented glaciers and around 3,000 glacial lakes underscore the growing disaster risk facing communities in the country’s mountainous regions as climate change alters glaciers and increases the threat of glacial hazards. Country’s 13,000 glaciers feed Indus system are vital for agriculture, energy, water supply. 2025 flash floods and 2022 disaster highlight growing risks for the region from climate change. Environment scientist and glacier researcher Dr. Anees Ahmad warned that urgent investment in monitoring, early-warning systems, disaster infrastructure and public awareness was needed to reduce the risk of a major glacial disaster. Dr. Anees said Pakistan’s glaciers are concentrated across the Hindu Kush, Karakoram and Himalayan ranges, with around 30 glaciers covering areas of approximately 50 square kilometres each. The Hindu Kush region, particularly the border areas of Afghanistan and Chitral, contains more than 2,500 glaciers and around 180 glacial lakes, while the Himalayan region has more than 3,000 glaciers. The Karakoram alone contains around 10,000 square km's of glacial ice, according to the researcher.

The warning comes after a series of climate-linked disasters, including 2025 floods that the government estimates caused losses of Rs822 billion (around $2.9 billion) and claimed more than 1,000 lives across the country. Authorities say the deluge was driven in part by rising temperatures and changing glacier patterns in the Hindu Kush–Karakoram–Himalaya region. The latest events follow catastrophic floods, which killed more than 1,700 people and submerged large parts of the country, underscoring its vulnerability to climate shocks despite contributing minimally to global emissions. Climate change is accelerating glacier melt and increasing the likelihood of glacial lake outburst floods. The extreme heat and weather events witnessed in northern Pakistan in 2025, which led to flash floods, landslides, loss of lives and damage to infrastructure, served as a clear warning. Dr. Anees said the region faces multiple hazards because of steep and potentially unstable slopes, while rising temperatures are changing the country’s predominantly debris-covered glaciers.

Dr Anees called for continuous monitoring of glaciers and glacial lakes, installation of early-warning systems, creation of safe zones and stronger enforcement against construction along riverbeds and waterways. He also highlighted the shortage of weather stations in Pakistan and said several automated stations had been installed in high-altitude areas with support from the Italian high-altitude scientific research organization Ev-K2-CNR. Pakistan is home to more than 13,000 glaciers, the largest concentration outside the polar regions, which feed the Indus River system. Officials say shifts in glacier behavior are increasing the risk of glacial lake outburst floods, particularly in Gilgit-Baltistan and Khyber Pakhtunkhwa, where communities face growing exposure to sudden flooding and landslides. Water from these glaciers sustains millions of people downstream, irrigating farmland across the Indus basin and supporting both rural livelihoods and urban demand. The researcher cautioned against assessing glacier health solely through changes in surface area, arguing that glacier volume should also be measured to obtain a more comprehensive picture of climate-related changes.

Communities in glacial lake outburst flood (GLOF)-prone areas should not be allowed to rebuild homes in high-risk zones, while greater investment in research and monitoring would be necessary to improve disaster preparedness. Pakistan have taken steps to address the risks through policy measures, including the National Climate Change Policy 2021, the National Adaptation Plan 2023 and its commitments under international climate agreements. But still more regional and global cooperation, including improved data sharing, early warning systems and access to climate finance is required to help vulnerable mountain communities adapt to changing conditions. These glaciers are central to Pakistan’s water security and to the stability of the ecosystems that sustain millions. The choices Pakistan and world make today will shape the future of mountains and the wellbeing of generations that follow.

Evaluation of Low-Level Clouds, Temperature, and Surface Radiation

  Southern Ocean clouds are one of climate science's greatest challenges       

The Southern Ocean plays a pivotal role in regulating Earth's climate, yet the clouds that blanket this remote region remain among the least understood features in atmospheric science. By controlling both incoming sunlight and outgoing heat, these clouds strongly influence Earth's energy balance. Low-level clouds over the Southern Ocean (SO) exert a strong influence on surface radiation, yet their representation in reanalyses and climate models remains uncertain. Study evaluated cloud properties and surface radiative fluxes from ERA5, MERRA-2, and the CAM-ATRAS model using observations obtained over the SO by Japan's R/V Shirase. ERA5 and MERRA-2 overestimate the frequency of low-level clouds with a base below 1 km. Although CAM-ATRAS also overestimates very low clouds, it shows the best overall agreement with observations in cloud occurrence and phase. Despite the high frequency of low-level clouds, all data sets underestimate downward longwave (DLW) radiation. Cold bias and cloud phase bias likely reduce cloud-base emissivity and contribute to underestimated DLW radiation. Aerosol sensitivity experiments using CAM-ATRAS indicate that enhanced cloud condensation nuclei concentrations increase low-level cloud frequency but have a limited impact on surface radiative fluxes.

Even small errors in representing them can introduce significant uncertainties into weather forecasts, climate models and projections of future global warming, making them a long-standing challenge for climate scientists. To better understand why these clouds remain so difficult to simulate, researchers from the National Institute of Polar Research (Japan) and Nagoya University analyzed cloud observations collected during the 64th Japanese Antarctic Research Expedition (JARE64) aboard the research icebreaker R/V Shirase. Professor Jun Inoue explains, "Numerical models have been reported to exhibit limited skill in reproducing clouds. In particular, over the Southern Ocean and Antarctica, where cloud representation remains especially challenging, cloud-related biases have been shown to increase errors in the surface energy budget through biases in the radiative budget." Clouds over the Southern Ocean (SO) exert disproportionate influence on Earth's radiation budget by strongly modulating both shortwave and longwave radiative fluxes. Cloud macrophysical properties, such as horizontal and vertical cloud fractions, play critical roles in controlling downward shortwave (DSW) and downward longwave (DLW) radiation at the surface. Therefore, numerous studies have investigated the cloud fraction over the SO. Specifically, ice and liquid clouds produce distinct radiative effects because ice clouds have lower emissivity than liquid clouds, generally reflect less shortwave radiation, and emit weaker longwave radiation.

Many observational studies have been conducted focusing on the cloud phase over the SO. Although pure supercooled liquid water (SLW) freezes homogeneously below −38°C, ice nucleating particles (INPs), such as bioaerosols, mineral dust, and organic aerosols originating from both local and remote sources, can trigger freezing at much higher temperatures. Satellite and ship-based observations suggest that bioaerosols and other INPs contribute to mixed-phase and ice cloud formation at relatively high temperatures above −15°C over the SO and Antarctic coastal regions during spring and summer, which are seasons with high biological activity. Despite these findings, SLW clouds remain prevalent over the SO in summer, with occurrence frequencies of approximately 40% reported in active satellite products. Shipborne observations further indicate that SLW clouds are prevalent in the middle troposphere at temperatures higher than −25°C. Additionally, sulfate and organic aerosols, which comprise the greatest proportion of cloud condensation nuclei (CCN), play a central role in regulating low-level liquid cloud microphysics over the SO. Accordingly, many previous studies focused on aerosols and their role in low-level cloud formation over the SO. Numerical weather prediction and climate models are used widely to investigate cloud processes on the global scale. However, many models underestimate low-level cloud cover and the liquid water path, leading to excessive absorption of shortwave radiation at the surface over the SO. Such biases are commonly attributed to deficiencies in the representation of cloud phase and aerosol–cloud interactions, as demonstrated by comparisons with satellite products. The radiative effects of SO clouds remain a major source of uncertainty in climate projections. Indeed, substantial intermodel spread exists in the representation of cloud phase, and improved cloud phase representation with realistic INP concentrations can lead to reduced biases in cloud top radiative effects. Consequently, the SO remains one of the most challenging regions for cloud modeling, where persistent surface radiation biases have been identified in numerical models.

From December 2022 to March 2023, ship-based instruments continuously measured cloud properties, atmospheric temperature and humidity, surface radiation and aerosol concentrations, providing a comprehensive benchmark for evaluating model performance. The team evaluated two widely used atmospheric reanalysis data sets, ERA5 and MERRA-2, alongside the CAM-ATRAS climate model using observations throughout the expedition. Although all three data sets broadly captured cloud patterns over the Southern Ocean, important differences emerged. ERA5 and MERRA-2 consistently overestimated the occurrence of low-level clouds, whereas CAM-ATRAS most closely matched the observations, particularly in reproducing cloud occurrence and cloud phase. Surprisingly, despite simulating abundant low-level clouds, all three data sets underestimated the amount of downward longwave radiation reaching the surface. Comparison with observations showed that the reanalysis data sets contain higher aerosol concentrations than observed. Therefore, the researchers also conducted sensitivity experiments with CAM-ATRAS by increasing aerosol emissions over the Southern Hemisphere to examine how aerosols influence cloud formation and surface radiation. However, the aerosol sensitivity experiments further showed that increasing aerosol concentrations produced more low-level clouds but had only a limited effect on surface radiation.

The researchers traced this discrepancy to the physical properties of the simulated clouds rather than to cloud amount alone. In the models, clouds contained excessive ice, reducing the heat emitted toward the surface. However, these results demonstrate that biases in cloud representation alone cannot explain the underestimated DLW. Instead, the numerical models exhibit an inherent cold temperature bias, which also plays a role in the underestimation of DLW. These findings indicate that accurately representing both cloud phase and temperature is more important than simply reproducing cloud frequency when simulating the Southern Ocean's surface energy budget. By identifying the processes responsible for persistent cloud biases, the study provides valuable guidance for improving weather and climate models. Better representation of cloud microphysics, aerosol–cloud interactions and the background environment will help reduce uncertainties in simulations of Earth's energy balance, leading to more reliable predictions of future warming, sea ice change and climate variability. CAM-ATRAS explicitly simulates aerosol processes, including new particle formation, condensation, coagulation, activation to cloud droplets, aqueous-phase chemistry, dry and wet deposition, aerosol–radiation interactions, and aerosol–cloud interactions. Aerosols are represented using 12 size bins spanning diameters from 1 nm to 10 μm. Major aerosol species, including sulfate, black carbon, organic matter, SS, dust, marine organic aerosols, and bioaerosols are explicitly simulated, allowing detailed investigation of aerosol number concentrations and mixing states. INP number concentrations in clouds are calculated based on the simulated concentrations of dust, marine organic aerosols, and bioaerosols, the temperature dependence of ice-nucleation active site density per unit mass for each species, ambient temperature, and cloud fraction. These INP concentrations are then used to calculate ice nucleation within the cloud microphysical scheme.

In this study, the simulation period corresponding to the JARE64 cruise was used for analysis. Monthly sea surface temperature and sea ice distributions were prescribed as boundary conditions. The model was nudged toward MERRA-2 reanalysis fields for temperature and horizontal wind components in the free troposphere (pressure levels <800 hPa). The horizontal resolution was 0.9° × 1.25°, with 30 vertical layers extending from the surface to 40 km. In addition to the base simulation, a sensitivity simulation in which aerosol emissions over the SH were enhanced by two orders of magnitude (hereafter, referred to as the CAM-ATRAS SH × 100 experiment). The researchers emphasize that continued progress will require not only expanded observations of clouds across the Southern Ocean and Antarctica but also increased observations of fundamental atmospheric variables, particularly temperature, to reduce the cold bias in numerical models. As Assistant Professor Kazutoshi Sato notes, "Because observations over Antarctica remain sparse, numerical models still contain substantial uncertainties in their representation of the Antarctic atmosphere. Therefore, incorporating existing but currently underutilized observations into numerical models may provide an effective solution. For example, assimilating observations from the PANSY radar at Japan's Syowa Station, which are not yet routinely used in numerical weather prediction systems, could help reduce model biases and improve forecast accuracy." This study represents one of the most comprehensive observational evaluations of cloud and radiation simulations over the Southern Ocean using data collected during the JARE64 expedition.

During JARE64, clouds with a wide range of cloud base heights were observed over the SO and the Antarctic coastal regions. We calculated the frequency distribution of cloud base height over the entire observation period using 500-m vertical bins. Observations showed that clouds with a base height of below 1 km exhibit both primary and secondary peaks in occurrence frequency. Clouds with a base height in the middle troposphere were also frequently observed over the SO and Antarctic coastal regions. To compare cloud base height between observations and models, the modeled cloud base height was defined as the lowest model level at which the cloud liquid or ice mixing ratio exceeds 0.001 g kg−1. ERA5 overestimates the frequency of clouds with a base height of below 1 km. For CAM-ATRAS, although the frequency of clouds with a base height below 0.5 km is still overestimated, the occurrence frequency of clouds with a base height of below 1 km is closer to that of the observations than that of the two reanalysis data sets (ERA5 and MERRA-2). By revealing why current models struggle to reproduce these clouds and identifying the processes responsible for long-standing biases, the findings provide an important step toward more accurate weather forecasts, improved climate models and more confident projections of Earth's changing climate.

The National Institute of Polar Research (NIPR) was founded in 1973, is an inter-university research institute dedicated to advancing scientific research and observations in the Arctic and Antarctic regions. As one of the four institutes under the [Research Organization of Information and Systems (ROIS)], NIPR conducts comprehensive polar research through observation stations and international collaborations. The institute also promotes polar science by supporting collaborative research projects and providing access to scientific data, samples, and materials. NIPR remains Japan’s only institution devoted to comprehensive research activities in both polar regions. ROIS is a parent organization of four national institutes (National Institute of Polar Research, National Institute of Informatics, the Institute of Statistical Mathematics and National Institute of Genetics) and the Joint Support-Center for Data Science Research. It is ROIS's mission to promote integrated, cutting-edge research which goes beyond the barriers of these institutions, in addition to facilitating their research activities, as members of inter-university research institutes.

Hidden earthquakes at Antarctica’s Doomsday Glacier

 Seismic events have been detected beneath Antarctica’s Doomsday Glacier 

Hundreds of hidden earthquakes discovered beneath Antarctica, and they're happening in a very odd location. Antarctica was long thought to be seismically calm, but new technology makes it possible to detect unexpected types of earthquakes beneath the ice. Hundreds of previously overlooked seismic events have been detected beneath Antarctica, including 245 near the marine edge of the Thwaites Glacier. Many appear to be glacial earthquakes caused when huge icebergs break off, capsize and collide with the glacier. The surge in activity coincided with a period when Thwaites was flowing faster toward the ocean, hinting that changing ocean conditions may be destabilizing the ice. Massive icebergs break off from the glacier edge, roll over or capsize, and slam back into the main ice body. This violent collision sends strong mechanical vibrations and low-frequency seismic waves through the ground. These events stayed hidden because they do not produce the high-frequency waves typical of tectonic earthquakes, making them invisible to standard global sensor networks. Researchers analyzed seismic data recorded between 2010 and 2023.Findings: Out of 362 total glacial earthquakes detected across Antarctica during this period, 245 were concentrated right at the edge of the Doomsday Glacier. The study was conducted by Thanh-Son Pham from the Australian National University.

The surge in seismic activity lined up with periods when the glacier was flowing faster into the ocean. Thwaites Glacier holds enough ice to raise global sea levels significantly if it collapses completely, making these hidden tremors a crucial warning sign of structural change driven by warming ocean forces. Glacial earthquakes are a special type of earthquake generated in cold, icy regions. First discovered in the northern hemisphere more than 20 years ago, these quakes occur when huge chunks of ice fall from glaciers into the sea. Until now, only a very few have been found in the Antarctic. In a study, evidence found for hundreds of these quakes in Antarctica, mostly at the ocean end of the Thwaites Glacier, the so-called Doomsday Glacier which could send sea levels rising rapidly if it were to collapse. Artificial intelligence (AI) has revealed hundreds of previously unknown earthquakes beneath the East Antarctic Ice Sheet, including some in an unexpected place: in the middle of a tectonic plate, far from a plate boundary. The findings reveal that Antarctica is more seismically active than previously thought and new technologies can help to uncover hidden earthquakes in surprising locations.

In the new study, scientists used machine learning, a type of AI, to reanalyze seismic data taken from 49 seismic stations over the past two decades: one dataset from 2001 to 2004, and another from 2012 to 2015. The data revealed over 500 previously unrecognized earthquakes about 60 to 90 miles (100 to 150 km's) beneath David Glacier, which stretches nearly 700 miles (1,100 km's), bridging East and West Antarctica. This major outlet glacier drains about 4% of the East Antarctic Ice Sheet into the ocean, and its ice has thinned over the past several thousand years. A glacial earthquake is created when tall, thin icebergs fall off the end of a glacier into the ocean. When these icebergs capsize, they clash violently with the “mother” glacier. The clash generates strong mechanical ground vibrations, or seismic waves, which propagate thousands of km's from the origin. What makes glacial earthquakes unique is that they do not generate any high-frequency seismic waves. These waves play a vital role in the detection and location of typical seismic sources, such as earthquakes, volcanoes and nuclear explosions. Due to this difference, glacial earthquakes were only discovered relatively recently, despite other seismic sources having been documented routinely for several decades. Most glacial earthquakes detected so far have been located near the ends of glaciers in Greenland, the largest ice cap in the northern hemisphere. Earthquakes over 50 miles (80 km) deep are called intermediate-depth earthquakes. This type of earthquake is typically seen only at tectonic plate boundaries, specifically subduction zones, where one tectonic plate dives beneath another. Yet the study showed that these earthquakes are happening in the middle of the tectonic plate, far from active plate boundaries.

The Greenland glacial earthquakes are relatively large in magnitude. The largest ones are similar in size to those caused by nuclear tests conducted by North Korea in the past two decades. As such, they have been detected by a high-quality, continuously operating seismic monitoring network worldwide. The Greenland events vary with the seasons, occurring more often in late summer. They have also become more common in recent decades. The signs may be associated with a faster rate of global warming in the polar regions. Although Antarctica is the largest ice sheet on Earth, direct evidence of glacial earthquakes caused by capsizing icebergs there has been elusive. Most previous attempts to detect Antarctic glacial earthquakes used the worldwide network of seismic detectors. However, if Antarctic glacial earthquakes are of much lower magnitude than those in Greenland, the global network may not detect them. "The earthquakes occur where the cold, rigid crust and upper mantle beneath East Antarctica meets warmer, softer rock beneath West Antarctica, and this contrast creates an abrupt change in tectonic strength," Long Ho, a University of Alabama geologist and first author of the new paper, said. The detected earthquakes have magnitudes ranging from 1.6 to 3.5. The warm, buoyant material of the upper mantle extends beyond the edges of David Glacier from below, uplifting the edges of the nearby crust and bending them, and this concentrated stress causes the ground to shake, Ho explained. 

It was surprising to find so many earthquakes at these depths, far from plate boundaries, Ho said, but similar earthquakes may be occurring in other geographic regions and going unnoticed given their small magnitudes. AI could help to identify those hidden quakes by reanalyzing past seismic data. In the study, seismic stations in Antarctica itself to look for signs of these quakes. It turned up more than 360 glacier seismic events, most of which are not yet included in any earthquake catalogue. The events detected were in two clusters, near Thwaites and Pine Island glaciers. These glaciers have been the largest sources of sea-level rise from Antarctica. Thwaites Glacier is sometimes known as the Doomsday Glacier. If it were to collapse completely it would raise global sea levels by 3 metres, and it also has the potential to fall apart rapidly. About two-thirds of the events detected were located near the marine end of Thwaites. Most of these events are likely glacial earthquakes due to capsizing icebergs. The strongest driver of such events does not appear to be the annual oscillation of warm air temperatures which drives the seasonal behaviour of Greenland glacier earthquakes. Instead, the most prolific period of glacial earthquakes at Thwaites, between 2018 and 2020, coincides with a period of accelerated flow of the glacier’s ice tongue towards the sea. The ice-tongue speed-up period was independently confirmed by satellite observations. This speed-up could have been caused by ocean conditions, the effect of which is not yet well understood.

Deep earthquakes result from bending and flexure at the boundary between East and West Antarctica, beneath David Glacier. "As machine-learning tools continue to improve, they could reveal that deep, continental-interior earthquakes are more common than currently recognized," Ho said. "If so, the role of such events within the plate tectonics framework may need to be re-evaluated." The results also show that Antarctica is more dynamic than previously thought.  The data from this is now yielding new results as modern techniques have been developed to analyze the data. The findings suggest the short-term scale impact of ocean states on the stability of marine-terminating glaciers. This is worth further exploration to assess the potential contribution of the glacier to future sea-level rise. The second largest cluster of detections occurred near the Pine Island Glacier. However, these were consistently located 60–80 km's from the waterfront, so they are not likely to have been caused by capsizing icebergs. These events remain puzzling and require follow-up research. The detected earthquakes are not strong enough to threaten the overlying ice sheets or the Antarctic ecosystem, so the research team is not concerned about that. Antarctica’s sudden sea ice loss is one of the most extreme and confusing events in the modern climate record. Scientists now know why it's happening. The detection of glacial earthquakes associated with iceberg calving at Thwaites Glacier could help answer several important research questions. These include a fundamental question about the potential instability of the Thwaites Glacier due to the interaction of the ocean, ice and solid ground near where it meets the sea.

Better understanding may hold the key to resolving the current large uncertainty in the projected sea-level rise over the next couple of centuries. To explore how the enormous weight of the Antarctic Ice Sheet might contribute to the location of earthquakes, and how changes in the ice sheet could affect underlying seismic activity. It's still puzzling that seismic activity is concentrated at David Glacier rather than spread along the mountains in this region, the answer could be linked to the recent history of the ice sheet growing and shrinking, or to a longer history of the ice sheet eroding. However, work like this is continued and expanded, to help us understand the history and improve our understanding of possible futures.

Dark matter mapped by ghostly star

 First globular cluster stellar stream ever identified 

Most of the stars in our Milky Way galaxy sit neatly on a flat plane. But the space around our galaxy is much more chaotic. Rogue bands of stars called "stellar streams" orbit the Milky Way much like planets in our solar system orbit the sun. A ghostly stream of stars beyond the Milky Way is giving astronomers a new way to map the universe’s invisible dark matter. A faint ribbon of stars around a distant galaxy has become the first globular cluster stellar stream ever identified beyond the Milky Way. Because the stars trace the galaxy’s gravity, researchers used the stream to estimate how much invisible dark matter surrounds it and how that matter is distributed. The breakthrough offers astronomers a promising new way to investigate one of the universe’s greatest mysteries. Astronomers have long been fascinated by the possibility that stellar streams could indirectly reveal the presence of dark matter, that mysterious theorized substance which doesn't interact with light or normal matter, except via gravity. However, a new University of Washington study casts doubt on a leading theory linking dark matter and stellar streams and raises new questions about both galactic phenomena. "Dark matter makes up most of the mass in the universe and forms the scaffolding that galaxies grow on, but we still don't know what it is," said co-author Nora Shipp, a UW assistant professor of astronomy. "The Milky Way is one of the best laboratories we have for figuring that out, and stellar streams are one of the sharpest tools inside it."

For billions of years, an ancient cluster of stars has been gradually coming apart, shedding stars that now form a faint, narrow ribbon across space. That delicate structure is offering astronomers a new way to investigate one of the universe's biggest mysteries. An international research team, including an astrophysicist from Northwestern University, has identified the first stellar stream of this type ever observed outside the Milky Way. Astronomers have long predicted that such streams should exist around other galaxies, but their extreme faintness has made them difficult to detect. The newly discovered stream also offers scientists an unusual tool for studying dark matter, which remains one of the major unanswered questions in astrophysics. By analyzing the stream's shape, researchers reconstructed the gravitational field of its host galaxy and used that information to determine how unseen dark matter influenced the stars' paths. A stellar stream forms when a group of stars crashes into a galaxy and becomes ensnared by its gravity. As the stars orbit the galaxy, its gravity stretches the cluster into a long, thin filament of stars. Most galaxies host stellar streams, though the Milky Way's are the most visible to astronomers. In our galaxy, most stellar streams we can see are irregular, gaps and kinks interrupt an otherwise uniform smear of stars. Many astronomers believe those irregularities could signal the gravitational tug from small clumps of dark matter, called subhalos. If there are indeed subhalos sprinkled throughout the galaxy, studying the aberrations in stellar streams could teach us about the composition of dark matter.

The new study was an effort to understand the role that the host galaxy, rather than the dark matter clumps within it, plays in shaping stellar streams. Astronomers simulated four Milky Way-sized galaxies without any dark matter clumps, then peppered them with roughly 15,000 stellar streams. After five billion simulated years, the team observed irregularities in nearly every stellar stream. "In our simulations, the host galaxies alone caused the same kinds of irregularities that we observe in real stellar streams," said lead author Arpit Arora, a UW postdoctoral scholar in astronomy. "Now that we can predict what the host galaxy does on its own, we can start isolating the effects for which dark matter is responsible." The findings could eventually help scientists investigate how dark matter is distributed across many different galaxies and throughout the universe. "The stars in a stellar stream all travel along nearly the same orbit, and that orbit is shaped by the galaxy's gravity," said Northwestern's Tjitske Starkenburg. "By modeling that gravity, we can estimate the galaxy's total mass. We already know roughly how much of that mass comes from visible matter like stars, so the rest must be dark matter." Starkenburg, an expert in extragalactic astronomy, is a research assistant professor at Northwestern's Center for Interdisciplinary Exploration and Research in Astrophysics. 

The cause of the irregularities was the structure of the galaxies themselves. In each simulated galaxy, stars were spread somewhat unevenly across the disk, creating areas of greater and lesser density to mimic the composition of a real galaxy like ours. As the simulated streams of stars passed through denser regions of space, they were bent and torn by the irregular gravitational landscape. Arora expected the host galaxies to impart some irregularities on the streams, but the sheer number caught him off guard. "We found that almost all of the streams had some sort of structural variation," Arora said. "So this idea that streams are naturally thin and smooth wasn't really necessarily true."  The simulation generated wiggles, kinks, spurs, branches, gaps and clumps; some streams were totally torn apart by the gravitational froth of their host galaxies. Streams orbiting closer to the galactic core were thrown into dense, clumpy regions of space more often, where they acquired more irregularities. Out of the 15,000 streams spread across the four host galaxies, only 70 remained perfectly smooth after five billion years. The results might seem disheartening, but the UW team believes they chart a clear and exciting course for the future of dark matter research. Arora wants to include dark matter clumps in the next simulation to see whether they produce stellar stream irregularities that are distinct from those caused by the host galaxy alone.

Globular clusters are densely packed groups of stars held together by gravity. As one of these clusters travels around its host galaxy, the galaxy's gravitational pull can slowly strip stars away from it. Those stars do not simply scatter in every direction. Instead, they tend to continue along nearly the same orbital path, creating long, thin stellar streams that retain information about the gravitational forces they have experienced. Astronomers have identified dozens of streams produced by globular clusters inside the Milky Way. Until now, however, no comparable stream had been detected in another galaxy. Such structures are generally so faint that they disappear against the light of their host galaxies. There may also be opportunities to check simulations against new observations: the Simonyi Survey Telescope at the NSF-DOE Vera C. Rubin Observatory is expected to find many more stellar streams within our galaxy, which will help astronomers build a taxonomy of stream features and, hopefully, discover fingerprints of dark matter. "Sadly there's no magic wand to reveal the structure of dark matter," said James Davenport, a research assistant professor of astronomy at the UW. "Streams are complex systems, but they're still the most interesting way to study dark matter close to home." The breakthrough came through archival observations from NASA's Hubble Space Telescope presented by study coauthors David Sand and Catherine Fielder, both astronomers at the University of Arizona. While study coauthor David Hendel was examining images of the ultra-diffuse galaxy UGC 9050-Dw1 for their publication, he noticed a faint, narrow arc that looked like a stellar stream. UGC 9050-Dw1 lies roughly 115 million light-years from Earth. Because the galaxy contains relatively few stars, it provided an unusually dark background that made the dim stream easier to distinguish.

Although the current analysis centers on just one galaxy, the finding could lead to searches for similar stellar streams around many different types of galaxies. With a larger sample, astronomers may be able to learn much more about how dark matter behaves and how it is distributed. The importance of the discovery extends beyond finding the stream itself. Researchers have now shown for the first time that a globular cluster stellar stream can be used to investigate dark matter in a galaxy beyond the Milky Way. Dark matter accounts for roughly 85% of all matter in the universe. Because it does not emit or reflect light, astronomers cannot see it directly. Instead, they detect its effects through the gravitational influence it exerts on stars, galaxies, and other visible objects. Once the stream was identified, the team ran thousands of computer simulations. The researchers tested different combinations of globular cluster characteristics and possible dark matter distributions to determine which scenarios could reproduce the stream's observed appearance. The models that most closely matched the observations provided new estimates of UGC 9050-Dw1's total mass and showed how that mass is distributed throughout the galaxy. The results indicated that UGC 9050-Dw1 contains a large amount of dark matter, as astronomers had expected for an ultra-diffuse galaxy.

Future observatories could make these elusive structures much easier to find. The European Space Agency's Euclid mission and NASA's Nancy Grace Roman Space Telescope are designed to survey far larger regions of the sky than Hubble, increasing the likelihood that astronomers will detect stellar streams around additional galaxies. "It's exciting that we discovered a thin stellar stream around a galaxy other than our own with already-existing Hubble Space Telescope data and confirmed it with ground-based telescope data," Starkenburg said. "That makes it very promising for the new telescopes becoming available, including the Roman Space Telescope, which can see an area 100-times larger than that of the Hubble." Co-authors from the UW astronomy department include Peter Ferguson, a postdoctoral fellow; Videep Reddy, an undergraduate student; and Jack Kohm and Laurella Marin, graduate students. This research was funded by the Gordon and Betty Moore Foundation.