More than 99 percent of the upper atmosphere consists of electrically neutral gas known as the thermosphere. The term thermospheric density refers to the density of this neutral atmosphere between about 100 and 1000 kilometers above Earth’s surface. By comparison, the ionized gas of the ionosphere accounts for less than 1 percent of the atmosphere. Because ionized gas affects the way radio waves travel, the ionosphere is relatively straightforward to observe. Measuring conditions in the thermosphere is much more difficult.

A New Way to Observe the Thermosphere

Better measurements of thermospheric density could advance research into the upper atmosphere while also providing valuable information for space engineering. Motivated by both needs, researchers at Kyoto University developed a new technique for visualizing this difficult-to-observe region.

“This is a multidisciplinary study between space science and space engineering,” says corresponding author Mamoru Yamamoto. “Reading papers from both research fields, we realized that deeper dialogue between researchers from both fields is necessary.”

The researchers used publicly available orbital information from Starlink satellites and applied tomography, a technique commonly associated with medical imaging, to Earth’s upper atmosphere. By examining atmospheric drag through the gradual decay of satellite orbits, the team estimated thermospheric density around approximately 1,200 satellites flying at an altitude of 482 kilometers.

Building a Two-Dimensional Atmospheric Map

Using those measurements, the researchers produced a two-dimensional latitude-longitude snapshot of thermospheric density at an altitude of roughly 500 kilometers. According to the team, this represents the first tomographic analysis of its kind.

The resulting density patterns also showed strong consistency with observations from the European Space Agency’s SWARM satellites, which measure changes in atmospheric density along their orbital paths.

The work expands on an earlier study by the same team. In that research, scientists estimated how thermospheric density changed over time and altitude using general orbital information called Two-Line Element, or TLE, data from Starlink satellites. The new analysis adds another dimension by examining how density varies horizontally across latitude and longitude, revealing more of the thermosphere’s geographic structure.

Making Crowded Orbits Safer

The findings could have practical benefits as the number of objects orbiting Earth continues to grow. More accurate information about atmospheric density can improve predictions of satellite motion, helping reduce the chance of collisions between satellites and between satellites and space debris.

The technique could also eventually support near-real-time measurements of atmospheric density around satellites. Such monitoring could improve space weather forecasting and contribute to safer, more dependable satellite operations in the future.

Glial cells play essential supporting and nourishing roles in the brain. One type, known as astrocytes because of their star-shaped appearance, is especially important for healthy neuron function. Astrocytes provide nerve cells with nutrients, help control blood flow, and support the overall health of brain tissue.

Scientists had long thought that once astrocytes were destroyed, the adult brain could not fully replace them. This loss can occur after brain injuries and in autoimmune diseases such as the rare neuromyelitis optica spectrum disorder, in which the body’s own antibodies attack and destroy astrocytes.

Specialized Astrocytes Rebuild Damaged Brain Tissue

A study led by co-lead authors Marina Herwerth and Matthias Wyss of the Institute of Pharmacology and Toxicology at the University of Zurich (UZH) challenges that long-standing view. The research team, headed by Bruno Weber, identified a specialized population of “regenerative” astrocytes in the brains of living mice.

These cells gather around the edges of damaged brain regions and help rebuild the lost astrocyte network. “The findings of our study reveal a previously unknown ability of the adult brain to repair itself. They point toward new ways of supporting recovery from ailments involving the loss of astrocytes,” Weber says.

New Cell Nuclei Travel Into Damaged Areas

To follow the repair process, the researchers used two-photon microscopy to observe the brains of living mice in real time for several weeks. They also tracked which genes became active in different regions of the brain. Together, these methods allowed the team to identify the astrocytes responsible for restoring injured tissue.

The regenerative cells do more than simply divide. They also carry out an unusual process in which newly created nuclei from daughter cells travel considerable distances through the astrocytes toward the damaged region. As Weber explains, “they send the newly formed nuclei of their daughter cells gliding across long distances to repopulate the damaged area of the brain and knit the astrocyte network back together.”

New Targets for Brain Regeneration

The finding that cell nuclei can move through the long extensions of adult astrocytes into injured tissue adds a new dimension to scientists’ understanding of how the brain organizes its own repair after certain types of damage.

If researchers eventually learn how to selectively activate these repair mechanisms, they may be able to promote more effective restoration of damaged brain tissue, rebuild astrocyte networks, and improve recovery from certain brain disorders.

The team also identified many genes and signaling pathways that become temporarily active while the repair process is underway. These biological signals may provide potential targets for future efforts to influence regeneration after disease or injury.

“We were able to identify numerous genes and signaling pathways that are temporarily activated during repair. They could serve as starting points in the future for influencing post-disease and -injury regeneration processes,” Weber stresses.

The research focused on keratin, a natural structural protein that can be extracted from wool. When tested in a living animal, the material supported bone regeneration and produced new tissue that more closely resembled healthy, natural bone than tissue formed using the current gold standard material.

Researchers at King’s College London tested the wool-based keratin in animal models and found that it could help direct new bone growth across damaged areas.

“We are really excited to show for the first time how a wool-based material has been successfully tested in a living animal to repair bones,” said Dr. Sherif Elsharkawy at King’s Faculty of Dentistry, Oral & Craniofacial Sciences.

Wool Offers a Sustainable Source for Bone Repair

Beyond its potential medical benefits, wool could offer an important sustainability advantage. It is a naturally derived material and is often discarded as waste by the farming industry, giving it potential as both a renewable and scalable resource.

For decades, collagen has served as the gold standard scaffold in many regenerative medical and dental applications. These scaffolds act as protective barriers during healing, keeping soft tissue from interfering with the damaged area while giving new bone space to grow.

Collagen, however, has several drawbacks. The material is relatively weak and may degrade too quickly, which can limit its usefulness when repairing bones that need to bear weight or withstand force. Extracting collagen can also be complicated and costly.

“From a research perspective this is a major milestone. It positions keratin as a potential new class of regenerative biomaterial that could challenge the long-standing reliance on collagen,” said Dr. Sherif Elsharkawy.

Testing Wool Keratin as a Bone Scaffold

To investigate whether keratin could overcome some of these limitations, the researchers created membranes from keratin extracted from wool. They chemically treated the material to produce scaffolds designed to remain stable and durable.

The membranes were first tested with human bone cells in the laboratory. The cells grew well on the material and showed clear signs associated with healthy bone formation.

Researchers then moved to animal testing. They implanted the keratin membranes into rats with skull defects that were large enough that they would not normally heal on their own. Over the following weeks, the team tracked how effectively the membranes supported new bone growth across the damaged regions.

Keratin Produced More Naturally Organized Bone

The results revealed an important difference between keratin and collagen. Collagen membranes generated a greater amount of bone overall, but the bone formed with the keratin scaffolds was more organized and structurally secure. Its fibers were also better aligned, giving the new tissue a closer resemblance to natural, healthy bone.

The keratin membranes also remained stable during the healing process and integrated smoothly with the surrounding tissue. Both characteristics are important if the material is eventually to be considered for practical medical applications.

“We’ve effectively demonstrated the technology in an animal model, which makes this much more than an early materials concept. It shows that keratin can support bone regeneration in a living biological system, bringing the technology significantly closer to use in real patients,” concludes Dr. Elsharkawy.

The Hubble Space Telescope previously observed the nebula in 2000, imaging the lion face-shaped target in visible light. Those observations highlighted its distinctive appearance, including a “mane” made up of hazy structures resembling comet tails. Webb’s high-resolution instruments now provide an even sharper look at the same object.

Webb Reveals Hidden Details in the Lion Nebula

In broad terms, the Lion Nebula looks similar in Webb’s infrared observations to the structure seen earlier by Hubble. Webb observed it with both NIRCam (Near Infrared Camera) and MIRI (Mid Infrared Instrument). Its infrared capabilities, however, bring out features that are harder to see in visible light, including dense concentrations of dust and hazy regions of ionized gas.

The gas and dust now forming the nebula have been evolving for several thousand years. Even today, those materials continue to shift and change.

At the center of this activity are the remains of a dying star. In the lion-shaped appearance of the nebula, this stellar remnant resembles a small button nose. Despite its modest appearance, the star’s radiation and energy are responsible for driving many of the complex structures surrounding it.

How a Dying Star Created the Cosmic Lion

Very massive stars can end their lives in supernova explosions, but such events are relatively uncommon. Most stars in the Universe have lower masses, including the star that created NGC 2392.

When a lower-mass star reaches the point where nuclear reactions in its core can no longer support it, the star becomes unstable and begins to pulsate. As this happens, it sheds its outer layers into space. Those expelled layers form expanding shells of gas and dust known as a planetary nebula (stars at this life stage are responsible for producing much of the Universe’s observable dust).

Radiation from the exposed stellar core pushes the discarded material outward. What remains at the center is an extremely hot stellar core called a white dwarf.

In the Lion Nebula, the oxygen-rich central star has died and left behind a white dwarf that is effectively “cooking” the nebula from within. Its intense radiation is creating a bubble of ionized gas that makes up the lion’s recognizable face.

As this bubble grows, it sweeps outward and destroys dust in its path. Astronomers are still working to understand why this swept-up gas forms such complicated arrangements of rings and shells, structures that are commonly seen in planetary nebulae.

A Glowing Mane of Dust and Gas

The lion’s mane corresponds to the inner region of a dust shell illuminated by the white dwarf at the center. Within it are structures that resemble tufts of hair or comet-like tails.

These features are actually compact clumps of dust that have managed to withstand radiation from the stellar core. By blocking some of that radiation, the dense clumps also shield material located behind them.

Webb’s observations effectively “freezes” the planetary nebula at one moment in its long evolution, but the consequences of the star’s death are continuing. Gas and dust will keep traveling away from the central stellar remnant, gradually changing the nebula’s appearance.

Astronomers estimate that the Lion Nebula will eventually disperse in approximately 10,000 years. On astronomical timescales, that is a relatively brief period.

More information

Webb is the largest and most powerful telescope ever launched into space. Under an international collaboration agreement, ESA supplied the telescope’s launch service using the Ariane 5 launch vehicle.

Working with its partners, ESA was responsible for developing and qualifying the Ariane 5 adaptations needed for the Webb mission and for procuring the launch service from Arianespace. ESA also contributed the workhorse spectrograph NIRSpec and 50% of the mid-infrared instrument MIRI, which was designed and built by a consortium of nationally funded European Institutes (The MIRI European Consortium) in partnership with JPL and the University of Arizona.

Webb is an international partnership between NASA, ESA, and the Canadian Space Agency (CSA).

When electrons are restricted to a two-dimensional plane and interact strongly enough, they can begin behaving very differently from ordinary electrons. Instead of moving independently, they arrange themselves into a repeating pattern similar to the orderly structure of atoms in a conventional crystal.

This unusual arrangement is called a Wigner crystal. Scientists have studied it for decades because the crystal structure is created by interactions between the electrons themselves rather than by the underlying structure of the material containing them.

While researchers have already detected Wigner crystals in a variety of physical systems, understanding what happens inside them has been much harder. Scientists have struggled to directly investigate how their electrons move collectively, interact with one another, and react to outside disturbances.

Using Light to Probe a Wigner Crystal

In a study published in Nature Physics, experimental researchers led by Professor Tomasz Smoleński at the University of Basel examined a single atomic layer of tungsten diselenide that had been cooled to only a few degrees above absolute zero.

The team illuminated the material and carefully analyzed the light reflected from it. Those measurements revealed previously unseen optical features that contain information about the collective behavior of electrons inside the Wigner crystal.

The signals emerge from interactions between the ordered electrons and excitations created in the material by light, known as excitons. Together, these components form hybrid quasiparticles called Wigner crystal polarons. These quasiparticles serve as highly sensitive optical probes that can reveal both the crystal itself and the collective motion occurring within it.

“Our measurements show that light can do more than simply detect the presence of this exotic state — it can reveal how the state behaves internally,” says first author Dr. Lujun Wang from the University of Basel, who carried out the experiments together with Ferdinand Menzel, a PhD student in Smoleński’s group.

“This gives us a powerful new tool for studying collective excitations of electronic crystals that would otherwise be extremely difficult to access,” adds Smoleński.

Electron Interactions Shape the Optical Signals

The researchers also discovered that the strength of the interactions between electrons influences the optical signatures they observed. That connection could make the signals especially useful for investigating strongly correlated systems, where the behavior of the material emerges from interactions among many particles rather than from individual particles acting on their own.

To account for the experimental findings, a theoretical team led by Professor Michael Knap at the Technical University of Munich (TUM) developed a model describing the formation of Wigner crystal polarons. Their work explains how these quasiparticles arise through the coupling of optically generated excitons with the collective movement of electrons in the crystal.

A New View of Strongly Correlated Quantum Matter

“What is particularly exciting is that these signals carry information not only about how the electrons are arranged, but also about their quantum dynamics,” explains Fabian Pichler, a PhD student at TUM. “This allows us to connect the experimental observations directly to the underlying many-body physics.”

The findings suggest that atomically thin materials could provide an especially useful platform for observing how electrons move collectively within ordered quantum states. By making these hidden dynamics easier to study, the approach could help scientists develop a deeper understanding of strongly correlated matter and the complex behavior that emerges when many particles interact.

“By observing the propagation of radio waves, we can create an image of the surroundings and of persons who are present,” says Professor Thorsten Strufe from KASTEL, KIT’s Institute of Information Security and Dependability. “This works similar to a normal camera, the difference being that in our case, radio waves instead of light waves are used for the recognition,” explains the cybersecurity expert.

Because the technique analyzes radio waves moving through a space, a person does not need to have a phone, smartwatch, or other WiFi enabled device with them. “Thus, it does not matter whether you carry a WiFi device on you or not.”

Even turning off your own device would not necessarily prevent the system from working. “It’s sufficient that other WiFi devices in your surroundings are active.”

Ordinary WiFi Routers Could Become Surveillance Tools

The researchers say the findings reveal a potentially serious privacy risk because WiFi networks are already widespread in homes, offices, restaurants, and public spaces.

“This technology turns every router into a potential means for surveillance,” warns Julian Todt from KASTEL. “If you regularly pass by a café that operates a WiFi network, you could be identified there without noticing it and be recognized later — for example by public authorities or companies.”

There are currently simpler ways for intelligence agencies or cybercriminals to monitor people, Felix Morsbach notes. Those methods can include gaining access to existing CCTV systems or connected video doorbells.

“However, the omnipresent wireless networks might become a nearly comprehensive surveillance infrastructure with one concerning property: they are invisible and raise no suspicion.”

That possibility makes WiFi based monitoring especially notable. Unlike a visible security camera, a wireless network normally gives people no obvious indication that its radio signals could potentially be used to recognize who is nearby.

No Special Surveillance Hardware Is Needed

Earlier approaches to sensing people through wireless signals have often relied on specialized equipment or more complex measurements. Some techniques, for example, use LIDAR sensors, which measure distances by sending out light and analyzing the reflected signal.

Other WiFi based approaches use channel state information (CSI). This refers to measurements showing how a wireless radio signal changes as it travels through an environment and reflects from walls, furniture, people, and other objects.

The new technique does not require that kind of specialized hardware. According to the researchers, a standard WiFi device is enough.

The method takes advantage of normal communications produced by legitimate users connected to a WLAN. WLAN is another term for a wireless local area network, essentially the WiFi network operating within a home, office, café, or similar location.

Connected devices routinely send information back to the router to help optimize wireless communication. These signals, known as beamforming feedback information (BFI), are transmitted without encryption, meaning that anyone within range can potentially read them.

By analyzing that information, the system can generate images of people from multiple viewpoints. Those images can then be used to determine a person’s identity.

Once the machine learning model has already been trained to recognize individuals, the identification process takes only a few seconds.

Researchers Achieved Almost 100% Identification Accuracy

The team tested the technique in a study involving 197 participants. Their system was able to infer people’s identities with almost 100% accuracy, regardless of the viewing perspective or the way a person walked.

“The technology is powerful, but at the same time entails risks to our fundamental rights, especially to privacy,” emphasizes Strufe.

The researchers are particularly concerned about how such technology could be used in authoritarian countries. They warn that WiFi based identification could potentially be applied to monitor protesters or other groups without the obvious surveillance infrastructure associated with conventional cameras.

Because wireless networks are already so common, the researchers argue that privacy protections should be built into future WiFi technology before these capabilities become easier to exploit at scale.

They are therefore calling for protective measures and privacy safeguards to be incorporated into the forthcoming IEEE 802.11bf WiFi standard.

Funding and Publication

The project was funded under the Helmholtz “Engineering Secure Systems” topic.

The researchers presented their results at the “ACM Conference on Computer and Communications Security” (CCS) in Taipei.