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.

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).