Webb reveals skull-shaped nebula and Uranus auroras

The James Webb Space Telescope delivered two striking discoveries in quick succession this month: the first three-dimensional map of Uranus's upper atmosphere and auroras, and detailed new infrared portraits of a little-known nebula that looks like a brain floating inside a transparent skull.

A New View of Uranus's Auroras

An international team led by Paola Tiranti, a PhD student at Northumbria University in England, used Webb's Near-Infrared Spectrograph (NIRSpec) to observe Uranus for 15 hours — nearly a full rotation of the planet — on January 19, 2025. The resulting data, published February 19 in Geophysical Research Letters, allowed scientists for the first time to map the temperature and density of ions stretching up to 5,000 kilometers above the planet's cloud tops.

The observations revealed two bright auroral bands near Uranus's magnetic poles, along with a distinct low-emission zone between them likely shaped by the planet's magnetic field lines. While the Hubble Space Telescope first captured images of auroras on Uranus in 2011, Webb's data represent the most detailed picture yet of how those auroras form and how the planet's tilted magnetic field influences them.

"This is the first time we've been able to see Uranus's upper atmosphere in three dimensions," Tiranti said in a statement released by the European Space Agency. "With Webb's sensitivity, we can trace how energy moves upward through the planet's atmosphere and even see the influence of its lopsided magnetic field."

​

The team also confirmed that Uranus's upper atmosphere continues to cool, a trend first observed in the early 1990s. Webb measured an average temperature of about 426 kelvins — roughly 150 degrees Celsius — lower than values recorded by ground-based telescopes or the Voyager 2 spacecraft, which performed the only close flyby of Uranus in 1986.

The "Exposed Cranium" Nebula

On February 25, NASA and ESA released Webb's new infrared images of nebula PMR 1, nicknamed the "Exposed Cranium" for its resemblance to a brain inside a translucent skull. The nebula is being created by an aging star shedding its outer layers, and Webb captured its features using both its NIRCam and MIRI instruments.

The images reveal distinct phases of the star's evolution — an outer shell of hydrogen blown off first, and a more structured inner cloud containing heavier gases. A dark lane running vertically through the nebula gives it the look of left and right brain hemispheres and may be linked to twin jets of material erupting from the central star. NASA's now-retired Spitzer Space Telescope first glimpsed the nebula in infrared more than a decade ago, but Webb's resolution has exposed detail that Spitzer could not resolve.

What Comes Next

Scientists say much remains unknown about PMR 1, including whether the dying star at its center is massive enough to end in a supernova or will instead cool into a dense white dwarf. As for Uranus, upcoming Webb observation cycles will monitor seasonal changes as the planet's north pole tilts toward the sun, with peak summer expected around 2028 to 2030. "By revealing Uranus's vertical structure in such detail, Webb is helping us understand the energy balance of the ice giants," Tiranti said. "This is a crucial step towards characterizing giant planets beyond our solar system."

New gravitational-wave method tackles cosmic expansion mystery

A team of astrophysicists from the University of Illinois Urbana-Champaign and the University of Chicago has developed a new technique to measure the rate at which the universe is expanding, leveraging the faint hum of gravitational waves produced by merging black holes across the cosmos. The research, accepted for publication in Physical Review Letters, introduces what the team calls the "stochastic siren" method — an approach that could help resolve one of the most persistent puzzles in modern cosmology.

A New Tool for Cosmology

The Hubble constant, which quantifies the universe's present-day expansion rate, has been measured using two broad approaches: observations of the early universe, such as the cosmic microwave background, and observations of the nearby universe, such as supernovae. These approaches yield values that disagree — roughly 67 km/s/Mpc from early-universe data versus approximately 73 km/s/Mpc from late-universe measurements — a discrepancy that has reached a statistical confidence exceeding five sigma.

The stochastic siren method offers an entirely independent path. Rather than relying solely on individually detected black hole mergers or electromagnetic observations, it incorporates information from the gravitational-wave background — a collective signal from the many distant black hole collisions too faint for current detectors to resolve individually.

"Because we are observing individual black hole collisions, we can determine the rates of those collisions happening across the universe," said Bryce Cousins, a physics graduate student at Illinois and lead author of the study. "Based on those rates, we expect there to be a lot more events that we can't observe, which is called the gravitational-wave background."

​The method's logic rests on a relationship between the expansion rate and spatial volume. A slower expansion rate implies a larger cosmic volume, which means more mergers and a stronger background signal. The current non-detection of the background therefore rules out the lowest expansion rates. When the team combined this constraint with data from resolved mergers recorded during the first three observing runs of the LIGO-Virgo-KAGRA Collaboration, they produced a more precise estimate of the Hubble constant than resolved mergers alone could provide.

A Promising Path Forward

Daniel Holz, a professor at the University of Chicago and co-author, called the technique "an entirely new tool for cosmology," adding that it opens "an exciting and completely new direction" for constraining the Hubble constant and other cosmological quantities.

​The gravitational-wave background is expected to be detected within the next six years as detector sensitivity improves. Even before that milestone, the stochastic siren method would progressively tighten the lower bound on the Hubble constant with each successive observing run that fails to detect the background — gradually probing the heart of the Hubble tension.

"This should pave the way for applying this method in the future as we continue to increase the sensitivity, better constrain the gravitational-wave background, and maybe even detect it," Cousins said. "By including that information, we expect to get better cosmological results and be closer to resolving the Hubble tension."

Astronomers detect radio echo of an unseen gamma-ray burst

 A team of astronomers has identified what they describe as the most convincing example yet of an "orphan afterglow" — the fading radio echo of a gamma-ray burst whose original explosion was never observed from Earth. The discovery, detailed in a paper accepted for publication in The Astrophysical Journal and posted to arXiv on February 24, opens a new window into some of the most powerful and elusive events in the universe.

The radio source, designated ASKAP J005512-255834, was found using the Australian SKA Pathfinder (ASKAP), a 36-antenna radio telescope in Western Australia. It sits in a small, actively star-forming galaxy roughly 1.7 billion light-years from Earth.

Ruling Out Alternatives

The signal was visible almost exclusively at radio wavelengths, with no counterpart in visible light or X-rays — a hallmark of an orphan afterglow. Follow-up observations spanning frequencies from 0.3 to 9 GHz, using instruments including the Australia Telescope Compact Array, the upgraded Giant Metrewave Radio Telescope, and MeerKAT, revealed an evolving spectrum consistent with synchrotron emission.

The team systematically ruled out other explanations, including pulsars, supernovae, and active galactic nuclei. Only two scenarios fit the observed behavior: the late-time afterglow of a long gamma-ray burst viewed off-axis, or a star being torn apart by an intermediate-mass black hole — a rare and still-hypothetical class of black holes.

Opening a Hidden Population

Either explanation would represent an exceptionally rare detection. The paper notes that if ASKAP J005512-255834 is confirmed as an orphan afterglow, it would be only the second such discovery made through radio observations. The team expressed hope that ASKAP and future radio survey instruments could uncover many more of these hidden events, offering a fuller census of gamma-ray bursts across the cosmos.

Scientists warn mega-constellations could devastate ozone layer

The race to fill low Earth orbit with vast fleets of satellites is raising alarms among atmospheric scientists, who warn that the mass burning of defunct spacecraft could damage the ozone layer and alter Earth's climate in ways that remain poorly understood. With SpaceX seeking permission to launch up to one million satellites and more than 1.23 million spacecraft now proposed worldwide, researchers and policymakers are calling for global regulation before the atmospheric consequences become irreversible.

An Atmosphere Turned 'Crematorium'

In a paper published this week in The Conversation, atmospheric chemist Laura Revell of the University of Canterbury, planetary astronomer Michele Bannister of the same institution, and astronomer Samantha Lawler of the University of Regina described the growing practice of deliberately burning up retired satellites as turning the atmosphere into "a crematorium for satellites". The authors estimated that a constellation of one million satellites could deposit a teragram — one billion kilograms — of alumina in the upper atmosphere, "enough, alongside launch emissions, to significantly alter atmospheric chemistry and heating in dramatic ways we do not yet understand".

Their warning comes weeks after SpaceX filed an application with the U.S. Federal Communications Commission on January 30 for a constellation of up to one million satellites intended to serve as orbital data centers for artificial intelligence. The proposal dwarfs the roughly 14,000 active satellites currently in orbit. Blue Origin announced its own 5,408-satellite TeraWave constellation on January 21, and China's Qianfan and Guowang programs are also advancing.

The Science of Satellite Pollution:

When satellites reenter the atmosphere, their aluminum structures burn and generate aluminum oxide nanoparticles. A 2024 study by University of Southern California researchers, published in Geophysical Research Letters, found that a single 250-kilogram satellite produces about 30 kilograms of aluminum oxide during reentry. In 2022, reentering satellites released an estimated 17 metric tons of these particles. If planned mega-constellations reach full deployment, that figure could exceed 360 metric tons annually — a 646 percent increase over natural levels.

Unlike chlorofluorocarbons, aluminum oxides are not consumed in the chemical reactions that destroy ozone; they act as catalysts, enabling ozone-depleting reactions to continue for decades. A separate 2025 study by CIRES and NOAA researchers found that by 2040, enough alumina could accumulate to heat parts of the mesosphere by as much as 1.5 degrees Celsius and reduce polar vortex wind speeds by about 10 percent. "We're really changing the composition of the stratosphere into a state that we've never seen before," said John Dykema, an applied physicist at Harvard.

A Regulatory Gap:

Despite the mounting evidence, the FCC is not required to conduct environmental reviews for satellite constellation licenses, relying on a categorical exclusion under the National Environmental Policy Act that has been in place since 1986. A 2022 Government Accountability Office report found the FCC had never assessed whether that exclusion remains appropriate for constellations of tens of thousands of satellites, and recommended the agency reconsider. Lawler and her co-authors argue that "there is no public mandate for a single company in one country to make changes on that scale to the planet's atmosphere," and are calling for a defined safe atmospheric carrying capacity for satellite launches and reentries before the industry scales further.

Brown dwarf's giant rings likely caused star's nine-month dimming

 A star more than 3,000 light-years from Earth nearly vanished from view for nine months, and astronomers now believe they have solved the mystery: an enormous ring system orbiting an unseen brown dwarf eclipsed the distant sun.

The star, known as ASASSN-24fw, had been stable for decades before it faded dramatically in late 2024, losing about 97 percent of its brightness before returning to normal in mid-2025. A study published Wednesday in Monthly Notices of the Royal Astronomical Society concludes that a brown dwarf—an object too large to be a planet but too small to sustain nuclear fusion like a star—likely passed in front of ASASSN-24fw, its colossal Saturn-like rings blocking almost all of the star's light.

A Rare Cosmic Alignment

The approximately 200-day dimming event ranks among the longest stellar eclipses ever recorded, according to the Royal Astronomical Society. Typical stellar eclipses last only days or weeks, making this months-long event exceptionally rare.

"Various models made by our group show that the most likely explanation for the dimming is a brown dwarf—an object heavier than a planet but lighter than a star—surrounded by a vast and dense ring system," said lead author Dr. Sarang Shah, a postdoctoral researcher at the Inter-University Centre for Astronomy and Astrophysics in Pune, India.

The ring system extends roughly 0.17 astronomical units from the companion object—about half the distance between the Sun and Mercury. The companion itself has a mass at least three times that of Jupiter.

Clues from the Past and Future

While investigating the dimming, the research team discovered that ASASSN-24fw is accompanied by a nearby red dwarf star. They also found evidence that the star has a circumstellar environment, possibly remnants of past planetary collisions, which is unusual for a star likely more than a billion years old.

Historical data revealed that ASASSN-24fw previously dimmed in 1981 and 1937, suggesting the companion completes an orbit approximately every 43 years. The next eclipse is not expected until around 2068.

"Large ring systems are expected around massive objects, but they are very difficult to observe directly to determine their characteristics," said co-author Dr. Jonathan Marshall, an independent researcher affiliated with Academia Sinica in Taiwan. "This rare event allows us to study such a complex system in remarkable detail."

New Astronomy Study Reveals How Titan and Saturn’s Rings Were Born

 Saturn's largest moon, Titan, and its spectacular ring system may both owe their existence to a single cataclysmic event — a collision between two ancient moons roughly 400 million years ago, according to a study led by SETI Institute scientist Matija Ćuk. The research, posted to the preprint server arXiv on February 11 and accepted for publication in The Planetary Science Journal, presents computer simulations suggesting the crash reshaped much of the Saturnian system.

A Two-Stage Catastrophe:

The hypothesis builds on data collected by NASA's Cassini spacecraft, which during its 13-year mission revealed that Saturn's rings are far younger than the planet itself and that Titan's orbit is shifting more rapidly than expected. A 2022 study had proposed that a lost moon, dubbed "Chrysalis," was ejected from Saturn's orbit and torn apart to form the rings. But when Ćuk's team ran simulations, they found that in 42 out of 60 cases, the most likely outcome was not ejection — but a direct collision with Titan.

The team proposes that two predecessors — a large "Proto-Titan" and a smaller "Proto-Hyperion" — merged violently, producing the Titan we observe today and scattering debris that coalesced into Saturn's small, irregularly shaped moon Hyperion. "We recognized that the Titan-Hyperion lock is relatively young, only a few hundred million years old," Ćuk said in a statement from the SETI Institute. "This dates to about the same period when the extra moon disappeared. Perhaps Hyperion did not survive this upheaval but resulted from it".

The collision itself did not directly create Saturn's rings. Instead, the researchers describe a chain reaction: Titan's newly eccentric orbit gradually destabilized smaller inner moons through gravitational resonances, sending them crashing into one another. The debris from those secondary collisions eventually settled into the ring system roughly 100 million years ago — consistent with independent age estimates.

Solving Multiple Mysteries at Once:

What makes the hypothesis compelling is its ability to address several long-standing puzzles simultaneously. It accounts for Titan's surprisingly few impact craters, which would have been erased in the merger. It explains the unusual orbital tilt of Saturn's distant moon Iapetus, which the simulations show was gravitationally disturbed by Proto-Hyperion before the crash. And it offers a reason why Saturn's axial wobble fell slightly out of sync with Neptune — the loss of the extra moon's mass changed Saturn's precession rate.

"This serves as a sort of grand unified theory that addresses all major issues," Ćuk told New Scientist. "We had some understanding of each problem individually, but this might illustrate how they interconnect in a single narrative that can be validated".

​

Sarah Hörst, a planetary scientist at Johns Hopkins University who was not involved in the study, said the work could "truly place Titan at the center of our understanding of the system today". Linda Spilker, a research scientist at NASA's Jet Propulsion Laboratory, called the findings "compelling evidence that Hyperion and Saturn's rings formed well after Saturn's inception".

What Comes Next:

The hypothesis remains to be peer-reviewed in its final published form. A definitive test may come from NASA's Dragonfly mission, a nuclear-powered rotorcraft scheduled to arrive at Titan in 2034. By analyzing the moon's surface geology and chemistry, Dragonfly could reveal whether Titan bears the scars of a violent origin half a billion years ago.

Studies find "Jupiter's moons may have formed with life's building blocks"

 Jupiter's four largest moons — Europa, Ganymede, Callisto, and Io — may not have formed as chemically barren worlds. Instead, they likely accumulated complex organic molecules essential for life during their very formation billions of years ago, according to a pair of complementary studies published in The Planetary Science Journal and Monthly Notices of the Royal Astronomical Society.

An international team led by scientists from Aix-Marseille University and Southwest Research Institute demonstrated that complex organic molecules, or COMs — carbon-rich compounds containing hydrogen, oxygen, and nitrogen — could have been forged within the proto solar nebula and Jupiter's circumplanetary disk, then incorporated into the moons as they took shape.

Two Pathways to Organic Chemistry

The studies trace two primary routes by which COMs could have reached the Galilean moons. In one paper, published in Monthly Notices of the Royal Astronomical Society and led by Tom Benest Couzinou of Aix-Marseille University, the team simulated 500 individual icy particles drifting through the protosolar nebula — the vast cloud of gas and dust that surrounded the young Sun. Their models found that when particles were released at distances around seven astronomical units from the Sun, roughly 45 percent of centimeter-sized particles formed COMs through thermal processing and subsequently reached Jupiter's orbital region within 300,000 years.

The companion paper, published in The Planetary Science Journal and led by Olivier Mousis — now at SwRI — examined how COMs could form locally within Jupiter's circumplanetary disk, the swirling environment of gas and dust where the moons coalesced. Heating of ices containing ammonia and carbon dioxide emerged as the dominant pathway for COM creation in this environment.

"Our findings suggest that Jupiter's moons did not form as chemically pristine worlds," Mousis said in an SwRI press release. "Instead, they may have accreted, or accumulated, a significant inventory of COMs at birth, providing a chemical foundation that could later interact with the liquid water in their interiors."

What It Means for Habitability

Europa, Ganymede, and Callisto are believed to harbor subsurface oceans beneath their icy crusts. An early inheritance of organic molecules means these moons may possess not only water and energy sources but also the chemical precursors that could drive prebiotic processes such as the formation of amino acids and nucleotides. The research indicates that Ganymede and Callisto, which likely formed under cooler conditions farther from Jupiter, may have retained even more of their primordial organic material than Europa.

Eyes on Jupiter

The findings arrive as two spacecraft are en route to test these predictions. NASA's Europa Clipper, launched in October 2024, is expected to reach the Jupiter system in April 2030 and will conduct 49 close flybys of Europa. ESA's JUICE mission, launched in April 2023, is on track for a July 2031 arrival after completing a Venus flyby in August 2025. Both carry instruments designed to detect organic compounds on the moons' surfaces and in their thin atmospheres — data that could confirm whether the chemical inheritance modeled in these studies left a detectable signature.