SPACE/COSMOS
James Webb Space Telescope discovers that Chariklo’s invisible rings are changing
An international team led by the Institute of Astrophysics of Andalusia (IAA-CSIC) demonstrates for the first time that the two rings of this small Solar System body are changing in opposite directions
image:
Artistic view of the centaur Chariklo and its ring system. The bright point in the upper-right corner represents the Sun as seen from Chariklo’s distance.
view moreCredit: Credit: L. Maquet, Observatoire de Paris
Until just over a decade ago, ring systems were thought to be exclusive to the giant planets of the Solar System, such as Jupiter, Saturn, Uranus, and Neptune. However, in 2013, a small body barely 250 kilometers in diameter, located at nearly 17 times the Earth-Sun distance, joined this small group. The object is Chariklo, a small body orbiting between Saturn and Uranus, around which astronomers discovered two dense rings.
On October 18, 2022, the Institute of Astrophysics of Andalusia (IAA-CSIC) led an observation with the James Webb Space Telescope (JWST) to study Chariklo’s rings through a stellar occultation, a technique that measures the decrease in a star's light when an object passes in front of it. Now, a new study published in Science Advances and also led by the IAA-CSIC demonstrates, for the first time, that Chariklo’s ring system has undergone changes on timescales of just a few years.
“By comparing JWST observations with those obtained during other stellar occultations over the last decade, we discovered opposite changes in the two rings: while the inner ring shows significantly higher opacity, the outer ring shows lower opacity, ” explains Pablo Santos-Sanz, an IAA-CSIC researcher who leads the study.
This unexpected behavior indicates that Chariklo’s ring system is dynamic and may be subject to more complex physical processes than previously thought.
A SCIENTIFIC AND TECHNOLOGICAL MILESTONE
The study also represents a significant technological advance: the occultation by Chariklo was the first stellar occultation specifically predicted and planned for observation with JWST and successfully observed from the space telescope.
“Achieving this required knowing with extraordinary precision the orbit of Chariklo, the position of the star—thanks to ESA’s Gaia mission—and the trajectory of JWST itself around the L2 Lagrange point, a region of space located about 1.5 million kilometers beyond Earth, away from the Sun. JWST follows an orbit around this region that requires periodic corrections through station-keeping maneuvers,” notes Yücel Kilic, postdoctoral researcher at the IAA-CSIC and co-author of the study.
At the time of the occultation, Chariklo was moving relative to JWST at just 2.5 kilometers per second. This exceptionally low relative speed provided unprecedented spatial resolution for studying the structure of its rings. These rings are so narrow, and Chariklo is so far away, that they cannot be photographed directly, even with the James Webb Space Telescope or the largest ground-based telescopes. Stellar occultations allow astronomers to study them indirectly by measuring brief dips in a star's brightness as each ring passes in front of it.
Until now, scientists considered the rings around small bodies in the Solar System relatively stable. The changes detected in Chariklo challenge this view and suggest that these systems may be much more dynamic than previously thought. “Our results force us to rethink how they form, how they evolve, and what mechanisms maintain their stability. The ability to detect these changes opens a new window for understanding the evolution of these systems and, possibly, that of other ring systems in the Solar System,” says Santos-Sanz. The physical origin of the detected changes, however, remains an open question: they could reflect temporal evolution of the rings, differences related to the use of different filters, or a combination of both effects.
The Institute of Astrophysics of Andalusia (IAA-CSIC) led all phases of the study, from the project’s scientific design and the prediction of the occultation by Chariklo observed by JWST to the data analysis and the physical interpretation of the results. The IAA-CSIC team also played a fundamental role in ring modeling and the statistical analysis that demonstrated that the detected changes are real. The team carried out the work in collaboration with researchers from Spain, Brazil, France, Hungary, and the United States.
Schematic representation of the stellar occultation by Chariklo’s rings observed with the James Webb Space Telescope (JWST) on 18 October 2022. Comparison with previous occultations reveals opposite changes in the two rings: C1R shows a stronger signal, while C2R appears much weaker.
Journal
Science Advances
Method of Research
News article
Article Title
JWST stellar occultation reveals unexpected changes in Chariklo’s ring system’
Article Publication Date
9-Sep-2026
Soft and stretchy or rock solid? New modeling study sheds light on how the Earth got its moon
Simulations of the giant impact that is believed to have formed the moon need to take into account the geologic properties of the Earth and the moon's precursor
image:
New modeling studies that factor in geologic strength found fundamental changes in how the moon may have formed from the collision between a Mars-sized impactor and Earth. Simulations using older models that don’t factor in structural strength produce a debris disk (top), while the new models can produce an intact moon from the outset (bottom).
view moreCredit: NASA/JPL-CalTech/T. Pyle
For its size and location in the solar system, Earth has a surprisingly large moon. But how exactly the blue planet got its companion has vexed researchers for a long time. Researchers at the Southwest Research Institute and the University of Arizona used state-of-the-art computational techniques that revealed fundamental differences in how the moon may have formed from the collision between a Mars-sized object and Earth roughly 4.5 billion years ago.
Published in The Astrophysical Journal Letters, the results – for the first time – factor in the material strength of the two ancestral bodies and may change how researchers think the planetary collision happened. These impact simulations could change how researchers understand moon formation and may help constrain the timing of the event.
"We discovered that the preexisting geology of the Mars-sized proto-moon matters," said Adeene Denton, a former postdoctoral researcher at Lunar and Planetary Laboratory who is now at SwRI. "When you simulate the Earth and the moon as colliding bodies with geologic properties, it changes how the moon forms out of that impact – that's something we considered unnecessary before."
Earlier studies of the giant impact scenario include a foundational 2001 paper by Robin Canup, vice president of SwRI’s Solar System Science and Exploration Division in Boulder, Colorado, and Erik Asphaug, a professor at the Lunar and Planetary Laboratory and co-author of the current study. In the giant impact scenario, the debris from the collision of a Mars-sized body known as Theia with the early Earth obliterated Theia, scattering its remains into a disk around Earth. However, those simulations and subsequent giant impact modeling ignored material strength, which was thought to be insignificant for such high-energy events. Denton and her team revisited this hypothesis, using modern computational methods that incorporate temperature-dependent geologic strength for the first time.
"Because the collision was considered violent enough to melt and vaporize large portions of Earth and Theia, those previous papers assumed that it is okay to approximate them as fluids," Asphaug said. "Based on our new results, however, we think that it is time to reconsider that."
Denton revisited the hypothesis, for the first time using more advanced smoothed particle hydrodynamics simulations, or SPH, that take into account the structural strength of the bodies involved in the collision.
"It turns out material strength is really important when you're studying collisions between smaller bodies like asteroids, dwarf planets and moons," said Denton, who got the idea of applying the concept to Earth's moon while working on a previous paper about the formation of the Pluto-Charon system. "We weren’t sure if it would matter for our moon or not. When we did the simulations, we found it actually matters quite a bit."
This version of SPH, developed at the U of A and the University of Bern in Switzerland, uses a strength model that gives the bodies the kind of resistance to deformation that is expected for realistic geologic materials such as the rock and metals that would have made up Theia and the proto-Earth, or solid ice.
Hotter bodies are weaker than colder ones, and the team found that the different outcomes of Moon formation scenarios are sensitive to the temperatures of the colliding bodies. Some scenarios produce a fully intact moon within hours of the impact, while others result in a protolunar disk around the Earth that ultimately forms the moon over time. Because protoplanets generally start off hot and cool with age, this establishes an important new connection between the timing of the giant impact and the nature of the moon's initial state and assembly.
"Depending on how hot the Earth and moon are prior to the collision, the impact can destroy Theia and produce this massive disk of debris that eventually forms the moon," Denton said. "But when we used the same parameters as original impact modeling – down to the equal temperature structures inside both bodies – within around five hours, an intact moon emerged."
While intact moon outcomes have been seen in prior simulations, this work is the first to show that material strength and temperature play a central role in whether the moon forms intact or is assembled from material processed within a protolunar disk.
"These surprising and exciting new results imply a potential connection between the physical properties of the moon today, including perhaps its volatile content, and the thermal state of the Earth and Theia at the time of the giant impact," said Canup, who was not involved in the study. "This in turn might help scientists better constrain when the moon-forming event occurred."
The other conundrum remains the similarity of materials making up the Earth and the moon. As with prior models, explaining the close compositional makeup of the Earth and Moon remains an open scientific question.
"Because Earth and Mars formed in the same neighborhood of the solar system, they are like siblings," Denton said. "The moon and Earth are more like fraternal twins."
A possible explanation is that Theia and the proto-Earth formed from a common region of the solar system, while Mars, which is compositionally distinct from the Earth and Moon, formed farther away.
"We now know that the geophysical state of Earth and Theia play a fundamental role in shaping the outcome of the collision," said study co-author Namya Baijal, a doctoral student in Asphaug's group. "This gives us a new way to explore the conditions of the impact and what they might reveal about the moon's origin."
Watch the Moon formation simulations: https://www.youtube.com/watch?v=QAIRqc9dFHg
New modeling that accounts for material strength revealed fundamental changes in how the moon forms after a giant collision between a Mars-sized impactor and Earth. Simulations that neglect strength (top) produce a debris disk that forms the moon over time while those factoring in strength (bottom) can produce an intact moon right from the start.
Credit
Courtesy of SwRI
Journal
The Astrophysical Journal Letters
Method of Research
Computational simulation/modeling
Subject of Research
Not applicable
Article Title
Collisional Capture of an Intact Moon Depends on Strength
Article Publication Date
1-Sep-2026
No comments:
Post a Comment