Astronomers using the James Webb Space Telescope (JWST) have discovered that the ring system of Chariklo, a small solar system body, has changed over the last decade. The findings, published in the journal Science Advances, challenge previous scientific beliefs that small bodies possessed relatively stable rings.
Opposing Changes in Ring Opacity
Chariklo is a member of the Centaur family of asteroids, measuring approximately 155 miles (250 kilometers) wide. It orbits the sun between Saturn and Uranus at roughly 17 times the distance between Earth and the sun. While the body is diminutive, it possesses two thick rings.
To study these rings, a team led by researchers from the Institute of Astrophysics of Andalusia (IAA-CSIC) began observations in October 2022 using a technique called stellar occultation. This method measures the decrease in light from a star as an object passes in front of it. Because the JWST is not powerful enough to directly image the distant asteroid, researchers rely on these occultations to resolve the rings.
By comparing the JWST data with occultations recorded over the previous ten years, the team identified opposite shifts in the two rings. According to team leader Pablo Santos-Sanz, the inner ring has shown significantly higher opacity, while the outer ring has shown lower opacity.
Theories on Ring Composition and Stability
The cause of these changes is currently unknown, but Santos-Sanz noted that the results force a rethink of how these systems form, evolve, and maintain stability. One leading hypothesis to explain the stability and sharp edges of the rings is the existence of a small shepherd satellite sharing the orbit of the outer ring. Such a satellite could potentially shed debris to replenish the rings, though Santos-Sanz stated that no such satellite has been detected yet.
A computer model based on the JWST data suggests the two rings may have different compositions. Santos-Sanz indicated that the inner ring is likely composed of larger particles, while the outer ring is thought to be more dusty, though he described this specific part of the research as a work in progress.
The team believes the best way to verify these changes and rule out wavelength effects is to capture another occultation using visible light. This research adds to a growing list of small bodies with rings, including the trans-Neptunian object Quaoar, the dwarf planet Haumea, and Chiron, another body in the same category as Chariklo.
Technical Execution
The observations required extreme precision regarding the trajectory of the JWST around the L2 Lagrange point, located about 1 million miles (1.5 million kilometers) beyond Earth. According to team member Yücel Kilic, the project also relied on the European Space Agency’s Gaia mission to determine the exact position of the star and the orbit of Chariklo.
During the occultation, Chariklo traveled at approximately 5,600 miles per hour (2.5 kilometers per second) relative to the telescope. Researchers noted that this speed is relatively slow for solar system objects, which allowed the rings to be resolved in unprecedented detail.
Related reading