Astronomers using the James Webb Space Telescope have discovered that the ring system surrounding the tiny solar system body Chariklo is changing over time. Researchers report opposite shifts in the asteroid’s two rings, challenging long-held assumptions about the stability of ring systems around small celestial bodies.
Chariklo orbits the sun between Saturn and Uranus at roughly 17 times the distance between Earth and the sun. Despite measuring only about 155 miles across, this member of the Centaur family of asteroids possesses two distinct rings. While giant planets like Saturn, Uranus, Neptune, and Jupiter are famous for their ring systems, the existence of rings around diminutive bodies such as Chariklo and the smaller Chiron shows that small worlds can develop complex structures.
Initial discovery of Chariklo’s rings occurred in 2013, establishing that minor bodies could harbor such features. Now, observations conducted with the James Webb Space Telescope reveal that these rings are more dynamic and active than scientists previously understood.
Stellar Occultation and Decade-Long Changes
A research team led by scientists from the Institute of Astrophysics of Andalusia began observing Chariklo with the space telescope in October 2022. The team utilized a technique known as stellar occultation, which measures the drop in light from a distant star as an object passes directly in front of it. During the observed occultation, Chariklo traveled at approximately 5,600 miles per hour relative to the telescope. This low relative speed allowed researchers to resolve the asteroid’s rings in unprecedented detail, because direct imaging of the distant body remains impossible even for advanced space observatories.
By comparing the recent space telescope data with occultation measurements gathered over the preceding ten years, the researchers noted that the inner ring shows significantly higher opacity, while the outer ring shows lower opacity. These contrasting transformations force a reassessment of how minor ring systems behave.
Rethinking Stability and Orbital Mechanics
Scientists historically considered the ring systems of small solar system bodies to be relatively stable over time. The observed shifts demonstrate that complex physical processes govern these rings, forcing researchers to reevaluate current models of formation and maintenance.
The leading hypothesis to explain the rings’ sharp edges, stability, and ongoing material replenishment points to a ghost moon—an undetected shepherd satellite sharing the outer ring’s orbit. Computer models based on telescope data suggest a compositional difference between the two rings as well. Researchers believe the inner ring consists of larger particles, while the outer ring contains more dust. However, investigators emphasize that these compositional models remain a work in progress.
Precision Engineering at the L2 Lagrange Point
Obtaining data of this caliber required extraordinary positional accuracy. Researchers needed precise calculations of Chariklo’s orbit, stellar positions supplied by the European Space Agency’s Gaia mission, and the exact trajectory of the telescope itself.
Achieving this required knowing with extraordinary precision the orbit of Chariklo, the position of the star, thanks to the European Space Agency’s Gaia mission, and the trajectory of JWST itself around the L2 Lagrange point, a region of space located about 1 million miles (1.
Yücel Kilic, team member at the Institute of Astrophysics of Andalusia
Operating in this distant region requires continuous adjustments. The telescope maintains its station through periodic trajectory corrections, an engineering feat that enables high-precision celestial measurements.
Broader Implications and Future Observations
The findings extend beyond a single asteroid. Rings are now confirmed around other minor bodies, including the dwarf planet Haumea, the trans-Neptunian object Quaoar, and another Centaur body named Chiron. While giant planet rings like Saturn’s D ring and Neptune’s Adams arcs are known to shift over months and years, the published study in Science Advances establishes that small solar system bodies experience similar evolutionary changes.
To verify whether the observed shifts stem from actual physical changes or wavelength-dependent scattering effects, the research team is actively searching for new stellar occultations that can be captured using visible light.