JWST Observations Reveal Unexplained Transformations in Chariklo’s Rings

Recent observations from the James Webb Space Telescope (JWST) indicate that the rings encircling a peculiar minor planet situated between Saturn and Uranus appear noticeably different from previous measurements.

These rings orbit Chariklo, classified as a centaur—a unique celestial body exhibiting traits of both asteroids and comets. Measuring approximately 250 kilometers (400 miles) in diameter, Chariklo is among a vast population of small objects residing in the outer solar system.

Astronomers initially identified Chariklo’s rings in 2013, marking the first time such a feature was found on a small solar system body. Subsequent ground-based observations occurred in 2014 and 2017. However, when JWST examined the centaur in 2022, a decade of time had seemingly altered its appearance, according to findings published on September 9 in the journal Science Advances.

“By comparing JWST observations with those obtained… 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,” explained Pablo Santos-Sanz, a researcher at the Institute of Astrophysics of Andalusia and the study’s lead author.

The exact cause of these transformations remains unknown, though researchers proposed three potential explanations. First, JWST’s superior resolution may have resolved both denser and sparser regions within the rings that older instruments could not detect. Second, the physical composition or the grains comprising the rings might have shifted. Finally, the telescope may have detected “grains with wavelength-dependent optical properties,” capturing variations in grain size and composition that account for the observed differences.

Santos-Sanz noted that these findings imply ringed minor bodies—even those isolated from the gravitational pull of larger planets—may undergo more dynamic changes than previously assumed. “Our results force us to rethink how they form, how they evolve, and what mechanisms maintain their stability,” he stated.

To verify the new JWST data, the researchers suggested a follow-up observation during Chariklo’s next stellar occultation, particularly to confirm the shifting opacities of the inner and outer rings.

“These observations would help disentangle temporal evolution from wavelength-dependent scattering effects, and clarify the physical processes shaping Chariklo’s rings,” the team wrote in their study.

A Milestone for JWST

The recent study also represents a milestone for the space telescope: it is the first time scientists have scheduled a JWST observation specifically to capture a stellar occultation. This requires timing the telescope’s view to the exact moment Chariklo passes in front of a distant background star.

Historically, all observations of Chariklo’s rings—whether from Earth or space—have relied on stellar occultations. Because the rings are too faint for direct imaging, astronomers must analyze the fluctuations in brightness as the centaur transits a star. This technique is also employed by JWST to study the atmospheres of distant exoplanets.

Chariklo’s relatively slow speed against JWST’s line of sight—1.5 miles per second (2.5 kilometers per second)—enabled high-resolution imaging of the rings. To precisely time the occultation, scientists utilized data from the European Space Agency’s Gaia mission, which maps the positions and motions of over two billion stars. They also accounted for JWST’s orbit, located roughly 1.5 million kilometers (930,000 miles) from Earth, facing away from the sun. The researchers emphasized that executing this observation demanded “extreme precision.”

Source link