JWST Spots Rings Around Asteroid In First Stellar Occultation

Chariklo is one of the few minor bodies in the Solar System known to have rings.

Artist's impression of Chariklo and its rings around the sun. Image credit: NASA, ESA, CSA, Leah Hustak (STScI)

Billions of kilometers beyond the orbit of Saturn, there’s a population of asteroids known as the Centaurs. The biggest among them is Chariklo, a rock 250 kilometers (160 miles) across that is known for also having two thin rings.


The discovery of these two rings happened thanks to a phenomenon called stellar occultation. When an object passes in front of a distant star, the amount of light dips. This approach has been used to discover moons and study atmospheres in the Solar System. And in the case of Chariklo, Felipe Braga-Ribas and collaborators saw five dips – four from the rings and one from the asteroid itself.


Researchers decided to do something similar with JWST too; and, as luck would have it, a star found itself almost right behind Chariklo last October. They were not perfectly aligned, so only the rings covered the star. This was the first stellar occultation for JWST and last October 22 went swimmingly.


Schematic view of the occulation and the light curve seen by JWST. Image credit: NASA, ESA, CSA, L. Hustak (STScI); Science: Pablo Santos-Sanz (IAA/CSIC), Nicolás Morales (IAA/CSIC), Bruno Morgado (UFRJ, ON/MCTI, LIneA).

“As we delve deeper into the data, we will explore whether we cleanly resolve the two rings. From the shapes of rings’ occultation light curves, we also will explore the rings’ thickness, the sizes and colors of the ring particles, and more. We hope gain insight into why this small body even has rings at all, and perhaps detect new fainter rings,” Pablo Santos-Sanz, from Instituto de Astrofísica de Andalucía in Granada, said in a statement.


This work is part of the Guaranteed Time Observations Program 1271 whose principal investigator is Santos-Sanz. JWST also looked at Chariklo directly and was able to observe the presence of water ice in a crystalline state. This suggests that the asteroid might be experiencing small collisions that either expose deeper pristine material or trigger crystallization processes. High-energy particles tend to mess with crystalline ice, so seeing it tells us that something must be going on to either form it again or uncover it.


JWST will continue to observe the object, and astronomers hope they will be able to more clearly distinguish between the contributions of the asteroid and the rings to the composition analysis in the future.

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