RINGS DIVERSITY AROUND SMALL SOLAR SYSTEM BODIES: DISCOVERIES AND DETECTION LIMITS

Abstract

The first detection of a ring system through stellar occultation, a significant milestone in the history of planetary science, occurred in 1977. Then, astronomers unexpectedly discovered Uranus’s rings while studying the planet’s atmosphere. This discovery was followed by a similar one in 1984 when Neptune’s rings were detected as arcs using the same method. A decade ago, a ring system was identified around the Centaur object (10199) Chariklo, marking the first instance of such a feature in a small body beyond the giant planets. This discovery suggested that ring systems might be more common among small Solar System bodies than previously believed, as evidenced by subsequent findings around the dwarf planet Haumea and the indications of rings or cometary material around the Centaur (2060) Chiron. Considering that some authors suggest cometary activity might be related to the presence of rings, we sounded the vicinity of small bodies in the outer solar system, using the stellar occultation technique to search for signs of confined material. A stellar occultation happens when an object is observed blocking a distant star’s light during a certain time interval. Observing the star’s light before, during, and after the occultation lets us gather detailed information about the object’s astrometric position, size, shape, atmosphere, and ring systems. In terms of spatial resolution, this highly precise method can reveal fine details that are otherwise difficult to detect from ground-based observations, making it invaluable for studying distant and faint Small Solar System Objects. The Centaurs Objects (60558) 174P/Echeclus, 29P/Schwassman-Wachamnn 1 (29P), and (2060) Chiron exhibited regular outbursts, making them ideal targets for the search for confined material. We first examined light curves from stellar occultations of the active Centaur Echeclus observed between 2019 and 2021. While no features indicative of surrounding material were detected, strong detection limits were established, and the physical properties of Echeclus were derived. We observed the first stellar occultation by 29P in December 2022 and were able to find indications of confined material symmetrically distributed around the object. Occultation observations of Chiron were conducted in 2018, 2019, and 2022 to characterize its structures over time. The 2019 event, being the first multi-chord observation of this Centaur, allowed us to constrain its tri-axial dimensions. The 2022 observations confirmed previously proposed structures and revealed significant property variations, such as width and optical depth. A recent stellar occultation of Chiron in 2023 is still under analysis, but the high-resolution data obtained at Observatório do Pico dos Dias may solve ongoing questions about Chiron’s environment. The greatest finding came after discovering a ring beyond the Roche limit around the Trans- Neptunian Object (50000) Quaoar. We conducted an observation campaign to further characterize this ring in 2022. Our analysis revealed the presence of a second ring around Quaoar, much closer to the main body but also located beyond the Roche limit. This thesis presents the methods developed to search for, characterize, and place upper limits on detecting confined material around SSSO. We present observational evidence that material ejections alone are not capable of forming rings. Due to the diversity of the confined structures’ location in the Solar System and their properties presented here, it is clearer that the formation of rings around small bodies can only result from a combination of factors, such as (primordial) collisions or ejection processes, allied with a favorable dynamical environment around the main body. Our findings and physical properties of the studied objects are presented in association with the respective research papers.