by By Will Dunham
WASHINGTON (Reuters) -Saturn’s rings are among the wonders of our solar system, spanning about 175,000 miles (280,000 kilometers) in diameter as they circle the giant planet. But smaller bodies in the solar system also have ring systems that are impressive in their own right, even if their size is not that large.
Scientists said that for the first time they have observed a ring system in the process of formation and evolution, consisting of four rings and diffuse material, surrounding a small icy body called Chiron, which orbits the Sun in the expanse between Saturn and Uranus.
Chiron is part of a class of objects called centaurs that populate the outer solar system between Jupiter and Neptune, showing characteristics of both asteroids and comets. Formally called “(2060) Chiron”, it has a diameter of about 200 kilometers (125 miles) and takes about 50 years to complete one orbit around the Sun. Centaurs are composed mainly of rock, water ice and complex organic compounds.
Since its discovery in 1977, astronomers have occasionally observed Chiron and have known for years that it was surrounded by some kind of material. In the new study, scientists obtained their best data on Chiron in 2023 using a telescope at the Pico dos Dias Observatory in Brazil, in addition to data from 2011, 2018 and 2022.
The researchers said these observations clearly showed that it is surrounded by well-defined rings: three dense rings located about 170 miles (273 km), 202 miles (325 km) and 272 miles (438 km) from Chiron’s center, and a fourth, about 870 miles (1,400 km) from the center. This appearance, discovered for the first time, is unusually far from Chiron and, they said, requires further observations to confirm its stability as a ring. The three inner rings are embedded in dust that swirls in a disk-like shape.
By comparing data from the different observations of Chiron, the researchers found significant changes in the ring system, clear evidence that the rings are evolving in real time, said Chrystian Luciano Pereira, a postdoctoral researcher at the National Observatory in Brazil and lead author of the study published in the Astrophysical Journal Letters.
“This provides a rare insight into how such structures arise and change,” Pereira said.
Chiron’s rings, Pereira added, are likely composed mainly of water ice mixed with small amounts of rocky material, like Saturn’s. Water ice may play a key role in the stability of ring systems because its physical properties allow particles to remain separated rather than coalesce into a moon.
Chiron occasionally exhibits comet-like activity, ejecting gas and dust into space. In 1993, Chiron even showed a small tail of material, as comets do.
The researchers said the rings may have been made from leftover material from a possible collision that destroyed a small moon of Chiron or from other space debris crashes, or from the material ejected by Chiron itself – or perhaps a combination of these factors.
“It is an evolving system that will help us understand the dynamical mechanisms that govern the creation of rings and satellites around small bodies, with possible implications for different types of disk dynamics in the universe,” says astronomer and co-author of the study Braga Ribas from the Federal University of Technology-Parana and the Interinstitutional Laboratory of e-Astronomy in Brazil.
All four of the solar system’s major outer planets – Jupiter, Saturn, Uranus and Neptune – have rings, with Saturn being the largest. But astronomers have discovered since 2014 that some of the smaller bodies have them too. Chiron brings that number to four, joining fellow centaur Chariklo and two icy worlds beyond Neptune: Haumea and Quaoar.
‘This diversity reminds us that ring formation is not exclusive to large planets. It is a universal process that can take place anywhere where the right physical conditions exist,” says Pereira.
A method called stellar occultation was used by a team made up of Brazilian, French and Spanish researchers to observe the rings. The researchers watched as Chiron passed in front of a distant star, temporarily blocking its light. By measuring how starlight dims from different locations on Earth, they were able to distinguish the environment around Chiron.
“We can reconstruct the shape and environment around the object with kilometer-scale precision,” Pereira said.
(Reporting by Will Dunham, Editing by Rosalba O’Brien)
