A Small World in the Outer Solar System Might Be Forming Rings Before Our Very Eyes

Material around Chiron, a small icy world in the far reaches of the solar system, may be taking shape into a ring system of its own. The rare event is unfolding in real time, giving astronomers a unique opportunity to witness the evolution of celestial bodies.

A team of scientists from Brazil observed initial hints of three rings forming around Chiron, transforming from a cloud of debris into a full-fledged system circling the unusual object. The recent findings were published in The Astrophysical Journal Letters and may be the first time astronomers are able to peek into the formation process of rings around an object.

Put a ring on it

While Saturn boasts the most complex ring system in the solar system, gas giants Jupiter, Neptune, and Uranus all have rings of their own. Aside from the giant planets, centaur Chariklo, and dwarf planets Haumea and Quaoar, they are the only small worlds in the solar system known to have rings as well. These rings are typically formed from the debris that is pulled into a planet’s gravitational field.

Discovered in 1977, Chiron was the first object identified between Saturn and Uranus that wasn’t a planet nor a moon. Instead, its discovery led to the creation of a new category of celestial objects known as centaurs. For years, the most intriguing mystery about Chiron has been whether the rocky world hosts a system of rings.

When astronomers observed Chiron as it passed in front of a distant star, the star’s light didn’t just dim once but rather a few extra times. This unusual pattern is leading astronomers to believe that Chiron may have a ring system, or perhaps a cometary tail or temporary cloud of debris surrounding it.

Using the Pico dos Dias Observatory in Brazil, the team of astronomers behind the new study observed Chiron in September 2023 as it crossed the path of a distant star. The team saw repeated dips in the star’s light and compared the recent data with observations of the centaur from 2011, 2018, and 2022.

The data revealed that Chiron is surrounded by three well-defined rings located around 170 miles (273 kilometers), 202 miles (325 kilometers), and 272 miles (438 kilometers) from the centaur, as well as a fourth, more distant one at a distance of about 870 miles (1,400 kilometers) away. The research team included first author Chrystian Luciano Pereira, a postdoctoral researcher at the National Observatory (ON/MCTI).

By comparing the recent observations to previous data, the team found that the ring system had experienced significant change and may be evolving in real time. Hints of the three main rings had appeared before, while the fourth one is relatively new and needs further observations to prove its ring status. The fourth ring exists beyond the Roche limit, a set distance within which a smaller celestial body would disintegrate and form a ring system around a larger body. Beyond the Roche limit, the material would coalesce to form a moon.

The team behind the study is hoping to capture more observations of Chiron as it passes in front of distant stars to help identify the nature of material surrounding it. If Chiron is indeed forming a ring system before our eyes, the small world will offer scientists a rare chance to understand how the mighty rings of Saturn and other planets took shape over time.