When we think of asteroids, we often think of the main asteroid belt between Mars and Jupiter that contains the majority of the known asteroids in our solar system. However, our solar system hosts several other populations of asteroids and icy rocks, including the Jupiter Trojan asteroids that orbit in Jupiter’s orbit, and the icy bodies and comets of the Kuiper Belt. But there’s one population of asteroids that often gets overlooked called Centaurs, primarily because their orbits are not in a fixed location and instead whose orbits cross the orbits of the outer planets.
But one Centaur called Chariklo stands out not only because it’s the largest known Centaur with a radius of 125 kilometers (78 miles), but because it is the only Centaur to have a ring system, with Chariklo and its ring system discovered in 1997 and 2013, respectively. Now, an international team of more than two dozen researchers might have discovered how this ring system could have changed in recent years. As they discuss in a recent study published in Science Advances, the researchers present evidence that Chariklo’s two rings might be gaining and losing material.
To determine this, the researchers used a common technique called stellar occultation, which has been used for observations of Chariklo’s ring system in 2017 and 2022 using ground-based telescopes and NASA’s James Webb Space Telescope (JWST), respectively. The 2017 study established a baseline regarding the rings’ composition and sizes, while the 2022 study used JWST to observe Chariklo and its rings. It was determined that the inner ring was denser than the outer ring. While Chariklo is about 125 kilometers in radius, the inner ring (C1R) and outer ring (C2R) orbit about 265 kilometers (165 miles) and 280 kilometers (174 miles) from Chariklo’s surface, respectively.
For this most recent study, the researchers discovered the inner ring (C1R) had its opaqueness increase by more than 50 percent and the outer ring (C2R) had its opaqueness decrease by about 60 percent compared to the 2017 study. An object’s opaqueness is its ability for light to pass through it, with a fully transparent object being 0 percent opaque and a fully dark object being 100 percent opaque. Essentially, the inner ring was observed to be more dense than previous studies while the density of the outer ring was decreased. The researchers attribute this to material being replenished and lost for each respective ring.
The study notes, “More broadly, our occultation observations reveal previously unrecognized behavior in minor-body ring systems. The unexpected changes detected in Chariklo’s rings point to dynamical behavior that had remained entirely hidden until now, although they do not yet provide a definitive physical picture. Whether these changes primarily reflect temporal evolution, wavelength-dependent opacity, or a combination of both, their physical origin remains an open question, offering an unprecedented window into the physical processes shaping ring systems around minor bodies.”
Stellar occultations occur when a solar system object passes in front of a distant star and they can use the extremely small dip in starlight to observe an object’s size and even if it has rings. This works similarly to the transit method for identifying exoplanets, but while the transit method involves measuring a smaller object passing in front of a much larger star, stellar occultation involves measuring a very large object passing in front of a much smaller star. The researchers note how this study demonstrates JWST’s ability to use stellar occultation for studying solar system objects.
What new insights into Chariklo’s rings will scientists make in the coming years and decades? Only time will tell, and this is why we science!
As always, keep doing science & keep looking up!