Through a new technique, scientists were able to use the James Webb Telescope to observe the thin rings of the asteroid Cariclus (or 10199 Chariklo), the largest known Centaur asteroid. Located more than 2 billion kilometers from the Sun, Cariclus is 250 km in diameter and its rings orbit 400 km from its center.
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Discovered in 1997, Chariclus is the smallest planetary body surrounded by rings known to date. Astronomers already knew that this asteroid is surrounded by rings of water ice, but now they have been able to better investigate these structures with James Webb.
For this, they had to wait for an occultation, taking advantage of Cariclus passing in front of a star, which temporarily blocks its light. The moment arrived in October last year.
On the 18th of that month, scientists used Webb’s Near-Infrared Camera (NIRCam) instrument to monitor the star Gaia DR3 6873519665992128512 and track small reductions in its brightness, signaling occultation as the asteroid passed. Then, the shadows cast by the Cariclus rings were clearly detected, signaling a new way of using Webb to study objects in the Solar System.
The rings were recorded exactly as scientists had hoped, and the data will help them study characteristics such as the thickness, sizes and colors of the particles that are there. “We hope to learn more about why this small body has rings and perhaps detect new ones,” said Pablo Santos-Sanz, a researcher who participated in the observations.
Shortly after the occultation, Webb observed the asteroid Cariclus again. This time, the objective was to collect data on the light reflected by it and its rings, producing a spectrum with three absorption bands of the frozen water. “The excellent quality of the Webb spectrum has revealed the clear signature of crystalline ice for the first time,” said Dean Hines, principal investigator of the second observation program.
Apparently, the rings are formed by small particles of frozen water mixed with ancient debris, coming from a frozen body that collided with Cariclus. Because the asteroid is so small and so far away, even the powerful James Webb telescope cannot capture direct images of the rings, separated from the main body.
In any case, the observation that Webb made of Cariclus and its rings may be just the first of many analyzes of small bodies located at great distances, providing even more knowledge about the objects that inhabit the outer reaches of the Solar System.
Source: Webb Telescope