James Webb Reveals Chariklo Thin Rings Using High-Precision Techniques – All Pages

Illustration of the distant asteroid Chariklo and its two dense and narrow rings.

Nationalgeographic.co.id—In high-precision observations, scientists used a new technique with NASA’s James Webb Space Telescope to capture the shadows of starlight cast by Chariklo’s thin rings.

Chariklo is a small icy body, but the largest of the known population of Centaurs. It lies more than 1.6 billion kilometers beyond Saturn’s orbit. Chariklo is only 250 kilometers in diameter or ~51 times smaller than Earth, and its rings orbit at a distance of about 400 kilometers from the center of its body.

We asked the members of the science team who observed Chariklo to tell us more about this unique system, the occultation technique, and what they learned from their Webb observations, the researchers said.

In 2013, Felipe Braga-Ribas and his collaborators, using ground-based telescopes, discovered that Chariklo has a system of two thin rings. Such rings are thought to only exist around large planets such as Jupiter and Neptune.

Astronomers had been observing a star as Chariklo passed in front of it, blocking the starlight as they had expected. Astronomers call this phenomenon an occultation. To their surprise, the star flashed repeatedly twice before disappearing behind Chariklo, and blinked two more times after it reappeared. The twinkling is caused by two thin rings – the first rings ever detected around a small solar system object.

Pablo Santos-Sanz, of the Instituto de Astrofísica de Andalucía in Granada, Spain, has an approved “Target of Opportunity” program (program 1271) to attempt occultation observations as part of the Webb solar system program Guaranteed Time Observations (GTO) led by Heidi Hammel of the Association of Universities for Research in Astronomy.

By some stroke of luck, they found that Chariklo was on track for such an occultation event in October 2022. This was the first stellar occultation experiment with Webb. A lot of hard work went into identifying and perfecting the predictions for this unusual event.

On October 18, researchers used Webb’s Near-Infrared Camera (NIRCam) instrument to closely monitor the star Gaia DR3 6873519665992128512, and observed a dip in brightness that would indicate an occultation.

The image produced by the Chariklo ring is clearly detectable. It demonstrates a new way of using Webb to explore solar system objects. The shadows of the stars due to Chariklo himself traced beyond Webb’s view. This appulse (technical name for close pass without occultation) was exactly what had been predicted after the last Webb pass maneuver.

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Webb’s occult light curve, a graph of an object’s brightness over time, reveals that the observation was a success! Ring captured exactly as expected. Occult light curves yield exciting new science for Chariklo’s rings.

“As we delve deeper into the data, we will explore whether we resolve both rings cleanly. From the shape of the ring’s occultation light curve, we will also explore ring thickness, ring particle size and color, and more,” explains Santos-Sanz. We hope to gain insight into why small objects like this could have rings, and perhaps detect new, fainter rings.”

The rings may consist of tiny particles of water ice mixed with dark matter, debris from an icy body that collided with Chariklo in the past. Chariklo was too small and too far away for even Webb to directly imagine the rings being separate from the main body. So occultation is the only tool to characterize the rings themselves.

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