Astronomers using the NASA/ESA/CSA James Webb Space Telescope have captured the reflectance spectrum of the double-ringed centaur 10199 Chariklo and observed the shadows of starlight cast by Chariklo’s thin rings.
Chariklo is an icy, small body, but the largest member of a class known as the Centaurs.
It is 250-km in diameter and located between Saturn and Uranus about 2 billion km away.
In 2013, a team led by Dr. Felipe Braga-Ribas from Brazil’s Observatório Nacional/MCTI discovered that Chariklo hosts a system of two dense and narrow rings.
The astronomers had been watching a star as Chariklo passed in front of it, blocking the starlight as they had predicted. Astronomers call this phenomenon a stellar occultation.
To their surprise, the star blinked off and on again twice before disappearing behind Chariklo, and double-blinked again after the star reemerged.
The origin of these rings remains a mystery, but they may be the result of a collision that created a disk of debris.
In October 2022, Dr. Pablo Santos-Sanz from the Instituto de Astrofísica de Andalucía and colleagues found that Chariklo was on track for a similar occultation event.
They then used Webb’s Near-Infrared Camera (NIRCam) instrument to closely monitor a star called Gaia DR3 6873519665992128512, and watch for the tell-tale dips in brightness indicating an occultation had taken place.
The shadows produced by Chariklo’s rings were clearly detected, demonstrating a new way of using Webb to explore solar system objects.
The star shadow due to Chariklo itself tracked just out of Webb’s view. This appulse — the technical name for a close pass with no occultation — was exactly as had been predicted after the last Webb course trajectory maneuver.
The Webb occultation light curve, a graph of an object’s brightness over time, revealed that the observations were successful.
The rings were captured exactly as predicted. The occultation light curves will yield interesting new science…
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