What will Webb's observation of Chariklo tell us about this asteroid? James Webb Space Telescope Observes Astonishing Ring System of Chariklo Asteroid

The star (Gaia DR3 6873519665992128512) experienced dips in brightness on October 18 as Chariklo's rings crossed in front of it, as shown in an occultation light curve from Webb's Near-infrared Camera (NIRCam) Instrument at 1.5 microns wavelength (F150W). The star did not pass behind Chariklo from Webb's perspective, but it did pass behind its rings, as can be seen in the image of the occultation event. Each dip actually represents the shadows of two rings that surround Chariklo and are approximately 4 miles (6-7 kilometers) and 2 miles (2-4 kilometers) wide, with a distance of 5.5 miles separating them (9 kilometers). Each dip in this light curve does not completely resolve the two separate rings. Credit: NASA, ESA, CSA, Leah Hustak (STScI). Science: Pablo Santos-Sanz (IAA/CSIC), Nicolás Morales (IAA/CSIC), Bruno Morgado (UFRJ, ON/MCTI, LIneA)

January 25, 2022

The thin rings of Chariklo cast shadows of starlight, which were captured by researchers using a new technique with NASA's James Webb Space Telescope. The largest known population of Centaurs is represented by Chariklo, an icy, tiny body that lies more than 2 billion kilometers outside of Saturn's orbit. Chariklo's diameter is only 160 miles (250 kilometers), which is 51 times smaller than that of Earth, and its rings are located roughly 250 miles (400 kilometers) from the body's core.

Using ground-based telescopes, Felipe Braga-Ribas and associates found that Chariklo is home to a system of two thin rings in 2013. Only around massive planets like Jupiter and Neptune had such rings been anticipated. As expected, Chariklo passed in front of a star, blocking its light as the astronomers watched it. This occurrence is known as an occultation by astronomers. To their surprise, the star double-blinked once more after emerging from behind Chariklo then twice more before blinking off and on again twice more. The first rings ever discovered surrounding a minor solar system object were the two thin rings that were responsible for the blinking.

In order to attempt an occultation observation as part of the Webb solar system Guaranteed Time Observations (GTO) led by Heidi Hammel from the Association of Universities for Research in Astronomy, Pablo Santos-Sanz from the Instituto de Astrofsica de Andaluca in Granada, Spain, has been granted a "Target of Opportunity" program (program 1271). By an amazing stroke of fate, we found that Chariklo was on schedule for a similar occultation event in October 2022. This was the first attempt at a star occultation with Webb. Finding and improving the predictions for this uncommon event required a lot of effort.

On October 18, we closely monitored the star Gaia DR3 6873519665992128512 using Webb's Near-Infrared Camera (NIRCam) sensor to look for the telltale dips in brightness indicating an occultation had occurred. Clear evidence of the shadows cast by Chariklo's rings was found, illuminating a fresh method for using Webb to investigate solar system objects. The star shadow caused by Chariklo moved out of Webb's line of sight. This appulse, or near pass without an occultation, occurred exactly as had been foreseen following the previous Webb course trajectory maneuver.

The observations were successful, as shown by the Webb occultation light curve, a graph of an object's brightness over time! As expected, the rings were successfully captured. For Chariklo's rings, the occultation light curves will produce intriguing new scientific findings. "As we go deeper into the data, we will study whether we cleanly resolve the two rings," Santos-Sanz said. We will investigate the thickness of the rings, the sizes and colors of the ring particles, and more from the shapes of the occultation light curves of rings. We hope to learn more about why this little body has rings at all and potentially find some new, fainter rings.

On October 31, immediately after the occultation, Webb's Near-infrared Spectrograph (NIRSpec) recorded a spectrum of the Chariklo system. This spectrum clearly demonstrates the presence of crystalline water ice, which previous ground-based observations had only suggested. Credit: NASA, ESA, CSA, Leah Hustak (STScI). Science: Noemí Pinilla-Alonso (FSI/UCF), Ian Wong (STScI), Javier Licandro (IAC).

The remnants of an icy mass that once crashed with Chariklo make up the rings, which are most likely made up of microscopic pieces of water ice combined with black stuff. Occultations are the only method available to describe the rings separately because Chariklo is too small and too far away for even Webb to directly photograph them. 

Soon after the occultation, Webb retargeted Chariklo to gather data on how the star and its rings reflected sunlight (GTO Program 1272). Three bands of water ice in the Chariklo system can be seen in the system's spectrum. Spectra from ground-based telescopes previously hinted at this ice (Duffard et al. 2014), but the exquisite quality of the Webb spectrum revealed the unequivocal trace of crystalline ice for the first time, according to Noem Pinilla-Alonso, who oversaw Webb's spectroscopic observations of Chariklo. The second GTO program's principal investigator, Dean Hines, added: "Detection of crystalline ice indicates that the Chariklo system experiences continuous micro-collisions that either expose pristine material or initiate crystallization processes." This is because high-energy particles cause ice to change from crystalline into amorphous states.

Models estimate the observed ring area as seen from Webb during these observations is likely one-fifth the area of the body itself, with the majority of the reflected light in the spectrum coming from Chariklo itself. With the use of comprehensive models and Webb's great sensitivity, we might be able to distinguish the ring material's unique signature from Chariklo's. As the viewing angle of the rings changes with time, Pinilla-Alonso said, "By watching Chariklo with Webb, we may be able to identify the contribution from the rings themselves."

Source - NASA

October 31, 2022

Today James Webb Telescope has targeted Chariklo, an asteroid with rings. We should soon have amazing findings from these observations of Chariklo by the James Webb Space Telescope. The largest confirmed centaur is Chariklo (small body of the outer Solar System). It passes close to Uranus' orbit as it revolves around the Sun between Saturn and Uranus. Chariklo became the first minor planet known to have rings when, on March 26, 2014, astronomers announced the discovery of two rings (known as the rivers Oiapoque and Chu) around it by studying a star occultation. A photometric analysis conducted in 2001 was unable to identify a precise rotational period. Chariklo has been observed to have water ice, which may actually be found in its rings, based on infrared measurements.

Centaurs are space objects that have their origins in the Kuiper belt. Due to their dynamically unstable orbits, they could leave the Solar System, collide with a planet or the Sun, or change into a short-period comet. Compared to Nessus, Chiron, and Pholus, Chariklo has a more stable orbit. The orbital half-life of Chariklo, which is predicted to be roughly 10.3 Myr, is within 0.09 AU of Uranus' 4:3 resonance. According to orbital calculations of twenty Chariklo clones, it will take around 35,000 years for Chariklo to begin routinely approaching Uranus at a distance of 3 AU (450 Gm). Chariklo had an apparent magnitude of +17.7 during the 2003–2004 perihelic oppositions . Chariklo was 14.8 AU from the Sun as of 2014.

Surprisingly, observations at numerous locations in South America, including ESO's La Silla Observatory, have revealed that the distant asteroid Chariklo is encircled by two constricting rings. This object is just the fifth body in the Solar System to have rings, after the considerably larger planets Jupiter, Saturn, Uranus, and Neptune. It is by far the smallest object to have rings ever discovered. These rings' origin is unknown, although it's possible that a collision that produced a disc of debris is what gave rise to them.

It will be exciting to see what additional details James Webb Telescope will provide on Chariklo and its rings.