Heidi B. Hammel is a Webb interdisciplinary scientist leading Webbs Cycle 1 Guaranteed Time Observations (GTO) of the planetary system, consisting of Program 1271 as highlighted here. She is the vice president for science at the Association of Universities for Research in Astronomy (AURA) in Washington, D.C.
Dean Hines is an observatory researcher at the Space Telescope Science Institute (STScI) in Baltimore, Maryland and part of Webbs Mid-infrared Instrument Team. He is the primary detective for Webbs Guaranteed Time Observations Program 1272 “Kuiper Belt Science with JWST.”.
Noemí Pinilla-Alonso is an associate scientist in planetary science at the Florida Space Institute at the University of Central Florida and deputy primary scientist for the Arecibo Observatory. She is leading the science analysis of the Chariklo systems spectrum acquired by Webbs Near-infrared Spectrograph.
Pablo Santos-Sanz is a planetary researcher at the Instituto de Astrofísica de Andalucía (CSIC) and director of the Sierra Nevada Observatory in Granada, Spain. He is the principal detective for Webbs Guaranteed Time Observations Program 1271 “ToO TNOs: Unveiling the Kuiper belt by excellent occultations.”.
This artists impression shows how the rings might look from near the surface of Chariklo. Credit: NASA/JPL
In an observational feat of high accuracy, scientists utilized a new method with NASAs James Webb Space Telescope to capture the shadows of starlight cast by the thin rings of Chariklo. Chariklo is an icy, small body, but the largest of the known Centaur population, situated more than 2 billion miles away beyond the orbit of Saturn. Chariklo is just 160 miles (250 kilometers) or ~ 51 times smaller sized than Earth in diameter, and its rings orbit at a distance of about 250 miles (400 kilometers) from the center of the body.
We asked members of the science group observing Chariklo to tell us more about this unique system, the occultation technique, and what they gained from their Webb observations.
In 2013, Felipe Braga-Ribas and collaborators, using ground-based telescopes, discovered that Chariklo hosts a system of 2 thin rings. To their surprise, the star blinked off and on once again twice before disappearing behind Chariklo, and double-blinked again after the star reemerged. The blinking was triggered by two thin rings– the first rings ever detected around a little solar system things.
An occultation light curve from Webbs Near-infrared Camera (NIRCam) Instrument at 1.5 microns wavelength (F150W) shows the dips in brightness of the star (Gaia DR3 6873519665992128512) as Chariklos rings passed in front of it on Oct. 18. As seen in the illustration of the occultation event, the star did not pass behind Chariklo from Webbs perspective, but it did pass behind its rings. Quickly after the occultation, Webb targeted Chariklo once again, this time to gather observations of the sunlight reflected by Chariklo and its rings (GTO Program 1272). Most of the shown light in the spectrum is from Chariklo itself: Models suggest the observed ring area as seen from Webb during these observations is most likely one-fifth the area of the body itself. Pinilla-Alonso commented that “by observing Chariklo with Webb over a number of years as the seeing angle of the rings changes, we may be able to isolate the contribution from the rings themselves.”.
Pablo Santos-Sanz, from Instituto de Astrofísica de Andalucía in Granada, Spain, has actually an authorized “Target of Opportunity” program (program 1271) to attempt an occultation observation as part of Webbs solar system Guaranteed Time Observations (GTO) led by Heidi Hammel from the Association of Universities for Research in Astronomy. By exceptional good luck, we discovered that Chariklo was on track for simply such an occultation occasion in October 2022.
This video shows observations taken by NASAs James Webb Space Telescope of a star (fixed in the center of the video) as Chariklo passes in front of it. The video is made up of 63 private observations with Webbs Near-infrared Camera Instruments view at 1.5 microns wavelength (F150W) gotten over ~ 1 hour on Oct. 18. Careful analysis of the stars brightness exposes that the rings of the Chariklo system were plainly detected. Credit: NASA, ESA, CSA, Nicolás Morales (IAA/CSIC).
On October 18, we utilized Webbs Near-Infrared Camera (NIRCam) instrument to closely keep track of the star Gaia DR3 6873519665992128512, and look for the telltale dips in brightness showing an occultation had actually taken location. The shadows produced by Chariklos rings were plainly detected, demonstrating a new way of using Webb to check out solar system objects. The star shadow due to Chariklo itself tracked just out of Webbs view. This appulse (the trade name for a close pass with no occultation) was precisely as had been anticipated after the last Webb course trajectory maneuver.
The occultation light curves will yield intriguing new science for Chariklos rings. From the shapes of rings occultation light curves, we likewise will explore the rings thickness, the sizes and colors of the ring particles, and more. We hope gain insight into why this little body even has rings at all, and maybe find brand-new fainter rings.”.
An occultation light curve from Webbs Near-infrared Camera (NIRCam) Instrument at 1.5 microns wavelength (F150W) shows the dips in brightness of the star (Gaia DR3 6873519665992128512) as Chariklos rings passed in front of it on Oct. 18. As seen in the illustration of the occultation event, the star did not pass behind Chariklo from Webbs viewpoint, but it did pass behind its rings. Each dip actually represents the shadows of two rings around Chariklo, which are ~ 4 miles (6-7 kilometers) and ~ 2 miles (2-4 kilometers) broad, and separated by a space of 5.5 miles (9 kilometers). The 2 individual rings are not completely dealt with in each dip in this light curve. Image credit: NASA, ESA, CSA, Leah Hustak (STScI). Science: Pablo Santos-Sanz (IAA/CSIC), Nicolás Morales (IAA/CSIC), Bruno Morgado (UFRJ, ON/MCTI, LIneA).
The rings are most likely made up of little particles of water ice blended with dark material, debris from an icy body that collided with Chariklo in the past. Chariklo is too little and too far for even Webb to straight image the rings separated from the primary body, so occultations are the only tool to identify the rings by themselves.
Quickly after the occultation, Webb targeted Chariklo again, this time to gather observations of the sunlight reflected by Chariklo and its rings (GTO Program 1272). The spectrum of the system reveals 3 absorption bands of water ice in the Chariklo system. Noemí Pinilla-Alonso, who led Webbs spectroscopic observations of Chariklo, discussed: “Spectra from ground-based telescopes had hinted at this ice (Duffard et al. 2014), however the beautiful quality of the Webb spectrum revealed the clear signature of crystalline ice for the very first time.” Dean Hines, the principal private investigator of this 2nd GTO program, added: “Because high-energy particles change ice from crystalline into amorphous states, detection of crystalline ice shows that the Chariklo system experiences continuous micro-collisions that either expose beautiful product or trigger crystallization processes.”.
Webb recorded a spectrum with its Near-infrared Spectrograph (NIRSpec) of the Chariklo system on Oct. 31, soon after the occultation. This spectrum shows clear evidence for crystalline water ice, which was only hinted at by previous ground-based observations. Image credit: NASA, ESA, CSA, Leah Hustak (STScI). Science: Noemí Pinilla-Alonso (FSI/UCF), Ian Wong (STScI), Javier Licandro (IAC).
Many of the reflected light in the spectrum is from Chariklo itself: Models suggest the observed ring area as seen from Webb during these observations is most likely one-fifth the area of the body itself. Webbs high sensitivity, in combination with in-depth designs, might permit us to tease out the signature of the ring material distinct from that of Chariklo. Pinilla-Alonso commented that “by observing Chariklo with Webb over numerous years as the viewing angle of the rings changes, we may be able to separate the contribution from the rings themselves.”.
Our effective Webb occultation light curve and spectroscopic observations of Chariklo unlock to a new ways of characterizing little items in the distant planetary system in the coming years. With Webbs high sensitivity and infrared capability, scientists can utilize the unique science return offered by occultations, and boost these measurements with near-contemporaneous spectra. Such tools will be incredible properties to the researchers studying remote little bodies in our planetary system.
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