The Ultraviolet Imaging Spectrograph instrument onboard NASA’s Cassini spacecraft observed 41 solar occultations by Saturn’s rings. Now, planetary researchers have compiled complete catalogs of these occultations as high-level data products.
NASA’s Cassini spacecraft in orbit around Saturn. Image credit: NASA / JPL-Caltech.
Cassini’s Ultraviolet Imaging Spectrograph (UVIS) was uniquely sensitive to some of the smallest particles in Saturn’s rings, particularly with the observations it made in the extreme ultraviolet wavelength.
To determine the size of the ring particles, the instrument observed them when it was pointed at the Sun, looking through the rings in what is known as a solar occultation.
The ring particles partially blocked the path of the light, providing a direct measurement of the optical depth, a key parameter for determining the size and composition of the ring particles.
“For nearly two decades, NASA’s Cassini spacecraft shared the wonders of Saturn and its family of icy moons and signature rings, but we still don’t definitively know the origins of the ring system,” said Dr. Stephanie Jarmak, a researcher at the Southwest Research Institute.
“Evidence indicates that the rings are relatively young and could have formed from the destruction of an icy satellite or a comet.”
“However, to support any one origin theory, we need to have a good idea of the size of particles making up the rings.”
“Given the wavelength of the light coming from the Sun, these observations gave us insight into the smallest particle sizes with Saturn’s rings,” she added.
“UVIS can detect dust particles at the micron level, helping us understand the origin, collisional activity and destruction of the ring particles within the system.”
According to the researchers, during an occultation, light emitted by a background source, such as the Sun, is absorbed and scattered by the particles in the light’s path.
The amount of light blocked by ring particles provides a direct measurement of the ring optical depth.
Including optical depth is vital to understanding the structure of the rings.
The authors measured the optical depth as a function of the viewing geometry, which refers to the observation angles of the ring system with respect to Cassini.
As light passing through the rings changes at various angles, they can form a picture of the rings’ structures.
“Ring systems around giant planets also provide test beds for investigating fundamental physical properties and processes in our Solar System in general,” Dr. Jarmak said.
“These particles are thought to result from objects colliding and forming in a disk and building up larger particles.”
“Understanding how they form these ring systems could help us understand how planets form as well.”
The team’s work was published in the journal Icarus.
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S.G. Jarmak et al. 2022. Solar occultation observations of Saturn’s rings with Cassini UVIS. Icarus 388: 115237; doi: 10.1016/j.icarus.2022.115237
