Scientists compile Cassini’s unique observations of Saturn’s rings

Southwest Research Institute scientists have compiled 41 solar occultation observations of Saturn’s rings from the Cassini mission. The compilation recently published in the magazine Icaruswill inform future studies of the particle size distribution and composition of Saturn’s rings, key elements in understanding their formation and evolution.

“For nearly two decades, NASA’s Cassini spacecraft shared the wonders of Saturn and its family of icy moons and distinctive rings, but we still don’t definitively know the ring system’s origins,” said Dr. Stephanie Jarmak, a researcher in the SwRI Space Science Division. “Evidence suggests the rings are relatively young and could have formed from the destruction of an icy satellite or a comet. However, to support an origin theory, we need to have a good idea of ​​the size of the particles that make up the rings. “

Cassini’s Ultraviolet Imaging Spectrograph (UVIS) was uniquely sensitive to some of the smallest ring particles, particularly in the observations it made in the extreme ultraviolet.

To determine the size of the ring particles, UVIS observed them when the instrument was pointed at the Sun and looking through the rings in what is known as a solar eclipse. Ring particles partially blocked the light’s path, providing a direct measurement of optical depth, a key parameter in determining ring particle size and composition.

“Given the wavelength of light coming from the Sun, these observations gave us insight into the smallest particle sizes associated with Saturn’s rings,” Jarmak said. “UVIS can detect dust particles in the micron range, helping us to understand the origin, collision activity and destruction of the ring particles within the system.”

The compilation also addresses the variations in optical depth of occlusion observations, which can help determine particle size and composition. During an occlusion, light emitted by a background source such as the sun is absorbed and scattered by the particles in the light path. The amount of light blocked by ring particles provides a direct measurement of the optical depth of the ring.

Including optical depth is crucial to understanding the structure of the rings. The research measured optical depth as a function of viewing geometry, which relates to the viewing angles of the ring system relative to the Cassini spacecraft. Because the light passing through the rings changes at different angles, scientists can get a picture of the rings’ structure.

“Ring systems around giant planets also provide testbeds for studying fundamental physical properties and processes in our solar system in general,” Jarmak said. “These particles are thought to result from objects colliding and forming in a disk, building up larger particles. Understanding how these ring systems form could help us understand how planets form as well.”

The paper appears in Icarus.