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Although NASA's Cassini mission ended in 2017, science continues to flow from the data collected. In a series of articles in the newspaper Science, planetary researchers analyzed data from Cassini's orbits (December 2016 to April 2017) and its grand finale phase (April to September 2017). Among the main discoveries, there is the discovery that the rings of Saturn are relatively young, probably between 10 and 100 million years old.
NASA's Cassini probe orbiting Saturn. Image credit: NASA / JPL-Caltech.
"The rings of Saturn are an accessible example of the astrophysical disk processes and a delicate tracer of the dynamic processes and history of the Saturn system," said Cassini scientist Matt Tiscareno of the SETI Institute and his colleagues .
"During its grazing orbits and grand finale, Cassini came very close to the main rings of Saturn and obtained very high spatial resolution images, spectral scans and temperature readings."
Dr. Tiscareno's team analyzed these images and scans and discovered complex features sculpted by the gravitational interactions between Saturnian moons and annular particles.
The false-color image on the right shows the spectral mapping of Saturn's rings A, B and C, captured by the Cassini Visible and Infrared Mapping Spectrometer (VIMS). It displays an infrared view of dark circles rather than an image in visible light. The blue-green areas are the areas where the ice is the purest and / or the largest grain (mainly A and B rings), while the reddish color indicates increasing amounts of non-glossy material and / or smaller sizes (mainly C ring and Cassini Division). On the left, the same image is superimposed on a naturally colored Saturn mosaic taken by Cassini's Imaging Science Subsystem (ISS). Image credit: NASA / JPL-Caltech / Institute of Space Sciences / G. Ugarkovic / University of Arizona / CNRS / LPG-Nantes.
"On the outer edge of the main rings, a series of similar streaks generated by an impact in the F ring have the same length and the same orientation, which shows that they were probably caused by a group of Impacts that all hit the ring at the same time, "said the scientists.
This shows that the ring is formed by streams of material that revolve around Saturn itself rather than, for example, by cometary debris (moving around the Sun) that breaks in the rings.
"These new details of how moons carve rings in different ways open a window to the formation of the solar system, where discs also evolve under the influence of embedded masses," said Dr. Tiscareno.
This mosaic of enhanced color images shows Daphnis in the Keeler space on the sunny side of the rings. Daphnis is seen lifting three waves in the outer edge of the ditch. Image credit: NASA / JPL-Caltech / Institute for Space Science.
A team led by Dr. Bonnie Buratti of NASA's Jet Propulsion Laboratory analyzed Cassini's observations of the five small moons located in and around the rings of Saturn.
"The main ring system of Saturn is associated with a family of small moons," said the researchers.
"Pan and Daphnis orbit respectively in Encke Gap and Keeler Gap, while Pandora and Prometheus orbit just outside the F ring and Atlas, just outside of the ring A . "
"The Janus and Epimetheus moons are in widely spaced orbits that they exchange about every four years. these two objects can be collision fragments of a larger body. "
"Five close fly-bys of the Pan, Daphnis, Atlas, Pandora and Epimethea moons were made between December 2016 and April 2017 during the grazing orbits of the Cassini mission.
"Data on the morphology, structure, particle environment and composition of the moons were returned, as well as images in the ultraviolet and thermal infrared."
During the very tight overflights of Saturn's rings, Cassini inspected the mini-moons Pan and Daphnis in ring A; Atlas at the edge of the ring A; Pandora at the edge of the ring F; and Epimetheus, who is bathed in matter coming out of the moon, Enceladus. Image credit: NASA-JPL / Caltech.
They discovered that the optical properties of the moon's surfaces are determined by two competing processes: the contamination by a red material formed in the ring system of Saturn and the accumulation of glossy icy particles or water vapor from volcanic plumes from of the moon Enceladus.
"We found that these moons accumulate ice and dust particles in the rings to form small skirts around their equators," said Dr. Buratti.
"A denser body would be more ball-shaped because gravity would attract material to the interior."
During the grand finale, NASA's Cassini spacecraft passed between the inner edge of Saturn's D ring and the top of the clouds. This orbital configuration made it possible to unravel the small acceleration of the rings of the strong acceleration due to Saturn. Both forces pull the probe in opposite directions. Image credit: NASA / JPL-Caltech / Iess et al.
A research team led by Dr. Luciano Iess of Rome's Sapienza University measured the gravitational pull on Cassini, separating contributions from the planet and rings.
This allowed them to determine the inner structure of Saturn and the mass of its rings.
"The Cassini gravity field measured by Cassini involves a strong and deep differential rotation, up to a depth of about 5 600 miles (9000 km). This is different from Jupiter, where the winds are weaker (1,864 km), they said.
"Gravity measurements correspond to a mass of 15 to 18 Earth masses in the core of Saturn."
Scientists have discovered that the total mass of the rings is 1.54 * 1019 – about 0.41 times that of the Saturnine Moon Mimas.
"The low value of the ring mass suggests a scenario in which the current rings of Saturn are young, probably 10 to 100 million years old, to be consistent with their immaculate ice composition," they said. they said.
Models for a young ring system invoke the incidental capture and tidal disturbance of a comet or icy body of the outer solar system, suggesting that catastrophic events have continued to occur. produce in the solar system well after its formation there are 4.6 billion years. "
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Matthew S. Tiscareno et al. 2019. Remote sensing of the rings of Saturn during the Cassini orbits and grand finale. Science 364 (6445): water 1017; doi: 10.1126 / science.aau1017
B.J. Buratti et al. 2019. Close Saturn rings of Pan, Pan, Daphnis, Atlas, Pandora and Epimetheus by Cassini. Science 364 (6445): eaat2349; doi: 10.1126 / science.aat2349
L. Iess et al. 2019. Measurement and implications of the gravity field and the ring mass of Saturn. Science 364 (6445): eaat2965; doi: 10.1126 / science.aat2965
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