New findings have been discovered on five tiny moons located in and near Saturn's rings. The nearest NASA spacecraft Cassini aircraft show that the surfaces of these unusual moons are covered with material from the rings of the planet – and from icy particles hurled from Saturn's larger moon, Enceladus. The work paints a picture of the competing processes that shape these mini-moons.
"The daring, narrow passers-by of these strange little moons let us take a look at their interaction with Saturn's rings," said Bonnie Buratti of the Jet Propulsion Laboratory of NASA Pasadena, California. Buratti led a team of 35 co-authors who published their work on March 28 in the journal Science. "We see more evidence of how extremely active and dynamic the Saturn-Ring-Moon system is."
The new research, Out of six data collected by Cassini's instruments before his mission ended in 201
Scientists also found that the lunar surfaces are highly porous. This further confirms that they were formed in several stages as the ring material settled on denser cores, possibly remnants of a larger object that broke apart. The porosity also helps in explaining its shape: they are not spherical, but blobed and ravioli-like, with material around their equators.
"We found that these moons scoop up ice and dust particles from the rings to form small skirts around their equators," Buratti said. "A denser body would be more spherical because gravity would pull in the material."
"This process may be carried out in the rings and the largest ring particles also form ring material around them, with detailed views of tiny ring moons telling us more about the behavior of the ring particles themselves," said Linda Spilker, scientist at the Cassini Project. also at JPL.
Of the satellites studied, the surfaces were those of Saturn-Daphnis and are most altered by ring materials. The surfaces of the moons Atlas, Prometheus and Pandora further away from Saturn also have ring material – but they are also covered with the bright ice particles and the water vapor of the Enceladus-spraying cloud. (A broad outer ring of Saturn, known as an E-ring, is formed by the icy material that emerges from Enceladus' cloud.)
The key piece of the puzzle was a record from the Visible and Infrared mapping Spectrometers from Cassini (VIMS). which have collected visible light to the human eye as well as longer wavelength infrared light. It was the first time that Cassini was close enough to make a spectral map of the surface of the innermost moon pan. By analyzing the spectra, VIMS was able to learn the composition of the materials on all five moons.
VIMS recognized that the ring moons closest to Saturn appear most reddish, similar to the color of the main rings. Scientists do not yet know the exact composition of the material that appears red, but they believe that it is probably a mixture of organic matter and iron.
The moons outside the main rings, on the other hand, appear rather blue the light of Enceladus' icy clouds.
Six overboard fly-bys of ring moons between December 2016 and April 2017 included all Cassini optical remote sensing instruments that study the electromagnetic spectrum. They worked alongside the instruments that studied dust, plasma, and magnetic fields, and how these elements interact with the moons.
There remain questions, including the question of what caused the moons. Scientists will use the new data to model scenarios, and they could transfer the findings to small moons around other planets and possibly even asteroids.
"Do the moons of the ice giant planets Uranus and Neptune interact with their thinner rings to form features similar to those on Saturn's ring moons?" Buratti asked. "These are questions to be answered by future missions."