Cassini’s mission around the sixth planet from the Sun and its moons has so far uncovered a lot of new elements about Saturn that scientists have been trying to figure out for centuries. Almost five years after entering Saturn’s orbit, Cassini may have found the source of the planet’s G ring and its ring arc, in the shape of an embedded moonlet.
Saturn is generally known for its impressive system of rings, the largest in our Solar System. Almost 400 years after Galileo Galilei first spotted them through his telescope, and 350 years after Huygens first described them as disks surrounding Saturn, Cassini may have solved the enigma surrounding one of the planet’s outer rings.
The G ring, name in the order the rings have been discovered (D, C, B, A, F, G, E looking outward), is bright and narrow, only 250 kilometers wide, and is quite diffuse. Based on previous Cassini images, the ring was believed to have been produced by relatively large, icy particles, embedded within the arc, but it wasn’t until 2008 that the scientists imaged the moonlet. Since then, they have seen it on multiple occasions, the last of which was last month.
“Before Cassini, the G ring was the only dusty ring that was not clearly associated with a known moon, which made it odd,” said Matthew Hedman, Cassini imaging team associate at Cornell University in Ithaca, N.Y. “The discovery of this moonlet, together with other Cassini data, should help us make sense of this previously mysterious ring.”
The G ring is about 15000 km inside the orbit of Mimas, one of Saturn’s moons, and as scientists explained it, the moonlet’s orbit is being disturbed by Mimas, which is also responsible for keeping the arc together.
“The moon’s discovery and the disturbance of its trajectory by the neighboring moon Mimas highlight the close association between moons and rings that we see throughout the Saturn system,” said Carl Murray, Cassini imaging team member and professor at Queen Mary, University of London. “Hopefully, we will learn in the future more about how such arcs form and interact with their parent bodies.”
Speaking of rings, Cassini is also responsible for revealing for the first time what appeared to be a ring around Saturn’s second largest moon, Rhea. According to the data sent by the spacecraft after a 2005 flyby, Rhea is surrounded by a broad debris disk, made up of a multitude of particles, with a wide range of sizes, from small pebbles to boulders.
Cassini was once again in the spotlight last year, when scientists spoke of evidence pointing to the existence of an underground ocean on one of Saturn’s moons, Titan. The images that led scientists to such assumptions were taken with the help of Cassini’s radar observations on the moon’s rotation between 2004 and 2007.
With the help of Cassini, scientists are also conducting extensive research on the geyser-jets on Saturn’s sixth’s largest moon, Enceladus. Their presence indicates the existence of water not so far beneath the surface of the moon.
