Data from the Cassini spacecraft show that Saturn’s moons work together to keep Saturn’s A ring intact.
Saturn and its moons [Image by NASA/JPL/David Sea]
Saturn’s rings aren’t actually solid, though they may seem that way. They’re made of tiny particles that are, in turn, made of water ice and a bit of rock. The A ring, in particular, is the outermost of the giant planet’s larger, brighter rings. As such, it is far enough away from Saturn that the planet’s gravity won’t be able to keep it intact on its own. Without the moons shepherding the particles of the ring, said particles would have drifted off to space until the ring completely disappears.
Janus above, Prometheus below [Image by NASA/JPL/Space Science Institute]
It was previously thought that a single Saturnine moon, Janus, was the only one herding the A ring’s particles into place. However, information from Cassini’s explorations of Saturn has shown that corralling the A ring’s particles is in fact a team effort, and six other rings are pulling their weight.
In addition to Janus, Saturn’s smaller moons Prometheus, Pandora, Pan, Epimetheus, and Atlas all do their part in keeping the A ring as manicured as possible. Another moon similar in size to Enceladus, Mimas, also lends a hand. Mimas is quite the industrious moon, seeing as it’s also the one keeping the B ring in check.
So how do these moons manage to keep tiny particles of ice and rock from drifting off into space?
When researchers reassessed the influence Janus has over the integrity of the A ring, they realized that they’ve been giving the Saturnine moon more credit than it deserved. Apparently, Janus is not massive enough to be the only one keeping the A ring particles where they should be. Thus, the researchers used Cassini’s data to create models of the planet’s rings and moons. The study suggested that a total of seven rings, instead of just one, have been working together to keep the A ring together.
Density waves created by the moons create the grooves in the rings. [Image by Cassini Imaging Team, SSI, JPL, ESA, NASA]
According to the findings, each of the seven moons provide “gravitational tugs” that create density waves. These density waves make it so that thicker ring material bunches up in specific locations within the ring itself. Those bunches take just enough angular momentum from the ring particles so Janus can hold the outer edge of the A ring.
Spacecraft Cassini crashed into Saturn in a planned death dive on September 15. However, it left mountains of data behind--data that scientists are steadily making more sense of. There are likely to be thousands more similar discoveries as researchers make their way through the data from the spacecraft.
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