Saturn’s moons are much younger than previously thought, according to freshly harvested data from NASA’s Cassini mission of the ringed planet’s bulging core and twisting gravitational forces.
Scientists measured Saturn’s Love number – the rigidity of a planet – for the first time and confirmed Saturnian moons move away from the planet at a faster rate than expected. “All of these Cassini mission measurements are changing our view of the Saturnian system, as it turns our old theories upside down. It takes one good spacecraft to tell us how wrong we were in the past,” said Radwan Tajeddine, research associate at Cornell University in the US.
Using photographic images taken from century-old glass negatives and Cassini spacecraft observations, the group measured the Love number. While Saturn is mostly a gigantic shroud of liquid hydrogen and liquid helium, it contains a rocky core – about 18 times the size of Earth, which responds to tidal forces from all of Saturn’s major moons by bulging.
The forces of the bulging core, in turn, push the moons slightly away. “Those two parameters – the Love number and dissipation factor – are difficult to separate,” said Tajeddine, also a member of the European-based Encelade scientific team that pored over the Cassini data.
The team detected and examined the orbits of four tiny moons associated with the larger moons Tethys (Telesto and Calypso) and Dione (Helene and Polydeuces). While these tiny moons do not affect the tidal forces on Saturn, their orbits are disturbed by Saturn’s core tidal bulges.
“By monitoring these disturbances, we managed to obtain the first measurement of Saturn’s Love number and distinguish it from the planet’s dissipation factor,” Tajeddine said. “The moons are migrating away much faster than expected,” said Tajeddine.
Tajeddine explained that if Saturn moons actually formed 4.5 billion years ago, their current distances from the home planet should be greater. The new research suggests that the moons are younger than 4.5 billion years, favouring a theory that the moons formed from Saturn’s rings.
The team also found that Saturn moon Rhea is moving away 10 times faster than the other moons, which is the first evidence that a planet’s dissipation factor can vary with its distance in relation to the moon.
After 13 years of cruising around Saturn, to explore its rings and moons, NASA will programme Cassini’s grand finale – a flight through the planet’s rings and a dive into its atmosphere – for September 2017.
“What we believe about Saturn’s moons history might still change in the coming years with the finale of the Cassini mission,” said Valery Lainey of the Paris Observatory.
The study was published in the astronomy journal Icarus.