As the Cassini spacecraft plunged to its doom it reported a sharp drop off in Saturn’s hectic winds with depth. This initially puzzling observation has now been explained as a consequence of the planet’s interior being viscous, which in turn is a consequence of the warping of its magnetic field.
Saturn is a gas giant, composed of hydrogen and helium rather than solid materials like the Solar System's rocky inner planets. Although it lacks the distinct coloring of Jupiter, the outer parts of the planet are composed of jet streams, circling the planet at speeds of up to 1,800 kilometers (1,100 miles) per hour.
After 13 wonderful years of studying Saturn, its moons and rings, Cassini did a final dive into the planet as its last act of service to humanity, sending back a wealth of data before it was crushed by the intense pressure. “The measurements revealed that these jet streams continue about 8,500 kilometers inside Saturn, which is roughly 15 percent of the distance towards the planet’s center,” said Dr Navid Constantinou of the Australian National University in a statement.
Beneath this the movement stops. Planetary scientists have sought to explain this unexpected finding, and Constantinou has published what he thinks is the answer in Physical Review Fluids.
“Deep into Saturn, where the pressure is high, the gas becomes a liquid that conducts electricity and is more strongly influenced by the planet’s magnetic field,” Constantinou said. “Beyond certain depths the pressure is so high the electrons break loose from the hydrogen molecules and are allowed to move freely," he added to IFLScience. "Electrons moving freely create currents. Beyond those depths we say that ‘the fluid becomes conducting’, i.e., it can carry electric currents and, consequently, can be affected by magnetic fields.”
According to Constantinou, the jet streams bend the magnetic field lines, and the distorted fields make Saturn more viscous at depth, in other words, more like slowly flowing honey than swift-moving water. Constantinou says the estimates are still imprecise, but deep inside Saturn, the viscosity is millions, probably hundreds of millions, of times greater than anything you'd put on pancakes.
“The mysteries of what goes on inside Saturn and the other gas giants in our Solar System are now slowly starting to be unveiled,” Constantinou said. Although he does not anticipate any direct practical outcomes from the findings, Constantinou thinks they will improve our understanding of the interiors of other gas giants, not just those within the Solar System, but the many we are detecting around other stars.