Beneath Saturn's stormy exterior, conductive liquids appear to flow like honey
Gas giants like Saturn with their facade of swirling superstorms are brimming with mystery, but intrepid spacecraft like Cassini are beginning to unravel their secrets. The probe burned up like a meteor when it plunged into the planet’s atmosphere two years ago, but not before returning a wealth of information to researchers here on Earth. Scientists studying this data have now constructed a new picture of Saturn’s insides, describing jet streams that continue deep below the surface to meet a viscous liquid that “flows like honey.”
Much like its gassy sibling Jupiter, Saturn experiences ferocious winds, or jet streams, that circle the globe and give it a stripy appearance. Until recently, how deep below the exterior these jet streams continue has been something of an unknown.
In Jupiter’s case, last year the Juno probe studied that planet’s gravitational field to reveal they continue some 3,000 km (1,900 mi) below the surface. Coincidentally, this also happens to be point that the planet’s magnetic field appears to start having a strong effect on the liquids making up its core. This interface between the jet streams and the magnetically influenced gases led some scientists to hypothesize that the magnetic effect could be very the reason the jet streams end where they do.
Analysis of Cassini data earlier in the year unearthed some parallels, finding that Saturn’s jet streams continue to depths of 8,500 km (5,280 mi) before a similar effect suddenly takes hold. Dr Navid Constantinou from Australian National University’s Research School of Earth Sciences has been looking into the reasons why.
“This is the depth that magnetic fields start have a strong influence on the fluid in Saturn’s interior; similarly in Jupiter as well,” he explains to New Atlas. “So there exists the hypothesis that magnetic fields have something to do with why the jet streams stop at those depths, but nobody really knows the mechanisms behind how magnetic fields influence the jet streams.”
In a new study, Constantinou, together with co-author Jeffrey Parker from Lawrence Livermore National Laboratory, put forward a theory that explains why magnetic fields might put a sudden stop to jet streams deep inside these gassy giants. The scientists built theoretical predictions based on simple physical arguments and found that the jet streams caused distortions of magnetic field lines, which in turn make the planet’s internal fluids highly viscous. They then explored these predictions further through simulations of magneto-fluid dynamics.
“The agreement of our predictions with the numerical simulations was astonishing, and this gave us faith that our theoretical argument is on the right track,” Constantinou tells us.
The scientists believe that at these depths, which for Saturn is around 15 percent of the distance from the cloud tops to its center, high pressures convert the liquids into an electrically conductive liquid that can be influenced by the planet’s magnetic fields. As the jet streams bend or distort the planet’s magnetic field, those distortions cause the liquids to become more viscous, “like honey,” which could be why the jet streams come to a stop at 8,500 km.
Constantinou describes this as probably the “first theoretical prediction that holds for turbulent magnetohydrodynamic flows,” as they are known, but notes the need for further study. This could come through more detailed simulations and comparisons between data from Jupiter and Saturn, or from future spacecraft missions that could more closely measure flow and magnetic field structures hidden within gas giants.
“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 says.
The research has been published in the journal Physical Review Fluids.
Source: Australian National University