Research brief: How magnetic fields can make water behave like honey

Picture: This enhanced color view of Jupiter’s south pole was created by citizen scientist Gabriel Fiset using data from the JunoCam instrument on NASA’s Juno spacecraft.  Credit: NASA/JPL-Caltech/SwRI/MSSS/Gabriel Fiset

Turning on a magnetic field may make fluids that conduct electricity behave more like honey than like water.  Our theoretical study shows that the interplay of fluid motion with a magnetic field can, in effect, cause the fluid to be more viscous.

This discovery may help explain a mystery of Jupiter’s zonal winds, the alternating east-west jet streams, seen in photographs as colourful stripes.  NASA’s Juno mission to Jupiter revealed that the zonal winds descend to a depth of about 3,000 km — about 4% of Jupiter’s radius.  But why do they stop there?  Scientists have hypothesized that magnetic fields are responsible, but the physical mechanism has yet to be explained.

This study may help elucidate how magnetic fields do the job.  Deeper into the planet, where the pressure is higher, the atmosphere becomes more conducting and is more strongly influenced by the planetary magnetic field.  The magnetically enhanced viscosity could be strong enough to be the culprit that terminates the winds at depths below 3,000 km.  Although further studies would be necessary to confirm if this effect is truly responsible, this work provides a direction for additional research.

  • Paper: Parker, J. B. and Constantinou, N. C. (2019). Magnetic eddy viscosity of mean shear flows in two-dimensional magnetohydrodynamics. Phys. Rev. Fluids, 4, 083701. https://doi.org/10.1029/2019MS001769

By Alvin Stone

Alvin worked as an editor with Fairfax Community News and then News Local for over a decade before moving across to media communications. As a media communicator he has worked for WWF-Australia and most recently Primary Communication, a boutique agency specialising in corporate clients in the energy, transport, IT and not-for-profit sectors.