DIX Planetary Science Seminar
Differential rotation and magnetic field generation are two natural outcomes in astrophysical and geophysical fluid systems. In the first part of this presentation, I will discuss differential rotation, also referred to as zonal flows, inside Jupiter. While Jupiter's visible cloud layer features east-west zonal flows ∼100 m/s, zonal flows in the dynamo region are significantly slower, ∼ cm/s or less. The vertical profile of the zonal flows and the underlying mechanism remain elusive. The latest Juno radio tracking measurements afforded the derivation of Jupiter's gravity field to beyond spherical harmonic degree ∼25. From the latest gravity solution, we reconstruct the deep zonal winds inside Jupiter without a priori assumptions about their latitudinal profile. The pattern of our reconstructed deep zonal winds strongly resembles that of the surface wind, in particular the northern off-equatorial jet (NOEJ) and the southern off-equatorial jet (SOEJ). Our analysis supports the physical picture in which the pattern of the surface zonal winds extends into Jupiter's interior significantly deeper than the water cloud layer.
The second part of this presentation concerns planet Mercury, the only terrestrial planet other than the Earth that harbors a planetary-scale magnetic field. Three defining features of Mercury's magnetic field are 1) its relatively weak strength (~1% of the Earth's surface magnetic field), 2) its strong north-south asymmetry, and 3) its axial dominance. There remain significant uncertainties in our understanding of the core properties of Mercury (e.g., the composition, the existence and extent of the iron snow zones, and the electrical conductivity), which directly impact our inference of the dynamo process inside Mercury. Here I will summarize a recent numerical dynamo survey which explores the double iron-snow regime inside Mercury's core. Our survey indicates that the lower iron snow zone, if exists, would suppress the axial north-south symmetry breaking in Mercury's observable magnetic field.
I will conclude this presentation with an outlook for upcoming observations and a summary of key open questions concerning differential rotation and magnetic field generation inside planets.