Gregory J. Hunt

PS Planetary and Solar System Sciences

The 2022 Division Outstanding Early Career Scientist Award is awarded to Gregory J. Hunt for outstanding research on the magnetic signatures associated with large-scale current systems within Saturn’s magnetosphere, with special emphasis on aurorae and periodicities.

Gregory Hunt is nominated for an EGU Arne Richter Award for Outstanding Early Career Scientists in recognition of his exceptional achievements in elucidating the nature of magnetosphere-ionosphere coupling currents at Saturn through detailed analysis of magnetic field data from the Cassini orbital space mission. Electric currents flowing along high-latitude planetary field lines connect currents flowing in the planetary ionosphere with those flowing in the magnetosphere, these current circuits being the means by which momentum is communicated between these regions. Study of field-aligned currents is thus of fundamental importance to the physics of planetary plasma environments. During the course of his PhD studies at Leicester (2013/16), Hunt was the first to undertake detailed analyses of the magnetic perturbations in high-latitude Cassini data from which field-aligned currents can be quantified, in particular inventing a methodology which allows the disentangling of the quasi-steady currents associated with the maintenance of partial rotation of the magnetospheric plasma with the planet, from the rotating systems of bipolar currents associated with Saturn’s unique northern and southern ‘planetary period oscillations’ (PPOs). Although Saturn’s internally-generated magnetic field is axially symmetric to measurement accuracy, oscillations near the planetary rotation period are nevertheless ubiquitous in field and plasma data throughout the magnetosphere. Hunt’s work proved that these oscillations are driven outward from the two polar atmospheres into the magnetosphere, in general with slightly different seasonally-dependent rotation periods in the range ~10.6-10.8 h. Both northern and southern oscillations were found to be present together in the auroral and inner regions, but only one oscillation characteristic of that hemisphere was found to be present in each of the polar regions. After the award of his PhD, Gregory Hunt moved to the space magnetometer group at Imperial College London (2016-present) where he has played a major role in the analysis of the unique magnetic field data acquired on the final set of Cassini proximal orbits in 2017, when the spacecraft passed at periapsis through the gap between the inner planetary D ring and the upper layers of Saturn’s atmosphere. His work on behalf of the Cassini magnetometer team has generously enabled a wide range of co-authored collaborative studies with international colleagues, including work on ring interactions and new high-order models of the planetary magnetic field. Hunt has himself led studies of the auroral currents observed on these passes, finding first evidence of variations associated with solar wind-modulated magnetospheric dynamics. He has also led work quantifying the current densities of the newly discovered interhemispheric field-aligned currents flowing on near-equatorial field lines inside of Saturn’s inner D ring, believed to be driven by near-equatorial north-south upper atmospheric wind shears. Overall, much of what we know about the coupling currents in Saturn’s outer plasma environment derives from the studies led by Gregory Hunt, such that his work will undoubtedly remain as standard references in the field for many decades to come. He is thus well deserving of recognition through an EGU Arne Richter Award for Outstanding Early Career Scientists.