SM42B-08
Simulating Negative Pickup Ions and Ion Cyclotron Wave Generation at Europa
Thursday, 17 December 2015: 12:05
2009 (Moscone West)
Ravindra T Desai1, Misa Cowee2, S Peter Gary2, Hanying Wei3, Andrew J Coates4 and Dhiren O Kataria5, (1)Mullard Space Science Laboratory, UCL, Dorking, RH5, United Kingdom, (2)Los Alamos National Laboratory, Los Alamos, NM, United States, (3)University of California Los Angeles, Los Angeles, CA, United States, (4)University College London, Centre for Planetary Sciences (at UCL/Birkbeck), London, United Kingdom, (5)Mullard Space Science Laboratory, UCL, Dorking, United Kingdom
Abstract:
The mass loading of space environments through the ionisation of planetary atmospheres is a fundamental process governing the plasma interactions and long term evolution of celestial bodies across the solar system. Regions containing significant pickup ion populations have been observed to exhibit a rich variety of electromagnetic plasma wave phenomena, the characteristics and properties of which can be used to infer the ion species present, their spatial and temporal distributions, and the global ionisation rates of the neutral material. In this study we present hybrid (kinetic ion, massless fluid electron) simulations of ion pickup and Ion Cyclotron (IC) waves observed in the Jovian magnetosphere and draw comparisons to sub-alfvénic pickup observed by Cassini in the Saturnian system, and also to supra-alfvénic pickup at planetary bodies immersed directly in the solar wind. At Jupiter, Europa has been identified as the secondary mass loader in the magnetosphere, orbiting within a neutral gas torus at ~9.38 Rj. Near Europa, Galileo magnetometer observations displayed bursty IC wave characteristics at the gyrofrequency of a number of species including SO2, K, Cl, O2, and Na, suggesting a complex mass loading environment. A particular deduction from the dataset was the presence of both positively and negatively charged pickup ions, inferred from the left and right hand polarisations of the transverse waves. Using hybrid simulations for both positively and negatively charged Cl pickup ions we are able to self-consistently reproduce the growth of both right and left hand near-circularly polarised waves in agreement with linear theory and, using the observed wave amplitudes, estimate Cl pickup ion densities at Europa.