Diagram of two Cassini spacecraft orbit trajectories during the “Grand Finale”
The left panel shows two Cassini spacecraft “Grand Finale” orbit trajectories cutting between the planet’s upper atmosphere (light orange region) and the ring regions (blue shaded regions, and their magnetic mapping to the planet). The right panel is a close-up of the space inside of the D ring, with arrows showing the newly identified current system flow. Credit: Hunt et al. [2019], Figure 1
Source: Journal of Geophysical Research: Space Physics

At the end of its mission life, the orbit of the Cassini spacecraft was positioned to move ever closer to the planet, in what are known as the Grand Finale orbits. Nearly two dozen times, it squeezed between the innermost ring and the planet, continuing to make observations until its very last moments.

Using data from these orbits, Hunt et al. [2019] reveal a previously undetected electric current system deep in Saturn’s rings. They also construct a reasonable hypothesis for how it is connected to the planet’s upper atmosphere.  The “closure currents” in the ionosphere are comparable in size those in the auroral zone, which close field-aligned currents from the outer reaches of Saturn’s space environment. That is, this is substantial current system, but it is so close to the planet that it went undetected until these final orbits of the Cassini mission that sent the spacecraft inside the planetary rings.

Citation: Hunt, G. J., Cowley, S. W. H., Provan, G., Cao, H., Bunce, E. J., Dougherty, M. K., & Southwood, D. J. [2019]. Currents associated with Saturn’s intra‐D ring azimuthal field perturbations. Journal of Geophysical Research: Space Physics, 124. https://doi.org/10.1029/2019JA026588

—Mike Liemohn, Editor-in-Chief, JGR: Space Physics

Text © 2019. The authors. CC BY-NC-ND 3.0
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