LANCASTER, England, January 15, 2020 – Nearing the completion of its 13-year mission, which ended in September 2017, the Cassini spacecraft completed a series of orbits that brought it closer to Saturn than ever before. Flying over the planet’s polar regions at low altitude, Cassini’s ultraviolet camera was able to observe Saturn’s auroras with unprecedented resolution. Scientists from Lancaster University analyzed the high-resolution images showing the fine-scale structure of the aurora borealis.
Images from the final leg of Cassini’s journey show for the first time the detailed structure of the main auroral arc, which varies between a smooth and wavy shape, likely depending on how quiet or disturbed the plasma is near Saturn. The images show several parallel arcs near dusk, the origins of which are not easily explained with current understanding of how Saturn’s auroras are driven. Outer emission, although variable in brightness, is still present, and scientists believe it could be driven by hot electrons from the ring current.
Composite of a true-color image of Saturn, observed by Cassini in 2016, overlaid with a false-color representation of the ultraviolet aurora in the northern hemisphere observed on August 20, 2017. Courtesy of NASA/ JPL-Caltech/Space Science Institute/UN. Bader (University of Lancaster).
Lancaster University researcher Alexander Bader said: “This latest set of close-up images gives us unique and highly detailed views of small-scale structures that could not be discerned in previous observations. from Cassini or the Hubble Space Telescope. We have some ideas about what their origin might be, but there is still a lot of analysis to be done.
Saturn’s auroras, located in the planet’s polar regions, are known to be very dynamic, often pulsating and flashing as different dynamic processes occur in the planet’s plasma environment.
Even though Cassini’s mission is over, the data it provided will continue to help researchers understand how giant planetary auroras work, especially in combination with Juno observations of Jupiter’s magnetosphere. This final set of images will be the only high-resolution data for the foreseeable future, the researchers said, and will therefore provide an important baseline for future auroral research on Saturn.
The research has been published in Geophysical Research Letters (www.doi.org/10.1029/2019GL085800) and in Space Physics JGR (www.doi.org/10.1029/2019JA027403).