Polar Disturbance Surrounding a Long Living Cyclone in Saturn’s Atmosphere
Wednesday, 16 December 2015: 08:45
2007 (Moscone West)
In 2014 and 2015 a large ‘dark spot’ about 6,000 km in length and located at planetocentric latitude +58.5º (+63º N planetographic) was tracked on the best ground-based amateur images of Saturn, revealing a long-lived feature, an uncommon phenomenon in Saturn’s atmosphere. Images captured by the Imaging Science Subsystem (ISS) onboard Cassini spacecraft showed the feature as a very contrasted dark spot in the MT3 filter, and barely visible in the deep sounding filters CB2 and CB3. On mid-May 2015 ground-based observations obtained by amateur astronomers operating small telescopes started to show a disturbance around this dark spot. Following the onset of this disturbance the drift of the dark spot remained unaltered and equal to the motion it had previously, but the disturbance evolved zonally in a complex manner, giving hints of a kind of large scale phenomena in Saturn’s atmosphere of an unprecedented type. Unfortunately the orbital path of the Cassini spacecraft was not appropriate to see details of the disturbance at that time. Images by the Hubble Space Telescope (HST) WFC3 instrument obtained in director’s time (DDT) allow us to describe the detailed dynamics of the disturbance, while the study of its long-term evolution is possible thanks to the efforts of the community of amateur astronomers. In this work we analyse the dynamics of the region before the start of the disturbance and the dynamics and evolution of the disturbance after its onset.