|Title:||Testing the Onset of a Polar Vortex at Saturn's Northern Summer Solstice by Mapping Stratospheric Temperature and Hydrocarbons|
|Co-I(s):|| Thomas Greathouse, Thierry Fouchet, Leigh Fletcher, Aymeric Spiga, Sandrine Guerlet, James Sinclair|
We propose high spatial- and spectral-resolution observations of Saturn’s north polar region that can only be made using the TEXES instrument at Gemini North to examine the evolution of a very striking polar phenomenon that is unmatched elsewhere in the solar system. It is the result of strong insolation variations over the course of its 29.5-year orbit and its axial tilt of 26.7°. A southern counterpart was observed at southern summer (2004-2006): a warm polar vortex that extended to 75°S, which also contained significant enhancements in acetylene and ethane over regions closer to the equator. Many questions remain regarding its vertical structure and its dynamical versus radiative origin. With Saturn’s approach to the summer solstice (May 2017), the northern pole is now completely visible to ground-based observers for the first time since 1987. This represents a unique opportunity to study the onset of a northern counterpart of the warm southern polar hood. We propose to take advantage of the unique combination of the high spectral resolution of the TEXES thermal infrared spectrometer and the high diffraction-limited spatial resolution provided by Gemini in order to resolve the latitudinal and vertical fields of the temperature, C2H2 and C2H6 over the entire summer hemisphere centered at the north pole. These observations will be highly complementary to the existing observations from the Cassini mission that only probed the 1-5 mbar level, but tracked changes from 2004 to the present. This will be the last opportunity to make such a comparison before the end of the Cassini mission in September, 2017. By deriving the 2-D structure of the temperature and composition, and by comparing the results with existing radiative and photochemical models, we aim to bring new constraints on how Saturn's stratospheric chemistry and dynamics responds to extreme seasonal changes.