Ethylene Emission in the Aftermath of Saturn’s 2010 Northern Storm

The massive eruption at 40N (planetographic latitude) in December 2010 has produced significant and long-lived changes in temperature and species abundances in Saturn’s northern hemisphere (Fletcher et al. 2011). The northern storm region has been observed on many occasions between January 2011 and June of 2012 by Cassini’s Composite Infrared Spectrometer (CIRS). In this time period, temperatures in regions referred to as “beacons” (warm regions in the stratosphere at certain longitudes in the storm latitude) became significantly warmer than pre-storm values of 140K. A significant finding in the beacon region has been ethylene emission; a molecule that has been challenging to detect on Saturn but is an important species in Saturn’s photochemistry. The derived ethylene profile from the CIRS data gives a C2H4 mole fraction of 5.9 ± 4.5x10-7 at 0.5 mbar. Ground-based observations were performed using the high-resolution spectrometer Celeste to study ethylene’s spectral signatures at higher spectral resolution than available with CIRS. Analysis of the May 2011 Celeste data finds a C2H4 mole fraction of 2.7 ± 0.45x10-6 at 0.1 mbar. The ethylene abundances derived from CIRS and Celeste observations are two orders of magnitude higher than predicted by photochemical models, indicating that perhaps another production mechanism is required or a loss mechanism is being inhibited. To investigate the source of ethylene in the beacon region the temporal evolution of this molecule will be presented based on data collected by CIRS, between January 2011 and June 2012, together with ground-based Celeste observations from the McMath-Pierce Telescope (May 2011), the United Kingdom Infrared Telescope (July 2011), and the NASA Infrared Telescope Facility (April 2012). References: Fletcher, L. N. et al., 2011. Thermal Structure and Dynamics of Saturn’s Northern Springtime Disturbance. Science 332, 1413-1417.