Detection of visible lightning on Saturn

Abstract

Until now, evidence for lightning on Saturn has been indirect - through radio emissions and cloud morphology. Here we report the first visible detection of lightning, on the night side on August 17, 2009 at -36.4° ± 0.1° planetocentric latitude and 10.6° ± 0.9° west longitude. No other locations produced lightning detectable by either imaging or radio. The lightning images are consistent with a single cloud flashing once per minute. The visible energy of a single flash is comparable to that on Earth and Jupiter, and ranges up to 1.7 × 10⁹ Joules. The diameter of the lightning flashes is ∼200 km, which suggests the lightning is 125-250 km below cloud tops. This depth is above the base of the liquid H₂O-NH₃ cloud and may be either in the NH₄SH cloud or in the H₂O ice cloud. Saturn's lower internal heat transport and likely 5-10 fold enrichment of water largely explain the lower occurrence rate of moist convection on Saturn relative to Jupiter.