ENA periodicities at Saturn

The Magnetospheric Imaging Instrument (MIMI) on the Cassini spacecraft has observed energetic neutral atoms (ENA) at Saturn for three years from 2004 to 2007. The 20-50 keV hydrogen and 64-144 keV oxygen neutrals were examined for periodic behavior by projecting their images onto a plane perpendicular to Saturn's equatorial plane and summing the emissions along the vertical. The resulting strip'' images were then subjected to a Lomb periodogram analyses for the period between mid-2004 to mid-2007. The hydrogens display erratic periods in the 8-13 hour range, while the oxygens exhibit a very strong, repeatable period of 10.8 +/- 0.2 hours, which is close to the nominal period of Saturn kilometric radiation as well as the period of energetic particles in Saturn's outer magnetosphere.