ENA periodicities at Saturn

Abstract

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.