Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
1766921 | Advances in Space Research | 2009 | 11 Pages |
Abstract
The Magnetospheric Imaging Instrument (MIMI) on the Cassini spacecraft has observed energetic neutral atoms (ENA) and charged particles at Saturn from mid-2004 to the present. The particles often but not always reveal striking periodic behavior that seems to depend on the type of particle and spacecraft location. When subjected to a Lomb periodogram analysis, energetic electrons (>150Â keV) exhibited strong frequency peaks near 10.80Â h (the nominal or “base” period of Saturn kilometric radiation) during 2006-2008, but essentially no periodicity during 2005. The electron periodograms also show pronounced “double” frequency peaks in 2007 and 2008. Energetic protons (3-26Â keV) show strong peaks near the same period for 2005-2007, but none for 2008. Oxygen ions at the same energies display strong peaks for 2005 and 2006, but not for 2007 and 2008. By projecting the ENA images onto Saturn's equatorial plane or onto a plane perpendicular to the equatorial plane and then summing the data in the appropriate dimension, “strip” images can be constructed from which a time history can be derived. These time histories of ENA emissions are also subjected to a Lomb periodogram analyses. The energetic hydrogen neutrals (20-50Â keV) exhibited periodic behavior only during 2007, while energetic oxygen neutrals (64-144Â keV) displayed a strong SKR-like period in 2005 and 2006 but not for 2007 or 2008. Some of this behavior may be due to changing spacecraft aspect relative to the ENA emissions, and some of it may be real. This periodic behavior may be consistent with a rotating anomaly that “flashes” brightly in the midnight-to-dawn sector once per 10.8Â h, with the flash parameters depending on particle species and energy.
Related Topics
Physical Sciences and Engineering
Earth and Planetary Sciences
Space and Planetary Science
Authors
James F. Carbary, Stamatios M. Krimigis, Donald G. Mitchell, C. Paranicas, P. Brandt,