The Discovery of Rhea as a Source of Nitrogen Ions
Abstract
The Cassini plasma spectrometer (CAPS) instrument made measurements of the plasma envi-ronment near Rhea when Cassini passed through the moon's wake on November 26, 2005 at a distance of 500 km, and again on August 30, 2007, at a distance of 5000 km. During both en-counters, the CAPS ion mass spectrometer (CAPS/IMS) detected an enhancement of nitrogen ions (N+ ) by a factor of two relative to the ambient environment. Compared to water group ions (O+ , OH+ , H2 O+ , H3 O+ ), this amounted to a fractional increase from 10% to 20% of the water group content. There has already been a suggestion that Rhea possesses a dust halo (Jones, et al., Science 2008) and that it is a source of O2 + (Martens et al., GRL, 2008). Our results provide further evidence that Rhea is a source of plasma for Saturn's magnetosphere. To explore the degree to which Rhea may have an active surface, modeling of the nitrogen source rate is currently under way. We will present our current results as well as composition results from the upcoming Rhea encounter on March 2, 2010, when Cassini passes within 100 km of the moon.
- Publication:
-
38th COSPAR Scientific Assembly
- Pub Date:
- 2010
- Bibcode:
- 2010cosp...38..576R