The ion composition of Saturn's magnetosphere
Abstract
We present magnetospheric ion composition results obtained from the Cassini Plasma Spectrometer (CAPS) time-of-flight instrument for orbits over a two year period in which Cassini was almost entirely in the dawn magnetosphere. Water group ions (O+ , OH+ , H2 O+ , H3 O+ ; or collectively, W+ ) dominate over H+ in the inner magnetosphere to approximately L = 25. W+ ions are seen sporadically out to L = 36. Within the water group, O+ dominates at all distances, H3 O+ is second to O+ for L < 5, H2 O+ is second from L = 5 to L = 7, and OH+ is comparable to O+ for L > 7. The density of H3 O+ peaks at L = 4 and drops off rapidly, becoming undetectable beyond L = 15. We also present ion population profiles as a function of distance above the equatorial plane. As expected, H+ has the longest scale height, Hz ∼ 2 RS at L = 4, whereas for W+ ions Hz ∼ 1 RS at this distance. The exception is H3 O+ , for which Hz ∼ 0.5 RS. Furthermore, the scale height tends to increase slowly with distance. Finally, we discuss ion energetics. The W+ plasma has both a core and a high energy tail; characteristics of each component have a separate dynamical history and vary as a function of radial distance. The ratio of number densities for the tail to the core is seen to have a broad peak between 10 < L < 20, indicating a source mechanism in this location, possibly the ring current.
- Publication:
-
37th COSPAR Scientific Assembly
- Pub Date:
- 2008
- Bibcode:
- 2008cosp...37.2593R