The source of the H cloud shown in Cassini UVIS H Ly-a map in 2005
Abstract
The origin of the broad hydrogen cloud in Saturn's magnetosphere observed by Voyager and Cassini has been debated ever since it was discovered by Broadfoot et al. (1981). Proposed sources included Titan's H torus shaped by solar radiation pressure (Smyth and Marconi, 1993; Ip, 1996) and hydrogen atoms flowing outward from Saturn (Shemansky and Hall, 1992; Shemansky et al., 2009). From the H Ly-alpha intensity map observed by Cassini UVIS, Shemansky et al. (2009) suggested that a peaked brightness on Saturn's disk and an enhancement below the ring plane were evidence of H outflow from Saturn. The Saturnian magnetosphere is also immersed in a neutral cloud (H2O, O2 and H2) and their dissociate products, which originate from several sources, including the Enceladus plumes, the rings, the inner icy satellites and Titan's H2 torus (e.g., Tseng et al., 2011). Tseng et al. (2013) have carried out a global investigation of the atomic hydrogen cloud taking into account all possible sources above. Our simulations showed that H directly escaping from Titan is a major contribution in the outer magnetosphere. For the H cloud in the inner magnetosphere (as shown in the Cassini UVIS H Ly-a map in 2005 presented in Melin et al., 2009), we found that the H from photodissociation of the H2 cloud around the main rings has a similar morphology to that indicated by the observations, but with a smaller intensity. This work will be focused on further exploring the H from 1) the H2 cloud around main rings and 2) directly from the rings. The source mechanism (i.e., H+ neutralized by the rings) and the interaction of H with the ring particles (i.e., ring absorption, energy reduction due to re-impact on the rings, and possibly preferential re-emission below the ring plane due to sunlight) will be investigated over a large parametric space. In addition, a resonant line radiative transfer model will be used to convert the simulated H column density into H Ly-a intensity, taking into account the nearly optically thick H cloud and opacity of the rings.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2013
- Bibcode:
- 2013AGUFM.P43A2004T
- Keywords:
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- 0343 ATMOSPHERIC COMPOSITION AND STRUCTURE Planetary atmospheres;
- 2732 MAGNETOSPHERIC PHYSICS Magnetosphere interactions with satellites and rings