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Why Titan and Enceladus ?
| Indeed, Titan's dense atmosphere has been penetrated by Cassini-Huygens to reveal a complex world with diverse geophysical and atmospheric processes reminiscent of those on Earth, but operating under very different conditions from our home world. Titan also possesses a methane cycle remarkably analogous to the hydrological cycle on the Earth but with the fluid ocean removed. Fluvial features, lakes, clouds and tentatively rain may exist, but the working fluid is methane and its photochemical product ethane. Tantalizing but circumstantial evidence exists for a form of volcanism involving water ice and possibly ammonia. In the upper atmosphere (up to at least ~1100 km) photochemistry driven by ultraviolet light and charged particle chemistry produce suites of complex heavy hydrocarbons and nitriles, affecting the thermal balance and chemistry of the whole atmosphere. Cassini data suggest that Titan's climate has not been static over much of the history of the Solar System and may still be changing today. The ultimate source of methane and the sink for its organic products are key outstanding questions about this cryptic world. |  |
 | Enceladus, only ~500 km in diameter, is a puzzling moon with dramatic jets of organic-laden water vapour and dust-sized icy particles emanating from its south polar region, possibly from liquid water reservoirs, and "feeding" Saturn's E ring. Enceladus' jetting activity, the mechanism responsible for this activity, and the moon's astrobiological potential are of primary interest, as are the long-term variability of Saturn's magnetospheric plasma, neutral gas, E-ring ice grain density, radio emissions, and the co-rotation of Saturn's planetary magnetic field in response to the active jets. |
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