The methane-based hydrologic cycle on Saturn’s largest moon, Titan, is an extreme analogue to Earth’s water cycle. Titan is the only planetary body in the Solar System, other than Earth, that is known to have an active hydrologic cycle. With a surface pressure of 1.5 bar and temperatures of 90 to 95 K, methane and ethane condense out of a nitrogen-based atmosphere and flow as liquids on the moon’s surface. Exchange processes between atmospheric, surface and subsurface reservoirs produce methane and ethane cloud systems, as well as erosional and depositional landscapes that have strikingly similar forms to their terrestrial counterparts. Over its 13-year exploration of the Saturn system, the Cassini–Huygens mission revealed that Titan’s hydrocarbon-based hydrology is driven by nested methane cycles that operate over a range of timescales, including geologic, orbital (for example, Croll–Milankovitch cycles), seasonal and that of a single convective storm. In this Review Article, we describe the dominant exchange processes that operate over these timescales and present a post-Cassini view of Titan’s methane-based hydrologic system.
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A.G.H. acknowledges the support of NASA Cassini Data Analysis Program grant NNX15AH10G and NASA Early Career Fellowship grant NNX14AJ57G. R.D.L. acknowledges the support of NASA Outer Planets Research grant NNX13AK97G. J.I.L. is forever thankful to the Cassini Project for long-term fiscal ministrations. We also thank J. M. Lora for helpful insights and discussions.
The authors declare no competing interests.
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Hayes, A.G., Lorenz, R.D. & Lunine, J.I. A post-Cassini view of Titan’s methane-based hydrologic cycle. Nature Geosci 11, 306–313 (2018). https://doi.org/10.1038/s41561-018-0103-y
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