| Summary: | With a thick atmosphere, a methane-based hydrological cycle, stable bodies of standing uid at its surface, and many active surface processes, Saturn's largest moon Titan is surprisingly Earth-like. Methane rain on Saturn's moon Titan makes it the only place, other than Earth, where rain interacts with the surface. Looking at Titan is like looking back in time to understand the evolution of present day Earth from early-Earth. This thesis combines several studies related to Titan's hydrologic system, particularly the ways uid interacts with the surface of Titan. Understanding this atmosphere|surface interaction is of great importance to understand Titan's meteorology and evolution. Follwing an introduction about the discovery and need to study Titan, chapter 2 addresses the possible reasons behind Ontario Lacus being the solo lake in the south pole of Titan. In chapter 3 we discuss our novell `wet-sidewalk' observation. Basically if ground gets wetted, and illuminated by the Sun at right geometries we get this broad specular re ection (glint) that's super-bright. That we've seen one near Titan's north pole means that it's rained there now coincident with north polar summer, and furthermore we've got a new technique for monitoring when and where rainfall occurs across Titan's surface. It is extremely dicult to detect rainfall events on Titan due to its thick atmospheric haze and very limited opportunities to view the surface (and its changes). Our wet-sidewalk observation using VIMS |Visual and Infrared Mapping Spectrometer, on the north pole of Titan is the rst of its kind i.e using broad surface re ection and the delayed north polar activity. Hence this observation and the rainfall discovery on the north pole is of extreme importance to understand Titan's climate. While the presence of a hydrological cycle might help explain how the depressions on Titan's surface are lled with liquid methane, the formation mechanisms of the depressions still remain a mystery at the end of Cassini in 2017. We address this question ...
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