If we're ever going to explore the only celestial body in our solar system with surface bodies of liquid, we're going to need a sea-worthy vehicle. Luckily, NASA is all over the niche space submarine market.
Titan, a moon on Saturn, has lakes and seas of liquid methane, which NASA is thinking of exploring by 2040. So, instead of rover like the Mars missions use, they will need a submarine. NASA explains the reason for the mission this way:
We propose to develop a conceptual design of a submersible autonomous vehicle (submarine) to explore extraterrestrial seas. Specifically, to send a submarine to Titan's largest northern sea, Kraken Mare. This craft will autonomously carry out detailed scientific investigations under the surface of Kraken Mare, providing unprecedented knowledge of an extraterrestrial sea and expanding NASA's existing capabilities in planetary exploration to include in situ nautical operations. Sprawling over some 1000 km, with depths estimated at 300 m, Kraken Mare is comparable in size to the Great Lakes and represents an opportunity for an unprecedented planetary exploration mission. This mission would be a logical follow-on to a Titan surface mission such as TiME (Titan Mare Explorer) or even a component of a flagship mission of multiple vehicles.
They go on to show that the autonomous submarine, which they show in the concept video, would be doing a lot of heavy science lifting:
The mission concept we propose to study will investigate a full spectrum of oceanographic phenomena: chemical composition of the liquid, surface and subsurface currents, mixing and layering in the "water" column, tides, wind and waves, bathymetry, and bottom features and composition. Measurements of all these aspects of Titan's hydrocarbon ocean environment can only be made through focused in situ exploration with a well-instrumented craft. This investigation represents a significant advancement in our understanding of the history and evolution of organic compounds in the solar system, and hence a critical step along the path to understanding the evolution of life here on Earth and potential life elsewhere in the galaxy.
No word on whether or not the submarine will also be experimenting with Ewok shattering, which is an idea that truly inspires methane lake dreams: