We have landed multiple rovers on Mars with great success- including the rovers having longer life spans than originally planned for. So what is next? While it does not come out of NASA, there is a group in Europe (Spainmostly) that is currently presenting the idea of landing a boat in one of the large lakes on Titan, Saturn’s largest moon.
If we can land cars on a planet, why not a boat on a moon? We know Titan is covered in lakes and rivers (of methane, apparently, not H20), which makes it a possible location for microbial life.