Wow. I need to rethink how I write about stuff on this thread then. One of the main reasons I love what I do is that I am constantly surprised and amazed by what we keep learning. It never stops, and that is a continuous source of fulfillment, to be even a small part of adding new knowledge and understanding of how things are. I know that many times I write about stuff that is fairly settled, as a form of review I suppose, and if that comes across as "we know everything already" I deeply regret that. I don't want to pontificate; I am filled with wonder on a daily basis, and it's that sense of wonder that I really want to convey and share in this thread and related discussions. So I'll try to do better!
When it comes to space missions, I think it's a true statement that every mission ever flown beyond Earth orbit (as well as a significant number of those themselves) has revealed something highly unexpected or amazing in some way. Now, that's natural to expect in the early days of space exploration when other worlds were being visited or imaged for the first time. But even after that, every mission ends up revealing some new wrinkle that hadn't been considered before.
Now, these aren't radical, oh-my-god-everything-we-know-is-wrong level of surprises. We eventually figure it out, and in the specific case of planetary science, the biggest hurdle to overcome is our natural bias toward viewing everything through our understanding of Earth-- that's only natural. But as we've gotten further and further out into the Solar System, we've been able to observe and understand processes that are simply not possible on Earth, such as whatever shaped this bizarro saturnian satellite, Pan (which means it is Pan-fried gyoza, rather than steamed ). The New Horizons flyby of Pluto is another great example. Nobody expected to find evidence for active, dynamic processes.
So I consider myself lucky indeed to get paid to experience a near-constant sense of awe and wonder, and to help make it possible that people can share those experiences!