No one predicted Mercury would be a planetary core with the mantle stripped off. No one predicted volcanoes on the Jovian moons, or oceans on the inside of them. I can tell you, for every single planet, huge 'we never guessed that' things.
Sol Alan Stern (born November 22, 1957) is an American engineer and planetary scientist. He is the principal investigator of the New Horizons mission to Pluto and the Chief Scientist at Moon Express.[3][4]