I just finished an online course on the science of the solar system, taught by Mike Brown (alias Plutokiller) of Cal Tech. It was pretty great! I learned a lot. Brown did an excellent job presenting it — as I couldn’t help but notice from the few guest lectures along the way; they weren’t bad, but I kept wishing they were as good as Brown’s. (Pro tip: Look at the camera, guys!)
I feel like I now know more (or perhaps I should say, am less ignorant) about Martian geology than terrestrial, which leads me to think maybe a geology course sometime.
Also, as an indirect result of taking this course, I now own a chondrite and an iron meteorite. No achondrites, no pallasites, yet.