Hello, first post here. I'm trying to wrap my head around something here and I'm wondering if anyone can help. I've read that all terrestrial planets have basically the same chemical components - Iron, Silicon, Oxygen, etc - in roughly the same percentages. I also read that the composition of asteroids and meteors (the chondrite designations) aren't a general sampling of mineral content of planetary bodies but refer specifically to the particular bodies that broke up to form such meteors and asteroids. I also also read that in the case of the larger moons of the outer planets, minus the ice, are also made up of generally the same minerals. Now, here's my question - when you hear about Io, you hear alot about sulfur, and when you hear about Titan, you hear alot about Nitrogen. Is that because these bodies have an abnormally high percentage of these materials, or that the particular conditions of these bodies - temperature, tidal stress, etc react primarily on these materials? For instance, if you put our Moon where Io or Titan is, you would see the same types of phenomena, or are these behaviors because of Titan or Io's unique chemical composition? Thanks for any help in advance.