I have been having a think about what you could do to urge the player to explore, maybe add a little bit of information about each planet, for example so a planet was made up mostly of magma so you would buy rocks/coal from them at a super cheap price due to the planet being saturated with it, then go across to a cold planet to sell the goods that they themselves can't produce. You could have lots of planet with different specialisations and stats for other things.
Music wise again this could either be set to each style of planet to keep up the atmosphere or you could go down the Sim City route and have lift style lounge music in the background. Just a few thoughts.