My suggestion is that you have to use science modules to learn specific characteristics about the other planets/moons. For example if you set your focus to Duna in the orbit view you can click the info and parameter button on the right to learn about the celestial body. I think it would be neat if specific information like gravity, atmosphere, temperature, escape velocity, etc. had to be learned by sending a probe with the required modules to the planet and report its findings back to Kerbin. Basically things that Kerbals couldn't figure out from observations at Kerbin had to be learned this way. This could be tied into the career mode/contracts as well. I hope this hasn't been suggested before and if it was I apologize. I did a basic search and checked the stickies but couldn't find anything similar.