The Planets

It's funny how Scientists got all this information about other planets, all over our solar system, but they can't solve anything on this planet let along go to the bottom of our oceans. Science is fantastic, but I don't see how they can know the structural composition of some of these planets in such detail when they're so far away. I Would like to see a video on how they know this because of all I can assume it's temperature based. Why can't we see real footage instead of CGI, it's all assumptions that scientists make. If there was a big bang, did it just blow up little balls of rock into space? It seems to me every time I've watched a rock blow up, there was not one ball-shaped piece to be found, but every part from the big bang is almost perfectly round. What happened to make that possible? How do they know the center of a planet is like. That's so far away, and they are still discovering what our own is like, that makes no sense at all. Why do scientists assume that other planets need to have the same requirements as earth to support life? What if other life forms don't need any of the basic requirements we need to survive? So many questions, how do we know so much information supposedly of each planet if we haven't sent landers there? How do they know what core they have? How do we know the gases that they have?