Exploring inside of our planet like we explore the solar system is a frontier that may never be reached. The intense pressure and temperature in the Earth makes it nearly impossible to even conceive of how we could explore much of our planet with our own eyes. That doesn't mean we don't know a lot about the inner workings of Earth, but it takes some circumstantial evidence to pull it off.
If we were to travel from the surface of the Earth to the very middle, we'd travel nearly 4,000 miles. Although that is the same distance as Boston to Helsinki, it is infinitely harder to traverse. In fact, if "straight down" is the direction you want to go, humans have only made it ~7.5 miles -- or a paltry 0.2% of the trek. The hole drilled to that depth was the famous Kola Borehole in northwestern Russia (back when ...
