I'm currently studying the following diagram:
But I'm not entirely sure I understand what's going on. Is it just, that most exoplanets discovered, is pretty much made up of Hydrogen and Helium ? And then a couple (Like around (1,1)) have the composition like the earth i.e. iron and such.
Basically: The place the planet is located, does that just tell me what most of the planet is made of?
And what is the difference between exoplanets and solar system planets? I thought exoplanets was planets orbiting a star. But maybe the solar system planets are planets within a system of many planets orbiting a sun, and exoplanet only one planet around one star?