@aworldinpages if they're, there's a lot we don't know about planet formation.Mercury is obvious, it's simply a smaller earth; Venus is Earth after an apocalyptic climate change begins fueling itself; Mars is an Earth with an eroded atmosphere; Jupiter and Saturn cannot be explained with our current theories; Uranus is Earth if it was hit by a lot of ice asteroids, enough to hide the sun for a couple decades; and Neptune is the same, except hotter.