I am not an astronomer (save in the very amateur sense), but I think it has to do with Jupiter forming both early in the history of solar system, and, as you gu

I am not an astronomer (save in the very amateur sense), but I think it has to do with Jupiter forming both early in the history of solar system, and, as you guess, beyond the Sun's 'snow line'. Wikipedia is a good place to start getting a feel for the possible history of the Solar System: https://en.wikipedia.org/wiki/Jupiter#Formation_and_migration https://en.wikipedia.org/wiki/Jupiter#Formation_and_migratio... https://en.wikipedia.org/wiki/Grand_tack_hypothesis https://en.wikipedia.org/wiki/Grand_tack_hypothesis https://en.wikipedia.org/wiki/Nice_model https://en.wikipedia.org/wiki/Nice_model