Planet postion in a solar system seems to be up to chance. Is Earth lucky or made special?-"Horner emphasized that the numerous simulations his team ran on Jupiter's influence in the solar system shows that where planets end up is often a result of chance as much as physics. -"Every object you add to [a planetary] system adds complexity, and the end result is a result of random chances," said Horner. "So if you change something very small when the solar system is forming, it's kind of chaotic.'"- Read more at: http://phys.org/news/2014-04-mighty-jupiter-earth-habitability.html#jCp