The phrase in this question is from the treaty made between Spain and Portugal in 1494. Even though it was centuries ago land continues to be divided in a similar fashion. Therefore, I believe that if a new planet were discovered today it's land would also be divided in the same way. The first group to discover would most likely claim it for themselves, a war would then break out for control, which would ultimately lead to a similar treaty being drafted and accepted dividing the land between the parties like it has always occurred.
