Once when I was playing with my friends, we got this question: if you want to move you units to another area on the same planet, do you still need a mobilize order? In my opinion you should use one, but my friend didn't think so because I destroyed his troops!

Page 23 of the rules is pretty clear: "Players use Mobilize orders to move their units to, and/or among, the areas of the active planet." And lower down, it explicitly states that one of the things a Mobilize Order lets you do is "Move friendly units from one or more areas of the active planet to one or more areas on the active planet."

Just as I thinking. Thank you!