Jupiter Weapon Skin for Gears of War Ultimate Edition
Unlocking the Jupiter weapon skin is only possible if you played day 4 of the Gears of War Ultimate Edition beta.
The Jupiter skin is a rare skin because it is only possible to obtain on one day of the Beta of Gears of War Ultimate Edition. In order to unlock it you would have participated in the Beta on this day.
It is unlikely that you will come across the skin very often in game, as there are so many skins and this skin in particular is quite difficult to obtain.