Aliens exist, at least in Fallout 3. The fifth DLC pack for the game, Mothership Zeta, which is due out next month, will prove it.
This expansion will take players onto the massive alien Mothership Zeta, hovering miles above the Capital Wasteland. Players will join with other captured NPCs, from the Capital Wasteland and from Earth’s past, and fight their way to the bridge while discovering the aliens' horrible experiments and master plan. New weapons and armor will be available, including the Shock Baton for melee fighters, Alien Atomizer (a pistol), Alien Disintegrator (a rifle), Drone Cannon, a Cryo Grenade (which freezes enemies for a short period of time), Gemini-Era Spacesuit, and Samurai Armor, in addition to new unique weapons and a new heavy weapon. A new perk called "Xenotech Expert" will increase damage done with alien weapons. "Alien Epoxy" will be a new item found in the expansion that can repair an item by 25% even if players do not have a duplicate item. After escaping from the aliens' clutches, players can return to Mothership Zeta if they desire. Four screens from the expansion have been released, and can be viewed here.
Mothership Zeta is scheduled to release on the Xbox 360 and PC on August 3, 2009, and will be priced at 800 Microsoft Points. The expansion is set to release on the PlayStation 3 as well, but does not have a set release date for the platform yet.