Less than two months prior to the game's release, Xbox360achievements obtained the full achievements list for the Xbox 360 version of Portal 2. The "leak" has thus sparked rumors that Portal 2 may tie into the long-awaited third episode of Half-Life 2.
Although the wait hasn't reached Duke Nukem Forever standards, players haven't seen any sign of Half-Life: Episode 3 since the second chapter was released back in 2007. Last year we were crossing our fingers that Valve's big E3 2010 reveal would be the long-delayed Half-Life 2 episode, but as it tuned out, it was an announcement regarding Steam on the PlayStation 3 version of Portal 2. That was definitely big news in regards to cross-platform play between PC, Mac and console, but not as huge as a possible Episode 3 reveal.
Nevertheless, what has sparked the current Episode 3 rumor is the "Ship Overboard" achievement with the "Discover the missing experiment" requirement. This may be a possible reference to the Borealis, an Aperture Science vessel carrying dangerous and experimental cargo last mentioned in Episode 2. In a rush to beat Black Mesa for funding, Aperture ignored safety protocols and the ship disappeared, taking the crew and parts of the dry dock to wherever it went. The Borealis is expected to make an appearance in Episode 3 thanks to previously leaked concept art.
Unfortunately, the achievement could have nothing to do with Half-Life2: Episode 3. The achievement undoubtedly refers to a specific task in Portal 2, and could possibly pay tribute to Valve's other popular franchise in name alone. Then again, developers have a dark sense of humor, dropping hints here and there on a possible, unconfirmed project, torturing poor gamers as they bang their heads on desks trying to decrypt clues.
Let the speculation and head wounds begin.