What are the Auroras, and how do they relate to Mother Brain?
The Metroid Prime 3: Corruption preview channel has been updated with two new movies, one of which reveals some shocking details on what may be a major part of the game's story. The "Spider Ball" video is a demonstration of a large magnetic rail, just like those seen in the first two Metroid Prime games. Samus is first shown traveling between two floating platforms via Screw Attack; the environment appears to be the sky city level shown at E3 2007. On the second platform, Samus goes into Morph Ball mode and begins traveling up a vertical Spider Ball rail. The ability to jump between opposite rails with the Boost Ball, first seen in Metroid Prime 2: Echoes, is used abundantly in this video.
The other video is much more startling for fans of the Metroid series. It is entirely story-based, explaining the origin of the Auroras, organic supercomputers developed by the Federation twenty years before the events of the game. These artificial beings were originally used for scientific purposes but eventually became common in the military and other applications. The Auroras are linked to a massive network with access to a common database. The end of the movie shows a blueprint-style view of Mother Brain's lair from the original Metroid game, labeled "Future Aurora Complex". Mother Brain herself is in the tank on the far left, and we can now see that she looks very similar to the Auroras shown previously in the movie.
Nintendo's official web page for the game explains even more about the story. "The Galactic Federation's network computer, Aurora Unit, is suddenly and completely corrupted with something like a virus. The Federation believes Space Pirates may be behind the problem and are soon attacked. Samus and other hunters leap to their defense only to find that the enemy they face is Dark Samus, armed with immense power that no one can withstand."