The story takes place in planet 4546b's crater, filled with alien lifeforms. 
Plot twist: The crew of the Degasi is still alive.
Aurora survivors: You, Ryler Robinson.
Degasi survivors: Paul Torgal, Bart Torgal, Marguerit Maida.
The planet is infected with an alien virust called the Kharaa. Symptoms: illuminating green spots on the skin, cough. Unless cured the virus is fatal.
Aurora: Giant crash-landed vessel, the drive core is higly radioactive, will explode after a while. In late 2300.