You want to find things that don't exist in our solar system at all or are incredibly rare, and then you want to refine and process those raw materials, so that what you send back is the finished product. The least mass for the most buck. So what you want to do is build up an industrial infrastructure on Pandora... you want to tame it. You want to civilize it. And you need workers to do that. Only you can't use humans, because:

A) They cost too much to bring. B) They die in 30 seconds without a breathing mask.

So colonization, in the classical sense, won't work. But wait... you have an indigenous population there. They're primitive, but they have brains and hands, and maybe they can be taught to do the things we need done. We can teach them, and give them cool technology to improve their lives, so they can be healthy and smart, and can all have TV, and in return they will be so grateful they'll not only work in our factories, they'll even build them for us. Groovy.

These are the basic principles of interstellar imperialism, circa 2100 A.D.

Ahead of Prometheus we can see the trinary system of Alpha Centauri... three stars orbiting each other. In the middle, close together, are Alpha Centauri A and B, two yellow main-sequence stars very much like our own star. About 900 billion miles away (a mere stone's throw by interstellar standards... a couple of light-months) is the third star, Proxima Centauri, a runty little red-dwarf.

Standing on Pandora (as you will soon) you can see two disks of light on the horizon at sunset, but never the third, since Proxima is too far away and just looks like a star.

Inside Prometheus, everybody's asleep except for a four man flightcrew who look very haggard. The rest, a hundred or so passengers, are all in medically induced hibernation. With certain drugs people can be caused to hibernate like bears and other mammals, dozing away the years at low temperature, and with minimal mental activity.