In 2154, the natural resources of the Earth have been depleted. The Resources Development Administration (RDA) mines the valuable mineral unobtanium on Pandora, a moon in the Alpha Centauri star system. Pandora, whose atmosphere is mostly gaseous, is inhabited by the Na'vi, 10-foot-tall (3.0 m), blue-skinned, sapient humanoids that live in harmony with nature. To explore Pandora, genetically matched human scientists use Na'vi-human hybrids called "avatars". Paraplegic Marine Jake Sully is sent to Pandora to replace his deceased identical twin, who had signed up to be an operator. Avatar Program head Dr. Grace Augustine considers Sully inadequate but accepts him as a bodyguard.