He is portrayed by Cillian Murphy.
Capa is the physicist who operates the massive stellar-bomb device. Murphy described the character of Capa as a silent outsider, which was due to the fact that only Capa understood the operation and true scale of the starbomb. Murphy worked with physicist Brian Cox to learn about advanced physics, - who praised Murphy's performance as "brilliant" and a "great portrayal as a physicist" touring the CERN facility and learning to copy physicists' mannerisms. The actor also studied the thriller The Wages of Fear (1953) with Boyle to gain an understanding of the type of suspense that Boyle wanted to create in the film. Murphy said that his involvement in the film caused him to change his views on religion from agnosticism to atheism.
In 2057, the failure of the sun starts a solar winter and threatens Earth. Humanity, in an attempt to reignite it, loads a massive stellar bomb onto a spaceship named Icarus II. The ship is the second and final attempt to save mankind, as the first mission, the Icarus I, was lost seven years previously for reasons unknown.
After losing contact with Earth due to the effects of nearing the sun, Icarus II Communications Officer Harvey discovers the distress beacon of Icarus I while passing Mercury. As the stellar bomb's operation is purely theoretical, physicist Capa recommends to Captain Kaneda they change course; since both bombs depleted all of mankind's fissile resources, a rendezvous with Icarus I would allow two attempts. Mace, the ship's engineer, opposes this plan.
In planning the new course, navigator Trey forgets to realign the shields that protect the ship from the solar wind, causing damage to the shield. Kaneda and Capa embark on a spacewalk to make repairs while the ship is angled away from the sun. However a fire in the ship's oxygen garden caused by reflected sunlight causes the ship to realign and face the Sun, and Kaneda sacrifices himself to complete repairs. Trey blames himself for the loss of Kaneda and the oxygen garden, and psychiatrist Searle assesses him as a suicide risk and sedates him.
Icarus II reaches Icarus I, and Capa, Searle, Harvey, and Mace board the stricken vessel, leaving co-pilot Cassie and botanist Corazon on board Icarus II. While Icarus I has a functional oxygen garden and payload bomb, the ship's computer has been sabotaged, rendering delivery of the second payload impossible. Mace finds a video left by Captain Pinbacker, a radically religious man who states the mission was purposely abandoned by him, thinking it was the "will of God" that humanity should die. The crew of Icarus I is found dead in the solar observation room, having been exposed to un-shielded rays of sunlight. Suddenly, the Icarus I forcibly decouples, destroying the outer airlock and stranding the four crew members on the derelict spacecraft.
Mace suggests that if one crew member stays behind to operate the airlock manually, they can jettison the other three between airlocks by using the vacuum release to propel them; when Searle offers to stay behind, Capa is given the only viable spacesuit, leaving Harvey and Mace with only spare insular materials. Propelled to the Icarus II, Harvey is knocked into space by debris and freezes. Searle, having decided to commit suicide, then enters the Icarus I solar observation room, opens the protective shutters, and is killed by overexposure to sunlight.
Capa, Mace, Trey, Cassie, and Corazon remain alive on board Icarus II. Corazon calculates that, due to the fire in the oxygen garden, the ship lacks the oxygen for five crew members to reach the sun, and the crew discusses killing Trey. With the vote ending up three against one (Cassie), they agree to kill Trey, only to find that he has already committed suicide. During a final inspection, the Icarus II computer then informs Capa that they still lack the oxygen reserves, as a fifth person is on board. Capa ascertains that Pinbacker, now heavily burned from sun exposure, snuck aboard and decoupled the airlocks.
Pinbacker sabotages the spacecraft by removing the mainframe from its coolant bath, shutting down the computer and power systems. He maims Capa, traps him in the airlock, then kills Corazon with a scalpel in what remains of the oxygen garden. Cassie escapes, and Pinbacker chases her into the payload ship, while Mace attempts to undo Pinbacker's sabotage to the mainframe. Manually reactivating the mainframe, Mace is trapped in a coolant reservoir when a mainframe catches his leg, and freezes to death. Capa breaches the airlock's outer door, thereby opening the inner door by decompressing the ship. Manually decoupling the bomb, Capa enters the payload ship, its boosters knocking Icarus II off course and allowing the now unshielded ship to be disintegrated by solar energy. Capa enters the payload and finds Cassie, only to be attacked by Pinbacker. However as the payload turns, Cassie and Capa escape, with Cassie mortally wounded in the process. Capa successfully triggers the payload manually, momentarily distorting space and time and allowing him to watch the interior of the sun enter the room before detonation. On Earth, Capa's sister reviews her brother's last message on the frozen Sydney Harbour and watches the Sun noticeably brighten, implying the mission's success.