A team of international astronauts are sent on a dangerous mission to reignite the dying Sun with a nuclear fission bomb in 2057.
50 years into the future, the Sun begins to die, and Earth is dying as a result. A team of astronauts is sent to revive the Sun - but the mission fails. Seven years later, a new team is sent to finish the mission as mankind's last hope.
Space-ship Icarus I failed to kick-start Earth's dying sun back into action and disappeared. Icarus II carries the last available nuclear super-bomb on a mission to try again. The navigator's oversight causes serious damage to the ship, yet returning is no longer a hope, the mission dubious. Having picked up Icarus I's emergency signal from Mercury, they decide to try pick up its bomb. That side-trip comes at a high cost. But an even worse surprise is lurking aboard.
The sun is dying, which means that life on Earth will eventually die along with it. In 2050, Icarus is the name given to a human space mission to approach the sun in order to bomb it to reignite it. Icarus disappeared without a trace, unable to complete the mission. It's now 2057, and Icarus II, with an eight person crew, each crew member with a specific role, is making one last attempt to resurrect the sun. As Icarus II reaches the far side of Mercury, the crew members discover a distress signal from Icarus I. After a debate on the pros and cons of doing so still with the primary goal of completing their mission first and foremost among the team as a collective, the crew aboard Icarus II decide to approach Icarus I both in a hope to find survivors aboard and to use their payload as extra insurance in completing their mission. However, making this change in course has inherent risks in and of itself, those risks which the naysayers used in their argument, some with the ulterior motive of self-preservation. This change does have unintended consequences which leads to the team needing to make further decisions which could sacrifice certain crew members. But what they may also discover is the reason that Icarus I failed in its mission, which could mean life and death for them and as such life and death for those on Earth.
In the future, the sun is dying and Earth lives another glacial period. After the failure of the Icarus Mission, a team of eight astronauts are sent to the sun in the Icarus II Mission to explode a weapon generating a supernova within the sun in the last hope of planet Earth. However, when a crew-member commits a mistake in the operation of the aircraft shield, he jeopardizes the survival of the group.
- In the year 2050, dark energy is destabilizing the sun, threatening all life on Earth with a new ice age. Scientists conclude that an experimental stellar bomb payload, with a mass equivalent to Manhattan Island, will flush out the infection and restabilize the sun. The Icarus I, a prototype spacecraft with advanced heat shielding and a sophisticated artificial intelligence (AI), is tasked with the arduous journey of transporting the payload. Unfortunately, the mission fails.
Seven years later, a second attempt is made with the Icarus II. The crew consists of Dr. Robert Capa (Cillian Murphy) - the physicist overseeing the final calculations for the stellar payload's deployment and detonation; Captain Kaneda (Hiroyuki Sanada) - the focused, determined mission leader; Mace (Chris Evans) - the engineer who lends a military perspective to the mission; Dr. Searle (Cliff Curtis) - the ship's counselor and medical officer; Cassie (Rose Byrne) - the pilot who serves as the crew's emotional tether; Trey (Benedict Wong) - the tech savvy navigator; Harvey (Troy Garity) - the first officer and communication specialist; and Corazón (Michelle Yeoh) - the botanist who maintains the oxygen garden that provides both food and carbon to atmosphere recycling during the trip.
After 16 months of travel, as the ship nears the sun, solar noise known as "the dead zone" begins to interfere with radio communications to Earth. As the ship encountered the "Dead Zone" seven days earlier than expected, the crew is now left with just 24 hours to collect all of their individual thoughts and send each of them off to their loved ones in a last message "packet".
Capa has difficulty in finding his words, and makes several different attempts at his message, unintentionally "running out the clock" on Mace. A fight breaks out between Capa and Mace, which lingers as open animosity between the two, despite Mace's apology. Searle has Mace spend a couple of hours in the "Earth" room, which simulates sensual experiences on Earth. Afterward, Mace apologizes to Capa and they become civil toward each other.
When the crew meets to discuss their latest progress, Corazón notes that while the ship is only about two-thirds of the way to its destination [the sun], the garden has been producing oxygen at better than expected rates - the ship already has enough oxygen stored up for the delivery, and a quarter of the return trip.
Searle has become fascinated at looking out from the ship's viewport at the approaching sun and is curious what it would be like to experience the unfiltered view. The AI (voice of Chipo Chung) warns him that he can only tolerate 3.1% of the actual light, and Searle has Icarus set the system for 30 seconds of viewing at that rate. The result has some kind of effect on Searle, who begins to spend many hours in the viewing room, repeating his exposures to the sun so often that his skin eventually peels away and sores cover his face.
Captain Kaneda has been researching the video logs of Captain Pinbacker (Mark Strong), the commander of Icarus I, in an attempt to discover why the original mission failed, and thereby prevent his crew from making the same errors. He plays one video where Pinbacker describes a small meteor storm that did superficial damage, and is puzzled by Pinbacker's aloof reaction to the event.
As the ship approaches Mercury, Harvey picks up a signal from the Icarus I's distress beacon, only hearing the faint signal because it was amplified by the iron in Mercury's mass. Emphasizing that some of those aboard Icarus I could still be alive, Captain Kaneda explains this point to the crew, and begins a discussion as to whether the current mission should be altered in order to check on the Icarus I's distress beacon. Mace is not happy with the choice to divert from their flight path because their mission to deliver the bomb has the utmost priority.
Dr. Searle says that he agrees with Mace's assessment, but adds that diverting to the Icarus I could possibly add a second payload [bomb]. He argues that since the Icarus bombs have never existed before and therefore have never been actually detonated either, their existence is "entirely theoretical" and having two could be advantageous if something went wrong with the first one. There is further heated discussion, which Captain Kaneda finally stops by saying he is handing the decision to the ship's most informed person in these matters, their nuclear physicist, Capa.
Capa is troubled by being asked to make this decision. He explains to the captain that he simply doesn't have enough information to make an informed and rational decision, and the best he can do is to "flip a coin." When Kaneda asks "So? Heads or tails?", Capa replies, "Heads: two last best chances are better than one."
Capa's decision is finalized by the captain: both Icarus crafts will rendezvous together. Trey plots the course, checks it three separate times, and is satisfied he has been accurate. Trey shifts the Icarus II's course to intercept the Icarus I. In the many calculations, Trey misses one - the need to readjust the heat shield that protects the ship from the sun's radiation. This error is discovered when there is an emergency declared by the computer after slight damage to the heat shield results from Trey's mistake.
The true extent of the damage can only be assessed and repaired by leaving the ship and working directly in space. Captain Kaneda asks for a volunteer to accompany him and, after refusing to allow the second-in-command to join him, Capa is volunteered by Mace (Mace's way of stating that the current events are a direct result of Capa's decision to alter the original mission, and the "volunteering is clearly made in anger and not by deciding if Capa was the best man for the job.") Nevertheless, Capa accepts the implicit challenge, and Kaneda agrees to let him accompany him on the spacewalk.
As Captain Kaneda and Capa exit the ship in EVA suits to begin repairs, Cassie moves the Icarus II's position so as to provide the two spacewalking astronauts as much "shade" as she can. She does this knowing it will result in the loss of the two communications towers needed to return to Earth later. The tips of the comm towers burn up as they continue to revolve around the living quarters, in and out of the sunlight. Consequently, Cassie unwittingly sets off another chain of events, when the still revolving and burning remnants of the communications tower causes a beam of sunlight to deflect towards the centre of the ship and onto the oxygen garden. A fire breaks out that initially the ship copes with, but soon it flashes out of control and threatens not only the garden, but the entire ship itself.
Corazón rushes to her rapidly burning garden and requests entry, thinking she can save it but Mace, weighing up the situation quickly, realizes that the mission and ship will be lost unless drastic action is taken so he orders the computer to release all the stored oxygen in the tanks, to provide such an enormous boost to the fire that it will literally "blow itself out"; however, knowing too that this will completely destroy the garden.
During this event, the AI begins to take automatic control of the Icarus II, in order to return the heat shield back to cover the living quarters as continued exposure threatens the mission (which due to Cassie is now protecting the two astronauts from being vaporized by mere direct exposure to the sun). Cassie realizes that this maneuver will result in the death of the two spacewalkers and she tries to countermand the order, but the AI refuses to be ignored.
Cassie and the AI fight over control for a few moments, with Cassie eventually using an override command that needs to be authorised by a second crew member. Cassie turns to Mace to have him say his authorisation code but he refuses - he believes the mission far outweighs the loss of Kaneda and Capa. Cassie pleads with Harvey, who immediately issues his authorisation.
Silently disagreeing, Mace directly calls Captain Kaneda and asks him to support him, countermanding the orders issued by Cassie and Harvey - a decision that will result in his own (Captain Kaneda's) death and of Capa. Kaneda agrees with Mace that the mission is more important than his and Capa's life and the Captain tells the AI to resume corrective shading and proceed with the mission, which it does.
As the cover for the two astronauts is dimished, Kaneda orders Capa to go back to the ship as he patches the last of the heat shield damage by himself. Capa complies, and shortly after Kaneda fixes the remaining damage and then meets his demise with exposure to the sun.
Because of the loss of their oxygen garden, the astronauts now have no choice but to intercept Icarus I. Trey still blames himself and is put on suicide watch.
Now alongside Icarus I, Searle, Capa, Mace and Harvey board to discover that there is enough food to last; a flourishing oxygen garden and a workable payload. However, there has been extensive damage to the ship's computer servers which will not allow the ship to move. A video log from Pinbacker, now sporting signs of disfigurement, suggests that the crew chose to scrub the mission, believing that humanity's impending destruction was God's will. Additionally, all crew members are found burned to death in the viewing room, the result of the filter having been turned off. The comment is made that if the Icarus I were not behind the shield of Icarus II, those seeing the burned crew members would suffer the same fate.
While the crew are investigating, the airlock connecting the Icarus I to the Icarus II is mysteriously destroyed and both ships are pulled apart. They find one EVA suit that would let Capa go back (as he is the only one able to deploy the payload) to Icarus II. Harvey disputes Capa being given the suit because of his status as Captain following Kaneda's death. Searle stays to manually open the shafts while Harvey and Mace use the insulation of the ship to cover themselves so they can hold onto Capa as he is shot towards the Icarus II and make it in themselves. During the actual trip, Capa loses his grip on Harvey, who drifts off into outer space and is frozen. His body can be seen breaking apart when it collides with the ship and burning up when his corpse leaves the protection of the heat shield. Mace suffers frostbite but lives and rapidly recovers.
As Icarus II leaves, Searle enters Icarus I's viewing room to prepare for his death, for when Icarus II leaves, there will be no shielding from the sun. He burns to death as the Icarus I crew did.
Corazón calculates how much oxygen they have and how much they need to complete the mission. She concludes there is enough for four of the five of them to live to deliver the payload. It is decided Mace will kill Trey but when he goes to carry out the act, he finds Trey has already committed suicide. Mace very viciously smears blood on Capa's hand, blaming him for Trey's death and again the two fight, a battle that ends quickly in the low oxygen environment of the ship.
In the payload room, the AI tells Capa that there is still not enough oxygen for all of them to live until they deliver the payload. He says that Corazón did the math and there should be enough oxygen for all four surviving crew members. The AI tells him that there are five people on board the ship, the fifth being in the viewing room. Capa races to the viewing room and discovers that Pinbacker is still alive. He is terribly burnt everywhere on his body and is clearly psychotic. He slices a wound in Capa's chest with a stolen scalpel and chases him through the ship. Capa makes it to the EVA suit room and locks himself in. Pinbacker pulls the safety lever, trapping Capa in the room. Pinbacker then removes the ship's computer servers from their coolant just as he did on his own ship.
In the burned-out oxygen garden, Corazón finds a single seedling rapidly growing out of the newly burnt soil, giving her and the mission hope of not just survival but even returning to Earth. As she calls Capa and Cassie to the room, Pinbacker kills her. Mace goes into the cooling unit to fix the Icarus II's mainframe by immersing himself in the coolant. He is caught in the machinery, his leg injured and bleeding, and he eventually freezes to death. Pinbacker also chases Cassie, who hides in the front of the ship, in the nuclear payload.
Trapped in the EVA suit room, Capa talks to Mace before he dies. Mace, in agony from the freezing coolant, tells Capa he'll have to manually decouple the nuclear payload from Icarus and fly it directly into the sun. Capa escapes from the room by donning an EVA suit, puncturing the inner door with a welding torch and releasing the outer airlock door. Many of the ship's loose contents and Corazón's body fly out of the ship and Capa gains access. He decouples the payload and walks to the front hatch of the ship. As the payload and Icarus II drift apart, Capa uses the propulsion unit of his EVA suit to fly to the payload. As he reaches it, the payload's thrusters fire, burning up part of Icarus II. The rest of the ship burns up and explodes.
Capa goes into the payload to manually pilot and ignite it. There he finds Cassie hiding and is confronted by Pinbacker. The two grapple with the psychotic Pinbacker and escape his clutches. Capa manages to ignite the payload and as the nuclear reaction begins, he finds peace, accepting his death and staring into the flames of the sun as it looms ever closer.
Back on Earth, Robert Capa's sister (Paloma Baeza) and her children (Archie and Sylvie Macdonald) are outside in a park covered with snow as she watches the last message sent to her by Capa. A brighter than usual sun is seen finally breaking through the clouds over a frozen Sydney Harbour, showing that they succeeded in their mission.