The Martian opens with the Sol 6 log entry of astronaut Mark Watney, who is the resident botanist and engineer on NASA’s Ares 3 mission to Mars. Watney explains that, while the crew was supposed to spend a month on Mars, they were forced to abort the mission early. This was due to a sandstorm with violent winds that threated to damage the MAV (Mars Ascent Vehicle), which the crew needed to return to their ship, Hermes. As the crew moved from the Hab to the MAV, the Hab satellite communications dish was blown through the air and its antenna punctured Watney’s EVA suit and cut into his side; Watney passed out. Believing him to be dead, the rest of the crew returned to Hermes, leaving Watney behind on Mars with no way to communicate with the ship or with NASA. After regaining consciousness, Watney returned to the Hab (the mission’s base on Mars), tended to his wounds, and began to make a plan that would allow him to survive until NASA could orchestrate a rescue.
Watney rations his meals and finds a way to grow food on Mars. As the mission’s botanist, Watney brought a small amount of Earth soil with him. He begins saving his feces and the leftovers from his meals to use as “compost,” then he mixes the compost with Martian soil and Earth soil, converting it all to crop soil. While most of the mission’s meals are freeze-dried, NASA sent a few whole potatoes that the crew planned to use for a Thanksgiving dinner; instead, Watney cultivates the potatoes in the Hab and in two emergency pop-tents attached to the mission’s rovers. To entertain himself, Watney browses through the media files that the other members of the crew brought with them. He starts watching Commander Lewis’ collection of dated 1970s television shows and listening to her disco music.
In order to irrigate the crops, Watney needs to make water. He uses the Hab’s oxygenator to convert carbon dioxide from the MAV’s fuel plant into oxygen. Then, he converts hydrazine fuel into nitrogen and hydrogen in order to slowly burn the hydrogen in the presence of oxygen, which makes water. At first, Watney seems to be making water successfully, but he soon realizes that not all of the hydrogen has reacted to make water—some of it is lingering in the Hab’s atmosphere. Since hydrogen is highly flammable, this is very dangerous; Watney has turned his habitat into a giant bomb. Watney solves this problem by tricking the Hab’s oxygen regulator into pulling all the oxygen out of the Hab. While wearing a space suit, he uses an oxygen tank to burn off the hydrogen in controlled bursts.
The novel then shifts to a third-person omniscient narrator on Earth, where NASA director of Mars operations Venkat Kapoor and NASA Administrator Teddy Sanders have just attended Watney’s memorial service. Venkat wants to assess the damage and see if some of the leftover supplies from the Ares 3 mission could be used for a future, not-yet-funded Ares 6 mission. Teddy initially refuses, explaining that images of Watney’s body would only bring more bad press coverage, but Venkat counters that the images could actually sway public opinion (and thereby, Congress) in favor of a sixth mission to Mars that could recover Watney’s body. Teddy agrees.
When SatCon employee Mindy Park doesn’t see Watney’s body in the photos, she realizes that he is still alive. She notifies Venkat, who calls a meeting with Teddy and director of media relations Annie Montrose. They decide they’ll take the news public in 24 hours. Teddy decides not to inform Commander Lewis; the news could distract the Ares 3 crew, and Teddy is not prepared to risk their safety. Though they cannot communicate directly with Watney, NASA begins tracking him with Satellite imagery and starts developing a rescue plan. CNN launches The Mark Watney Report, a daily show covering the story. It’s the biggest news story on the planet.
The novel once again takes up the log-entry structure. Watney has developed daily routines and is successfully growing potatoes. His new goal is to find a way to get to the Ares 4 MAV at the Schiaparelli crater, 3200 km away. He’ll have to cross the relatively flat Acidalia Planitia, and then the remaining, more rugged territory. To do so, he’ll need to modify the rover for a long trip. After some short test drives, Watney decides that he’ll heat the rover using the RTG (radioisotope thermoelectric generator), a box of highly unstable radioactive plutonium. NASA uses RTGs to power unmanned probes, and, on the Ares missions, to power the MAV before the crew arrives. Upon the Ares 3 crew’s arrival, Commander Lewis removed and buried the RTG. Watney digs it up and moves it to the rover. With the rover modifications complete, Watney starts planning for a twenty-day trip. Watney tells us he has a specific goal for the trip, but he doesn’t say what it is.
On Earth, Mindy attends a meeting with NASA’s top management, including Teddy, Venkat, Annie, JPL director Bruce Ng, and Ares 3 flight director Mitch Henderson. Mitch challenges Teddy’s decision not to inform the Ares 3 crew that Watney is alive, but Teddy does not change his mind. The team discusses their plan to keep Watney alive long enough for rescue by speeding up the process of making the Ares 4 pre-supply probe and sending it to the Ares 3 site. Later, after reviewing satellite images and mapping Watney’s coordinates, Mindy and Venkat realize that Watney is headed to Pathfinder, an unmanned probe that NASA lost contact with in 1997. If Watney can get its communication system online, he can talk to NASA.
The novel shifts back to Watney’s log. He reaches Pathfinder, loads the small Soujourner rover and the larger Pathfinder probe (the part with the radio) onto the rover. After he returns to the Hab, Watney successfully repairs the Pathfinder and Sojourner. Pathfinder acquires a signal. On Earth, NASA’s staff celebrates. Watney and NASA begin exchanging messages using a complicated system relying on Pathfinder’s camera. Soon, software engineer Jack Trevor finds a way to hack Pathfinder’s software so that Watney can send and receive emails in the rover. Teddy gives Mitch permission to inform the Ares 3 crew that Watney is alive.
Weir shifts the novel back in time to the morning of Sol 6, showing readers the rest of the Ares 3 crew’s experience of the sandstorm and Watney’s apparent death. Then, Weir moves back to the “present,” where the crew on Hermes receive a voice message from Mitch, telling them Watney is alive. Most of the team is overjoyed, but Lewis blames herself for giving the order to abandon Watney.
Though Watney is glad to be able to communicate with NASA, he now feels that NASA is micromanaging his work. On Sol 119, as Watney exits the Hab through Airlock 1, the Hab canvas breaches, and the Airlock is torn from the rest of the Hab. In the following days, Watney manages to repair the Hab, but the soil and young potato plants are now dead. The supply probe will arrive Sol 856, but, with the potatoes dead, he only has enough food to last until Sol 600. Back at NASA, the usually-cautious Teddy decides that in order to get the Iris supply probe to Watney in time, they’ll skip standard inspection procedures. By doing so, they launch the probe with a faulty bolt that comes loose, throwing the probe off-balance. Iris crashes into the ocean.
Guo Ming, director of the China National Space Administration reaches out to Teddy and offers to allow NASA to modify the Chinese probe Taiyang Shen to send supplies to Watney. Meanwhile, astrodynamicist Rich Purnell has found a way to get Hermes back to Mars in time for a flyby on Sol 549. The “Rich Purnell Maneuver” uses Taiyang Shen to send Hermes a resupply probe. Watney would have to get to the Ares 4 MAV, modify it, and use it to reach Hermes. Teddy has to choose between the Purnell Maneuver and Iris 2 (the plan to send Watney food on the Taiyang Shen). Though the Purnell Maneuver is more likely to succeed than Iris 2, it risks 6 lives rather than 1. Teddy chooses to stick with Iris 2. Mitch, convinced Teddy has made the wrong choice, leaks the Purnell Maneuver to the Hermes crew. The crew decides to go against NASA’s orders and executes the Purnell Maneuver.
NASA informs Watney of the new plan, and Watney begins modifying both rovers in preparation for his trip to the Ares 4 MAV: he turns one into a trailer so that he can carry the “Big Three” (the atmospheric regulator, oxygenator, and water reclaimer) with him. While working on the modifications, Watney accidently sends an electrical charge to Pathfinder’s hull and fries its electronics. There is no way to get Pathfinder back online. Watney spells out Morse code messages to NASA using rocks and continues on with the rover modifications.
Meanwhile, on Hermes, the Taiyang Shen resupply probe successfully docks, and Johanssen and Beck are falling in love.
Once Watney connects the rovers, he builds a “bedroom” tent out of canvas that attaches to the rover’s airlock. Then, he sets out for Schiaparelli and the MAV 4 site. Venkat realizes that Watney’s path will take him through a dust storm in Arabia Terra that will block eighty percent of sunlight, leaving him without enough energy to even run life support. The change will be so gradual that Watney likely won’t notice until he’s fairly far into the storm. Watney begins to notice that his batteries aren’t holding a charge as well as usual, and he eventually realizes that he’s in the dust storm. Watney determines that the storm is north of him and moving west; he can avoid the storm by traveling south, then east. Since Schiaparelli is to the southeast, Watney won’t have to go too far out of his way.
Watney successfully circumnavigates the dust storm, but as he drives into the Schiaparelli crater, the rover rolls, and the trailer breaks loose and flips. Within three days, Watney manages to get the rover and trailer upright and replace the tow hook. He continues to the Ares 4 MAV. Once there, he can use the MAV’s radio to communicate with NASA and with Hermes. Bruce and Venkat instruct Watney on how to modify the MAV and electrolyze his water and urine to create more hydrogen fuel. To lighten the MAV, Watney removes all nonessential gear, backup comm systems, and all life support—he will wear his EVA suit for the launch. Martinez will pilot the MAV remotely, so Watney removes the controls. Finally, Watney removes the nose of the ship and covers the hole with Hab canvas. During the launch, the canvas breaks free and begins to flap, slowing the MAV’s ascent. On Hermes, Johanssen tells Lewis the MAV will reach orbit, but the distance at intercept will be 68 km. They are 39 minutes away from intercept. They can use the ion engines and altitude thrusters to bring them close enough to the MAV to reach Watney at intercept, but they’ll be traveling much too fast. As NASA scientists listen in, unable to help, Lewis orders Martinez to use the ion engines and altitude thrusters. Then, the Hermes crew seal the bridge and reactor room. Vogel builds a pipe bomb and uses it to breach the vehicular airlock on the nose of the ship. The thrust from the escaping air slows the ship enough to make the rescue risky, but possible. When Hermes reaches intercept, Beck leaves the ship on a tether and reaches Watney. The two men return safely to the ship.
On Earth, people celebrate around the world. In Chicago, Watney’s parents embrace. Teddy prepares to brief the press. Back on Hermes, Beck bandages up the ribs that Watney broke during the ascent, and Watney greets the rest of the crew. Watney may be tired, smelly, injured, and hungry, but it’s the happiest day of his life.