Isolation and Abandonment
Throughout The Martian, Mark Watney must contend with the ideas of isolation and abandonment. He is left behind when Ares 3 aborts its mission, even though Watney recognizes, as Lewis and the crew do, that this leaving-behind is necessary for the good of the mission. At times on Mars, Watney recognizes, or re-remembers, how far from Earth he is, and how flimsy his protective sheath truly is. The Hab is only a piece of cloth, after all, and other than the two rovers, essentially nothing else protects Watney from the Martian elements. Secondly, when Watney is able to communicate with NASA (via Morse code, or the Pathfinder's radio), he feels once again connected to human life—and allows himself a more optimistic stance toward his own possible return to Earth. But when this link is severed—as when the drill shorts the Pathfinder's electrical systems—Watney must once again do all he can without NASA's input and advice. Only at the close of the novel does Watney get a way out of his isolation; Beck pulls him back into the Hermes, where he can rejoin his crew-members for their return voyage.
Rationalism and Scientific Thinking
Watney is trained as a scientist and engineer, and he approaches problems on Mars with an orderly, rational mindset. He breaks big problems down into smaller ones, as a way of making sense of them, and he doesn't allow himself to get too worried about theoretical. Instead, he exists in the world of facts: how many calories will he need? How much power does the rover require? Watney's scientific thinking can, at times, seem almost implausible; after all, he must contend with the enormous psychological strain of isolation on Mars (see theme 1). But Watney also knows that no amount of magical or superstitious thinking will get him home. Rather, he must look to his own trove of scientific knowledge, and NASA's guidance, to make his way to Schiaparelli and, eventually, to the Hermes.
Humans vs. "Nature"
Although "nature" is typically represented, in novels, as the non-human parts of planet Earth, in The Martian, "nature" is in fact another planet altogether. And Martian nature is tough. On the surface of the Red Planet, the temperature can plunge at night, there's essentially no oxygen, and nothing can grow in the soil. In order to survive, Watney must "re-engineer" parts of nature to suit his purposes: he grows potatoes in the Hab, and figures out a way to create more water, performing a chemical reaction on leftover jet propellant. Watney knows that he won't be able to defeat Mars's difficult nature, but he can outwit it, as when he avoids the dust storm at the end of the novel, on his trip to Schiaparelli.
Patience and Foresight
Watney's time on Mars requires an enormous amount of planning, patience, and foresight. Even before the Ares 3 trip occurs—before the emergency that strands Watney on Martian soil—NASA has spent years working out the technical details of deep space travel, from the largest to the smallest problems. Once on Mars, and without his fellow crew-members, Watney doesn't jettison NASA's careful, stagewise planning. Instead, he leans into this process, taking large problems and going at them systematically, with checks and double-checks in case he's made any mistakes along the way. This patience is perhaps one of Mark's strongest qualities, the thing that allows him to wake up each morning and continue chipping away at the cosmically complex challenge of making his way back to Earth from Mars.
Risk-taking
As a counterbalance to patience and foresight, however, the novel also thematizes risk-taking. This is most pointedly illustrated in the exchanges between Sanders and fellow NASA administrators when they are deciding between the resupply mission with the Taiyang Shen rocket and the ostensibly "riskier" Purnell Maneuver. Although the latter comes from out of left field—beyond the typical checks and balances of NASA's idea chains—it is, in a sense, the less "risky" option, because it has a higher tolerance for variation built into it. It is "riskier" because it is untested, but in taking this risk, NASA winds up increasing, rather than decreasing, Watney's chances of survival. This kind of strategic risk-taking goes hand-in-hand with patient planning. As Watney illustrates while on Mars, sometimes a person must think entirely outside the box in order to reimagine, and solve, an otherwise intractable problem.
Exploration and Adventure
Watney is on Mars in the first place because of his, and NASA's, spirit of adventure. Just like the sea voyages that form the basis of many 17th- and 18th-century narratives, space voyages become a cornerstone of "science fiction" literature in the 1900s, just as human beings develop means of flying on Earth, and of flying beyond Earth's atmosphere. Human beings are on Mars because of this overall spirit of adventure and exploration: because it is difficult to land and live on another planet, and therefore inherently worth trying to accomplish. Never once on his journey, tellingly, does Watney question his reasons for joining the mission to Mars. He is content with the spirit of adventure that put him on the Red Planet initially—even though it has nearly killed him.
Individuals vs. Bureaucracies
Throughout the novel, too, the idea of individuals and bureaucracies runs like a thread. Watney likes to do things his own way, and it is partially this initiative that makes him a good astronaut: he's not afraid to take risks, he's creative, and he thinks for himself. But NASA is also a giant bureaucratic structure with more than one constituency. Namely, NASA also faces "outward," toward non-astronaut citizens of the US and the world, who might wonder why NASA does what it does—and these worries cut across the explorer's instincts many astronauts have. This is dramatized most clearly in the novel in the section on the Purnell Maneuver, when Henderson and the crew wish to carry out a decision that Sanders, looking to protect the organization, frets over.
