Published in 2021, Project Hail Mary is American author Andy Weir’s third novel, following The Martian (2011) and Artemis (2017). A true example of hard science fiction, Project Hail Mary features Weir’s characteristic combination of humor, scientific accuracy, and technical speculation while incorporating more speculative elements of the genre, notably in its depiction of human contact with extraterrestrial life. Rights to a film adaptation of the book were purchased in 2020.

Plot Summary

In the near future, junior high school science teacher Dr. Ryland Grace wakes up on the Hail Mary interstellar spaceship with total amnesia, the only surviving member of a three-person crew. Gradually, Grace recalls that his controversial academic work on extraterrestrials caused him to be drafted into Project Hail Mary, a mission 12 light-years from Earth to the Tau Ceti solar system to save all of humanity. Earth’s sun is infected with Astrophage, an alien life form that navigates a migration pattern between the sun and Venus via infrared light emission called the Petrova Line. As the Astrophage cause solar dimming, humanity has only 26 years before crop failure, famine, and climate change will reduce the world population by half, and they will ultimately cause total extinction. To save all of civilization, Grace must learn why Tau Ceti is unaffected by Astrophage and send data probes back to Earth. However, the Hail Mary is on a sacrifice mission, as the ship can’t carry enough fuel for a return trip. As the story unfolds in a wry, first-person present tense and alternates scenes from the past and present, Grace recalls discovering Astrophage and preparing for Project Hail Mary as the mission’s lead scientist, and he tries to discover why Astrophage have not destroyed Tau Ceti but seem to be affecting every other star in the local galaxy.

At Tau Ceti, Grace encounters an alien spaceship, the Blip-A, from the 40 Eridani solar system and meets an Eridian, a dog-sized spider-like extraterrestrial with hard mineral skin whom he names Rocky and who is also the only surviving member of his respective crew. After initial communication via scale models, Rocky and Grace learn to communicate verbally with the help of translation software. Rocky’s home star is also infected with Astrophage, and he is at Tau Ceti for the same reason: to learn how to stop Astrophage from destroying 40 Eridiani and all life on Rocky’s home planet with it. Eridians and humans are similarly intelligent, although Eridians are sightless, relying on highly developed sonar senses instead, and are less technologically advanced than humans, although they have perfect memories and highly advanced engineering, and Rocky can produce nearly anything from xenonite, a pure-xenon compound stronger than any material on Earth. Grace and Rocky marvel at their similarities and begin to form a close friendship, sharing a similar sense of humor.

Grace’s memory continues to improve, and the storyline of his remembered past follows his discovery that Astrophage migrate to Venus to breed in the carbon dioxide-rich Venusian atmosphere. Grace works closely with Eva Stratt—the leader of Project Hail Mary who has been granted total authority and immunity by the United Nations—and an international team of scientists aboard a Chinese aircraft carrier to develop an interstellar space ship, create an Astrophage-powered engine, and prepare the crew for their one-way mission to Tau Ceti. As the mission progresses, Stratt justifies increasingly morally complex decisions, ranging from the conscription of unwilling experts to the nuclear bombing of the Antarctic ice shelf to buy Earth more time, all in the name of saving the human race.

Rocky builds a network of tunnels aboard the Hail Mary, and the pair travel to the planet Adrian, which is the other pole in Tau Ceti’s own Petrova Line of migrating Astrophage. The Hail Mary is damaged in a risky mission to collect a sample of Astrophage from Adrian’s atmosphere, and Grace is nearly killed before Rocky risks exposure to Earth atmosphere to save him. Rocky suffers internal combustion due to the oxygen in Grace’s air; Grace, in return, is exposed to the ammonia-based Eridian atmosphere and badly burned as he saves Rocky by returning him to his pressurized compartments. As they both recover from their injuries, Rocky and Grace discover that Astrophage has a natural predator, which Grace names Taumoeba. Taumoeba keep the Astrophage population under control, mitigating its effect on Tau Ceti.

Grace recalls teaching Martin DuBois and Dr. Annie Shapiro about Astrophage and helping to test the equipment for their journey. The mission’s scientist and back-up scientist respectively, DuBois and Shapiro have been chosen for the mission because of a rare DNA sequence that predicts coma resistance, as the Hail Mary crew will be in medically induced comas for the four-year journey to Tau Ceti in order to prevent depression and psychosis. When DuBois and Shapiro are killed simultaneously in an accidental explosion, Stratt forces Grace, who also has the DNA marker for coma resistance, to go in their stead. When Grace resists, Stratt gives Grace a powerful amnesia-inducing drug and has him carried, unconscious, onto the Hail Mary for launch, stopping at nothing to ensure that the mission goes on.

In the present, Grace attempts to reconcile his shame at not volunteering for the lethal-but-heroic mission with his will to survive and desire to save his students’ lives and all of humanity. Grace and Rocky learn that nitrogen is lethal to Taumoeba and begin breeding a nitrogen-resistant Taumoeba strain that can survive the atmospheres of Venus and Threeworld, the infected planet in the 40 Eridani system. Rocky repairs the damage to the Hail Mary and offers Grace his extra Astrophage fuel. Re-fueled and having successfully bred nitrogen-resistant Taumoeba to control the Astrophage on their home stars, Grace and Rocky say their goodbyes.

One month into his return journey, Grace realizes that the nitrogen-resistant Taumoeba have also evolved the ability to pass through xenonite, a side effect of being bred in xenonite tanks. Grace is able to contain the Taumoeba and prevent them from destroying his Astrophage fuel, but he knows that Rocky’s fuel tanks are made of xenonite and Rocky is likely now stranded in space, putting his entire species at risk again. Grace launches the Hail Mary’s four probes, as was originally intended, and turns back to rescue Rocky and take him to Erid, knowing that he will starve when he runs out of food. Grace saves Rocky, who refuses to allow Grace to die and suggests that Grace try eating Taumoeba until Eridians can find a better solution.

Years later, Grace is happily established on Erid, teaching science to young Eridians. He is able to survive on Eridian-made vitamin shakes and lab-grown protein. Rocky visits Grace to tell him that Eridian scientists have determined that Sol, Earth’s sun, has recovered from the Astrophage infestation, indicating that the probes returned to Earth and Project Hail Mary was successful. Grace debates making the long, lonely journey home but puts off the decision as he heads to work teaching.