Ryland Grace, the sole surviving human astronaut in the Tau Ceti system, makes first contact with an intelligent alien species when he discovers a second spacecraft—the Blip-A—alongside his own Hail Mary. After a series of cautious exchanges using engine flashes and a delivered xenonite cylinder, Grace meets the alien he names Rocky, a pentagonally symmetrical, sonar-using Eridian engineer who is also investigating why Tau Ceti is immune to the Astrophage plague. This event transforms Grace's mission from a solitary suicide quest into a collaborative effort to save both Earth and the Eridian homeworld.

Ryland Grace launches the four beetle probes—John, Paul, George, and Ringo—toward Earth, each carrying a mini-farm of Taumoeba-82.5 and a USB drive of scientific data, after deciding to turn the Hail Mary around to rescue Rocky instead of returning home himself.

Eva Stratt, the Dutch administrator of the Petrova Taskforce, recruits Ryland Grace, a junior high school science teacher, to lead the investigation of the Astrophage samples returned by the ArcLight probe, leveraging his controversial expertise in non-water-based life and overriding his protests with her absolute authority.

Alpha Centauri is a star system that appears in the narrative as part of the evidence that Astrophage has infected multiple stars beyond Earth's sun, confirming the interstellar scale of the threat and shaping the Hail Mary mission's destination.

Amundsen–Scott South Pole Station is the Antarctic research outpost that becomes the site of a controversial nuclear detonation ordered by Eva Stratt and climatologist François Leclerc to release methane trapped in the ice, buying Earth critical time against the Astrophage-driven solar dimming.

Hawaii is the location where Ryland Grace is unexpectedly transported after his successful Astrophage breeding experiment, serving as a brief stopover on his involuntary journey to a Chinese aircraft carrier where the Hail Mary Project is being organized.

Mars is a planet in Earth's solar system that serves as a reference point for interplanetary travel difficulty and as a historical benchmark for the Soviet space program's ambitions during the Space Race. In the context of the Hail Mary mission, Mars is mentioned as a destination that requires less fuel to reach than Venus under ideal conditions, and as the target of a failed Soviet psychological isolation experiment that influenced the decision to place the Hail Mary crew in medically induced comas.

The Pulkovo Observatory is the Russian astronomical institution where Dr. Irina Petrova first detected the anomalous infrared line that became known as the Petrova line, the discovery that revealed the Astrophage infestation of the Sun and triggered the global crisis that led to the Hail Mary mission.

Ross 128 is a star in the local stellar cluster that, according to data analyzed by the Petrova Taskforce, has been infected by Astrophage and is dimming at an exponential rate, confirming that the Astrophage infestation spreads from star to star within a range of under eight light-years.

The Sahara Desert is the vast North African desert that becomes the site of the largest industrial project in human history: the Blackpanel Astrophage-breeding farm. Under the authority of Eva Stratt, the desert is partially paved with trillions of black-anodized metal panels designed to absorb sunlight and breed Astrophage on an unprecedented scale, producing the millions of kilograms of fuel needed for the Hail Mary mission. The project is conceived by the imprisoned engineer Bob Redell and executed by global industrial mobilization, and its environmental consequences—including weather disruption across the Mediterranean and Europe—become a major point of contention within the science team.

Saskatchewan, a Canadian province, was selected by Eva Stratt as the landing site for the ArcLight probe's sample return capsule, chosen for its high latitude, flat terrain, and proximity to San Francisco, demonstrating Stratt's unilateral authority over international space operations.

The South China Sea serves as the primary operational base for Project Hail Mary, where the international scientific team, led by Eva Stratt, conducts the dangerous Astrophage breeding experiments aboard the Chinese aircraft carrier PLAN Gansu, nicknamed Stratt's Vat.

The Sun is the star at the center of Earth's solar system, whose gradual dimming due to Astrophage infection drives the entire plot of Project Hail Mary. Its declining luminosity threatens all life on Earth with an ice age, mass starvation, and societal collapse, forcing humanity to build the Hail Mary and send a crew to Tau Ceti in search of a solution.

Tau Ceti e, renamed Adrian by Ryland Grace, is the third planet orbiting Tau Ceti and the destination of the Hail Mary mission. It is the homeworld of Astrophage and the only planet in the local stellar cluster that remains uninfected by the Astrophage plague, making it the key to saving both Earth and Erid.

Tau Ceti is the star system that serves as the destination of the Hail Mary mission, the only star in the local cluster that remains uninfected by Astrophage despite being surrounded by infected stars, and the site where Ryland Grace discovers the Astrophage predator Taumoeba and makes first contact with the Eridian Rocky.

Threeworld is the third planet in the 40 Eridani system, a small world roughly the size of Earth's moon that serves as the Astrophage breeding ground for Rocky's home star. Its significance lies in its thin but persistent carbon-dioxide-rich atmosphere, which makes it the target for the nitrogen-resistant Taumoeba strain that Grace and Rocky develop to save Erid from Astrophage infestation.

Travis Air Force Base is the U.S. Air Force installation in California where Ryland Grace was flown by helicopter after being taken from his San Francisco lab, and from which he was then flown by fighter jet to Hawaii, marking the first leg of his involuntary journey to the international Project Hail Mary team assembled on a Chinese aircraft carrier.

The alien cylinder is the first physical object exchanged between Ryland Grace and the alien ship Blip-A, serving as the initial medium of communication and the catalyst for first contact. Delivered by a hull-mounted robot, the warm, ammonia-scented cylinder contains a star map model that reveals the Eridians' origin and purpose, establishing a shared understanding of the Astrophage crisis and enabling the two species to begin building a cooperative relationship.

The breeder tanks are a set of xenonite chambers built by Rocky and used by Grace to artificially evolve a strain of Taumoeba resistant to nitrogen, enabling the microbe to survive in the atmospheres of Venus and Threeworld and thus serve as a biological weapon against Astrophage.

The Hail Mary's centrifuge is an artificial gravity system that splits the ship into two halves connected by cables, allowing the crew compartment to spin and simulate Earth-like gravity for sensitive laboratory equipment.

The Chain is a ten-kilometer-long xenonite structure built by Ryland Grace and Rocky to sample the atmosphere of the planet Adrian at the Astrophage breeding altitude, a desperate engineering solution that nearly destroys the Hail Mary but ultimately secures the predator organism Taumoeba.

The Mini-farms are small, hermetically sealed steel capsules designed by Rocky to sustain colonies of Taumoeba-82.5, the nitrogen-resistant predator bred to save Earth and Erid from Astrophage. Each capsule contains a Venus-like atmosphere, a coiled tube of Astrophage as a food source, and a self-regulating population of Taumoeba, engineered to survive the long journey to Earth aboard the beetle probes. They represent the final, portable solution to the Astrophage crisis, but their creation inadvertently reveals a dangerous side effect of the Taumoeba's evolution.

The star map model is a xenonite cylinder sent by the Eridian Rocky to communicate his origin and purpose to Ryland Grace. It is a three-dimensional map of local stars centered on Tau Ceti, with a filament connecting Tau Ceti to 40 Eridani, revealing that Rocky's species comes from the 40 Eridani system and is also threatened by Astrophage. This object is the first successful cross-species communication device, establishing that both parties share the same mission to understand why Tau Ceti is immune to Astrophage.

The National Security Agency (NSA) is a U.S. intelligence agency whose supercomputers and engineers were conscripted by Eva Stratt to model the interstellar propagation of Astrophage, providing the critical data that revealed the infection's spread pattern and identified Tau Ceti as the only uninfected star within range, thereby defining the Hail Mary mission's destination.

The United States Government is a central political entity in Project Hail Mary, depicted as a powerful but ultimately subordinate actor within the international crisis response to the Astrophage threat. It provides critical military, financial, and logistical support to the Petrova Taskforce, yet its sovereignty is consistently overridden by the extraordinary authority granted to Eva Stratt. The government's role illustrates the tension between national power and the necessity of unified global action in the face of existential peril.

CNSA, the China National Space Administration, is the national space agency of China and one of the key international partners in Project Hail Mary, contributing personnel, resources, and industrial capacity to the global effort to save Earth from the Astrophage crisis.

The DGSE (Direction Générale de la Sécurité Extérieure) is the French foreign intelligence service that, in the world of Project Hail Mary, developed a drug capable of inducing retrograde amnesia lasting for weeks. Eva Stratt, the head of the Petrova Taskforce, used this drug to ensure that Ryland Grace would forget his forced conscription onto the Hail Mary mission, thereby guaranteeing his cooperation after waking from his coma at Tau Ceti.

The European Union is a key political and financial entity in Project Hail Mary, contributing to the international effort to combat the Astrophage crisis. It is one of the major powers that fund the ArcLight probe and later cedes authority to Eva Stratt's Petrova Taskforce, demonstrating the unprecedented global cooperation required to address the existential threat.

The United States District Court for the Western District of Washington is the judicial venue where the Intellectual Property Alliance brought a lawsuit against Project Hail Mary, alleging massive copyright and patent infringement. The case became a landmark demonstration of Eva Stratt's absolute authority, as she appeared alone, dismissed the proceedings with a preemptive presidential pardon and an international immunity treaty, and walked out escorted by U.S. Army soldiers, effectively nullifying the legal challenge.

The Department of Energy (DOE) is a United States government agency that, in the context of the Astrophage crisis, becomes a subordinate executor of Eva Stratt's global authority, providing logistical support, military assets, and legal cover for the Hail Mary Project.