The Science of Project Hail Mary
All the real science from Andy Weir's book, simply explained
Explore the physics, biology, and engineering behind every scene. With interactive simulators, visualizations, and explanations accessible to everyone.
Glossary: Fiction vs Reality
Every term from the book explained: what's real and what Andy Weir invented
What is an Astrophage? Do Eridians exist? Is Tau Ceti a real star? Before diving into the science of each chapter, this glossary explains every important term from Project Hail Mary, who the main characters are, and most importantly, what in the book is real science and what is Andy Weir's fiction.
The Awakening
Induced coma, gravity, and the infrared spectrum
Grace wakes up with no memory in an unknown place. Through homemade experiments, he discovers that gravity is not Earth's. Meanwhile, in flashbacks, a Russian astronomer detects something impossible: an infrared emission line connecting the Sun to Venus.
The Pendulum and the Dying Sun
Pendulums, exponential decay, and extraterrestrial life
Grace builds a pendulum to determine if he's in a centrifuge or a ship. Meanwhile, flashbacks reveal the Sun is losing energy exponentially, and a probe sent to Venus discovers something that will change everything: the dots are moving. They're microbes.
The Astrophages
Extraterrestrial life that devours stars
Grace discovers he's on a spaceship traveling at interstellar speeds. In flashbacks, he examines the Petrova line organisms in the lab and discovers properties that defy known physics: they absorb all radiation, are invulnerable to heat, and store energy at E=mc² levels.
The Hail Mary Ship and the Suicide Mission
Multi-stage rockets, the Tsiolkovsky equation, and climate collapse
Grace explores the full ship and discovers its structure: a survival machine powered by astrophages. With only 40 days of fuel and no return option, he understands it's a one-way mission. On Earth, the effects of the dying Sun are being calculated.
The Life Cycle of Astrophages
Spectroscopy, E=mc² proven, and the salvation project
How astrophages navigate is discovered (following CO₂'s spectral signature), their complete life cycle between the Sun and Venus, and the definitive proof: they convert mass to energy and back, demonstrating E=mc² at cellular scale. Project Hail Mary is born.
The Engines Stop
Time dilation, zero gravity, and first contact
The engines stop and Grace experiences weightlessness for the first time. He calculates the spin drive's enormous power, understands relativistic time dilation, and upon activating the petrovascope discovers something terrifying and wonderful: an alien ship 200 meters away.
First Contact
Trigonometry, spacewalks, and ammonia
Grace calculates the alien ship's size with trigonometry, establishes communication through engine flashes, goes on a spacewalk in an Orlan suit to retrieve a cylinder, and discovers the alien lives in a high-temperature ammonia environment.
The Centrifuge and Xenonite
Artificial gravity, spin drives, and an impossible material
The Hail Mary has an engineering secret: it can split in two and spin like a centrifuge to generate gravity. Dimitri's spin drive demonstrates astrophages' brute power. And the alien cylinder reveals an impossible material: xenonite, made of solid xenon.
The Tunnel
Ammonia as a life solvent, radiative cooling, and contact engineering
The Eridians build a xenonite tunnel between both ships. Grace deduces they live in high-pressure, high-temperature ammonia, confirming life can use solvents other than water. Physical first contact is about to happen.
Rocky
Alien anatomy, base 6, and chord-based communication
Grace sees Rocky for the first time: pentagonal symmetry, five limbs, rock-like shell, no visible eyes. Rocky breathes ammonia at 29 atmospheres, speaks in musical chords, and counts in base 6. Two species that couldn't be more different begin to understand each other.
Rocky Has Sonar
Passive echolocation and Fourier transform
Grace discovers Rocky doesn't see with light but with sound: passive echolocation. Aluminum is "transparent" to Rocky. Using Fourier analysis, Grace begins decoding the Eridians' musical language.
Building a Shared Language
Measuring mass in zero-g, exponential vocabulary, and loneliness
Grace and Rocky build shared vocabulary at exponential speed. Grace invents a method to measure mass without gravity, and Rocky reveals a devastating truth: his entire crew died from interstellar radiation.
The Black Panel and Neutrinos
Astrophage breeding farms, Majorana neutrinos, and radiation shielding
A flashback reveals how humanity produced tons of astrophages using simple solar panels in the Sahara. CERN discovers astrophages store energy as Majorana neutrinos, and their 96.415°C temperature isn't coincidence: it's pure quantum physics.
Erid
An alien planet, steam-powered muscles, and nukes to save Earth
Grace reconstructs Erid's biology: a super-Earth with 25× stronger magnetic field, where Eridians run on biological steam engines and mercury blood. On Earth, a desperate plan: detonate nuclear bombs under Antarctica to release methane.
Rocky Moves In
Dodecahedrons, astrophage cooling, and 689 years of life
Rocky moves to the Hail Mary in a xenonite dodecahedral ball with life support. Grace discovers Eridians live an average of 689 years, that Rocky has been at Tau Ceti for 46 years, and that together they can compensate for each other's weaknesses.
The Taumoeba
The organism that eats astrophages and can save the Sun
Grace and Rocky collect samples from Tau Ceti's atmosphere and discover something extraordinary: a second living species that feeds on astrophages. Taumoeba is the reason Tau Ceti hasn't gone dark. And if it can be adapted to Earth conditions, it can also save the Sun.
Solvents of Life
Why water and ammonia can support life, and why they don't mix
Grace and Rocky can't breathe the same air, touch the same materials, or share the same space without a hermetic seal. It's not by choice: their life chemistries are mutually destructive. Water and ammonia are the solvents of two civilizations that must collaborate without touching.
Directed Evolution
How to compress millions of years of evolution into weeks of lab work
The Taumoeba found at Tau Ceti is perfectly adapted to live in ammonia at 210°C. Useless for the Sun, where astrophages exist under very different conditions. Grace needs to create, in weeks, a Taumoeba variant capable of surviving in solar conditions. She will use biology's most powerful tool: directed evolution.
Orbital Mechanics
How to move through space without wasting fuel
Rocky needs to return to Erid to save his civilization. Grace needs to send the modified Taumoeba toward the Sun. Neither has enough fuel to do what they want by brute force. The solution lies in physics: orbital mechanics allows trajectory changes using the gravity of celestial bodies as a springboard, spending almost no fuel.
The Sacrifice and the Silence
Twelve years of delay, the speed of light, and the choice that defines Grace
Grace has the solution to the problem killing the Sun. But she's 12 light-years from Earth. Any message she sends will take 12 years to arrive. Waiting for a reply means another 12. Meanwhile, she must decide whether to attempt the impossible return journey or stay at Tau Ceti knowing she'll never see her planet again. The physics of communication at interstellar distances turns the most important solution in human history into an act of absolute faith.