Save the world. One mistake at a time.
Why it is hard sci-fi
The premise is a hard astrobiology problem. Astrophage, a microorganism that stores stellar energy and uses it as photon-rocket thrust to migrate between stars, is dimming the Sun by absorbing its output. Earth has decades, not centuries. A school science teacher with an old astrophage-related paper is conscripted onto the Hail Mary, a one-way mission to Tau Ceti, the only nearby star astrophage cannot infect. The film treats every step as engineering. Cryosleep with metabolic loading to survive an interstellar transit, a centrifugal living ring for spin gravity, delta-v budgets that leave no margin for return, and a beam-line propulsion stage that doubles as a hazard the layout of every compartment is built around. The protagonist solves problems with arithmetic on a tablet, and the film shows the work.
Science inside it
Relativistic time dilation across a twelve-light-year transit, the Petrova line as the visible signature of astrophage migration between bodies, photon-rocket propulsion as the organisms actual mechanism, and the stoichiometry of carbon dioxide and methane in a closed life-support loop. Spectroscopy is treated as a working diagnostic. The film commits to a fixed rule for astrophage and lets the entire mission flow from it. The science of the trip itself is conventional. Insertion, attitude control, reaction mass, and the unavoidable fact that a propulsion stage capable of relativistic speeds is itself a weapon-grade emission source.
Spoiler alert
The mid-mission discovery is xenocontact. Grace meets Rocky, a silicon-and-tantalum-shelled member of an Eridani species whose homeworld is dying for the same reason. The Eridani atmosphere is hot ammonia at high pressure, and Rocky communicates with drum-equivalent organs and runs on a different chemistry. The film handles this with a working language-acquisition arc and an interface compartment that splits the two atmospheres at the membrane. The cure to astrophage is Taumoeba, a predator microbe from Adrian, a moon at Tau Ceti. Grace gives up his return trajectory to ferry Taumoeba to Eridani and survives because Rocky takes him in. The final image of an old man teaching alien children is earned by the physics that put him there.