5 burning Project Hail Mary questions answered by Andy Weir’s book

Phil Lord and Christopher Miller’s Project Hail Mary is highly faithful to Andy Weir’s 2021 science fiction book of the same name. Lord and Miller hit all the highlights of Weir’s story about a desperate mission to Tau Ceti to save Earth’s sun, but they do trim away some of the author’s explanations about the mission and the apocalyptic threat. So if you still have some questions after watching, here are the answers Weir wrote.

[Ed. note: This article contains major spoilers for both versions of Project Hail Mary]

1

Where did astrophage come from?

The mission known as Project Hail Mary was created to deal with the threat of a microscopic organism dubbed astrophage that’s feeding on the Sun and causing it to dim, which will cool the planet and cause the extinction of all life on Earth. Scientists observe that all of the nearby stars are similarly dimming, except for Tau Ceti. They decide to send a spacecraft there to find out why.

Weir explains in his book that astrophage evolved in the Tau Ceti system where a local predator, dubbed taumoeba, kept its population in check and prevented it from dimming the star. Astrophage is compared to cane toads, a species from South America that devastated Australia’s ecosystem when they were accidentally introduced there. The key to saving the Sun was harvesting taumoeba and bringing it to Venus, where it would devour migrating astrophage and keep it from feeding on the Sun.

Tau Ceti is even more important in Weir’s world. Space is enormous, and he wanted an excuse to have three planets with life within a relatively small area of the Milky Way. So he called on the Panspermia theory, which posits that life on Earth evolved from microorganisms that came from somewhere else. Weir’s book explains that life on both Earth and the planet Erid started with a progenitor of astrophage originating on Adrian, a planet orbiting Tau Ceti. That’s why humans, Erideans, and astrophage all have cells powered by mitochondria.

2

Why is a school teacher in space?

When science teacher turned astronaut Ryland Grace (Ryan Reynolds) first learns to communicate with the alien astronaut he names Rocky (James Ortiz), one of Rocky’s first questions is, “Why is a school teacher in space?” It’s a good question! Grace secured a leadership spot on the team by figuring out how to breed astrophage to turn it into fuel. When the mission’s primary and alternate science specialists are killed in an explosion, Project Hail Mary lead Eva Stratt (Sandra Hüller) forces Grace to go to Tau Ceti because delaying the mission to find someone else would result in a lot more death as the cooling got worse.

The book provides a different explanation on why Grace was the only viable alternative for the dead scientists. The three astronauts on the Hail Mary are put into comas for the 13-year trip to Tau Ceti because psychologists say they’d otherwise go insane and kill each other. But being in a coma for that long is extremely risky. In the book, scientists discover a gene that makes a tiny percentage of humans more likely to survive the process. All of the astronauts chosen for the mission have it, and so does Grace, but none of the other scientists working on the project do. That makes him the only viable replacement despite his fears.

3

Does Erid have water?

Grace only started teaching after ruining his reputation as a microbiologist by writing a paper positing that water isn’t necessary for life. Project Hail Mary lead Eva Stratt recruits Grace because she thinks a microorganism that can survive on the surface of the sun could prove his theory correct, though Grace is disappointed to learn that astrophage is mostly water. Weir’s book makes it clear that Grace was right. Rocky’s species evolved on a planet without water. The seaside home the Eridians devise for Grace is an invention of the film.

4

Why did Grace lose his memory?

Image: Amazon MGM via Polygon

Grace wakes up from his coma with retrograde amnesia, and he slowly remembers why he was sent on the mission and that he really didn’t want to go. The movie writes the memory loss off as a symptom of the coma, and the book initially does as well. But the book eventually reveals that Stratt gave Grace a memory-loss drug when she put him in a coma. She correctly assumed that by the time Grace remembered she’d betrayed him, he’d be too excited by the science of saving the Earth to care how he got there.

5

What happens on Earth?

Both the film and Weir’s book end with Grace living on Erid, teaching young Eridians science, and contemplating returning to Earth. But the book actually ends 16 years after Grace and Rocky visited Tau Ceti, with Grace learning that his mission was a success and the Sun has returned to its original luminescence. While many people likely died on Earth as the temperature cooled, the book also explains one big way humanity coped with the sun’s decline: Stratt’s team nukes Antarctica to release trapped water vapor and methane into the atmosphere and increase the greenhouse effect to heat Earth.