Project Hail Marys ending makes one big change from the book. Heres why.
Like any book-to-film adaptation, Project Hail Mary makes some changes to its source material.
In most cases, Project Hail Mary's changes look like removing elements of Andy Weir's novel in order to streamline the film. For example, in the book, a key part of finding astronauts for the Hail Mary mission is determining whether they have a very rare coma resistance gene, all of which is missing from the movie. Another omission? A plan to power Astrophage production by covering the Sahara Desert in solar panels.
However, Project Hail Mary does make one addition in its final minutes that isn't in the book.
The film ends very much like Weir's novel, with biologist Ryland Grace (Ryan Gosling) living not on Earth, but on alien Rocky's (voiced by puppeteer James Ortiz) home planet of Erid. He's sent the Hail Mary's beetle probes back to Earth with instructions on how to breed the Astrophage-eating Taumoeba and save the sun. In the book, after Grace has spent years on Erid, we learn that the sun's luminosity has been restored, meaning Grace's research made it to Earth and humanity is saved.
However, we never actually see what that process looks like in Weir's book. In fact, we never return to Earth, as we're in Grace's mind the whole time.
The movie, on the other hand, does bring us back to Earth as the film winds down. It shows us its now-frozen oceans, a result of global cooling due to the sun's dimming. It also shows us what's happened to Stratt in the years since the Hail Mary launched.
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Stratt's fate remains a mystery in the novel, although she believes that she'll eventually wind up in prison due to the extreme actions she took to get the Hail Mary off the ground. (The Sahara Desert plan, for example, proves an environmentally destructive resource drain, although it gets the job done.) The film takes a more optimistic approach, showing that Stratt is still alive and has received the beetles. Now, she's ready to start work on the next phase of Project Hail Mary.
"Quite honestly, I love writing Stratt," screenwriter Drew Goddard told Mashable while discussing Stratt's ending. "This movie is about three characters, really. It's a triangle between three characters, and we need to give her her moment."
Thus, Stratt's epilogue was born, granting us a hopeful glimpse into humanity's recovery effort.
Goddard continued: "That's what great about movies. You can cut away, whereas the book stayed with Grace. Once I put [the scene] in, no one questioned it. I was really grateful that they let us do it, because I thought it was really important to see her."