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When a book like Project Hail Mary gets adapted for the screen, there’s always one big question: how faithful is it really?
Overall, this was a pretty faithful adaptation. A lot of the major plot points and emotional beats made it into the movie, but there are definitely some differences (some small and some pretty significant) that change how the story feels.
Here’s a breakdown of what stayed the same, what changed, and what I think worked (and didn’t).
What the Movie Got Right
A lot of what made the book special did translate well. The movie stayed pretty faithful overall, which is honestly impressive given how science-heavy the book is.
The ship design and the centrifuge explanation were really cool to actually see instead of just imagine. I think it might’ve worked a bit differently than what the book’s schematic showed, but I think it made more sense the way the movie showed it.
Also, I thought it was really smart for Rocky’s ship to also move with Grace’s ship while it was in centrifuge mode, so the tunnel would stay connected. I believe in the book, they couldn’t activate the centrifuge when Rocky’s ship was there, which is one reason Rocky moved into the Hail Mary so they could do science in the centrifuge mode. It made a lot of sense for the movie to show both ships spinning and was visually stunning.
Actually, all of the visuals were stunning, especially when Grace is in the Petrova line during the collection at Adrian. I would recommend seeing the movie just for the cinematic experience, even if it didn’t match the book closely.
The added room with screens showing Earth scenes wasn’t in the book, but it was a really nice touch. I think it made sense for the movie to include such a thing to highlight his homesickness since a lot of that was internal in the book.
The explosion scene being shown while they were awake made it way more impactful. Seeing it happen in the background hits harder than the book version, where Grace just feels his cottage shift and later finds out it moved off its foundation.
Also, Grace’s enclosure at the end was honestly better visually than in the book. The book ending made me a bit mad that he was affected so much by their gravity when I think the Eridians could definitely have done something about that, so I’m glad he had a better home in the movie.
Major Differences
There were some pretty noticeable changes in the movie, which some were understandable, but some I wish they had kept.
In the book, we never see Earth again, so we don’t get a scene at the end with Stratt on the boat receiving his messages and taumebas. The only indication in the book is that Earth’s sun isn’t dimming anymore, so seemingly the problem was solved and some people survived.
In the book, during the spinout on Adrian when Rocky leaves his enclosure to save Grace, Grace then saves Rocky by putting him back into his side of the ship to heal. Grace also creates something to shoot air at Rocky’s vents to remove the smoke, but it almost kills him. I do wish they put in the movie that Grace also saves Rocky, but I think it was a good call to cut the “almost killing him” part.
Also, it’s a small thing, but Grace never goes to Rocky’s ship in the book because of the gravity differences. I did like that they added that to the movie though, as it was another visually stunning scene, and I think everyone who read the book was curious what his ship would look like.
Movie Stratt and book Stratt are very different. The movie added a karaoke scene that wasn’t in the book, which does humanize Stratt, but in general, the movie Stratt is much more human and less imposing than in the book.
The movie doesn’t fully show how Stratt was basically in charge of every single government worldwide. I wish the movie had included the court room scene to show that Stratt couldn’t be held accountable for any of the things they did to succeed at the mission. Also in the book, she thought she’d be in jail or dead once the Hail Mary took off, so I didn’t think it was realistic she was on a ship and still in charge at the end of the movie.
The movie also didn’t include the major Earth-scale efforts like blowing up parts of Antarctica to release greenhouse gases to keep the planet warmer for longer or the terraforming of the Sahara to produce the astrophage fuel. With the book, the audience definitely understood the desperation of fighting against the world ending, but in the movie it didn’t feel as dire.
Missing Context & World-Building
This is where the book really shines, and where the movie had to simplify.
The movie never explains that only 1 in 7,000 people have the coma-resistant gene, which is why when the main and backup scientists die, Grace is literally one of the only other options. It also doesn’t get into Stratt knowing Grace has the gene and making sure he is at every single meeting on astrophage and other mission-critical meetings. He was her backup plan all along.
The beetles were pretty glossed over as well, and they didn’t include the Canadian scientist who invented them. The beetles were self-directing drones so nothing had to be programmed to get them back to Earth, and of course they’re named after the Beetles band members. In the movie, you only get one scene with the four of them taking off back to Earth with the band members names on them, so it’s something that could easily be missed if you hadn’t read the book.
Also, a lot of the deeper science explanations were cut (which makes sense for a movie), including the xenonite composites where Rocky is making a solid metal out of what should be a gas element, and Rocky discovering Grace can see light and stars. Since Rocky is an engineer and Grace is a scientist, there’s a lot of conversations in the book on cool gadgets and problem-solving details that just couldn’t be included in the movie.
Character & Storyline Changes
Some changes affected how the characters and relationships came across.
First, the movie didn’t go into much detail about the two scientists dating, which might confuse viewers who didn’t read the book as it didn’t seem obvious they were dating in the movie.
In the book, it makes it clear that the main and backup scientists are dating and therefore are together during the experiment that sets off the explosion. The movie just glosses over what experiment they were trying to do as well, and it’s very quick on explaining what went wrong so it was easy to miss. The book goes into more detail on both of those.
Also, when Rocky first sends something over, in the book Grace doesn’t think it’s a bomb or try to escape. He’s actually super curious and excited about meeting alien life, which feels more in line with his character. I understand it was funny to add the scene in the movie of Grace trying to flee and Rocky always showing up, but I did find it made Grace seem even more of a coward than he was in the book.
The Ending: Biggest Differences
The ending is where things diverge the most visually and emotionally.
In the movie, Grace should’ve been aged up more, closer to 50. In the book, because of the extra gravity, he already needs a cane and is aging more rapidly. Plus, it would take something like 15+ years for Earth’s sunlight to show on Erid that it’s no longer dimming, so he was much older in the book’s ending than it showed in the movie.
Also, his enclosure does not include water, and the way I was reading it, it didn’t have that much sunlight. From the book, he was basically in a house in a dome and all he could see out of it was darkness because Eridians didn’t have much sunlight make it to the planet’s surface.
The movie version is definitely more visually appealing, but the book version feels more isolating and realistic.
Final Thoughts
Overall, this was an amazing adaptation.
Yes, the movie simplifies a lot of the science and skips some deeper world-building, but that’s kind of unavoidable. What matters is that it keeps the heart of the story, and it really does.
Some changes I missed (like Grace saving Rocky), and some details I wish had more explanation, but the movie still delivers emotionally and visually in a big way.
If you’ve read the book, you’ll definitely notice the differences—but if you haven’t, the movie still stands strong on its own.
If you loved the movie but haven’t read the book yet, I highly recommend picking it up. The extra detail, science, and character moments add so much depth to the story.
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Read my Project Hail Mary book review
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