Here’s Why Grace Is the Only Astronaut Who Survived the Space Voyage in ‘Project Hail Mary'

Spoiler alert: The following contains spoilers for Project Hail Mary.

Ryan Gosling's been getting rave reviews for his work in Project Hail Mary, which was based on Andy Weir's book of the same name. If the author's name sounds familiar, as does the premise of the 2026 film, it's because Weir also wrote The Martian, which also sports a protagonist largely left to his own devices in outer space.

And with so much going on in the movie, viewers have been left with a few questions, like, how did the other astronauts on board with Ryland Grace (Gosling) die?

To make the journey through space, Ryland and the other astronauts aboard the vessel are put into a coma. Weir's book indicates that this process is necessary, as the three travelers on the ship are in a fairly cramped space, one described as smaller than the one shown on camera.

Thus, being in a coma minimizes the chances of astronauts slipping into psychotic episodes and succumbing to depression in the vacuum of space. However, this comatose state will only work on individuals who have specific gene markers, and there is only one in a million human beings who carry it, including Grace and the two other astronauts, Yao Li-Jie and Olesya Ilyukhina.

After Grace wakes up from his coma, he sees that Li-Jie and Ilyukhina's bodies have withered away, leaving him to fend for himself on board. Once at Tau Ceti, Grace encounters Rocky, an alien life form that has been hovering around the star for 46 years.

Like Grace, Rocky had crew members aboard his own trip to Tau Ceti for the same purpose: to save their respective home worlds. So the pair work together to discover why Tau Ceti, despite having the same Astrophage that Earth's sun has, isn't getting any dimmer.

Upon meeting each other, they then set out to nab a predator in space that will eradicate the Astrophage. These are the Taumoeba, which Grace and Rocky breed together to fight the world-ending threat in their respective solar systems.

The problem is, however, that these Taumoeba can move through Xenonite, which is what Rocky's ship is made from. These tiny predators get into Rocky's Astrophage supply and effectively destroy his ship. However, Grace arrives with a ship not made of Xenonite, and he's able to bring the Taumoeba to Rocky's home planet.

Eventually, Grace ends up on Erid (Rocky's world), where the Hail Mary ship has been fixed. Rocky tells Grace that he's allowed to return home if he wants, but in the film, he's hesitant about returning to Earth so quickly. In the book, there's less conflict about this decision: Grace is pretty sure he wants to stay on Erid.

He knows that the sun's Astrophage problem has been dealt with since it's burning brighter, but that doesn't mean Grace is in a rush to get back to the planet just yet. "Maybe I will go home someday. Maybe I'll find out for sure. But not right now. Right now, I've got work to do," he says.

Grace remains on Erid, and works to teach the young rock alien life forms out of an environment he can live in. And the Eridians make sure to make it as homely as possible for the human researcher. He's on a beach, crafted by the rocky alien people before he prepares a class discussion for young, inquiring Eridian minds.