The tiny rock-like and somewhat spidery alien that shares the screen with Gosling’s Ryland Grace, Rocky has quickly become a fan-favorite thanks to his mannerisms and hilarious gags in the film. Those who read Weir’s book, first published back in 2021, have known how hilarious Rocky has been for some time, which makes his burst in popularity for non-readers even more enjoyable. That said, there are major elements about Rocky that aren’t revealed at all in the Project Hail Mary movie that can only be found in the pages of the Project Hail Mary book. Some funny, some unique, and others devastating, these are our favorite Rocky facts not present in the Project Hail Mary film. Spoilers will follow.
10) How Rocky Measures Time
There are a lot of clear distinctions between Rocky as an Eridian and Ryland Grace as a human, and one of the biggest is their measurements of time. One scene in the film hints at this when the two share their respective versions of a clock with each other. What the scene in the film doesn’t make clear that the Project Hail Mary book illuminates is the specifics of Eridian time vs Earth time. The Project Hail Mary book goes on to reveal that 1 Eridian second is equal to 2.366 Earth seconds, showing how differently Rocky and Grace view time. We’ll get into this even more later.
9) Eridian Science Is Lacking in Some Places
One of the most unique quirks about Rocky and the Eridians is that their science methodology is totally different from that of humans. It’s one of the reasons he’s such a great partner for Grace; their scientific focus is on different ideas so they have a nice venn diagram of expertise. This becomes clear not only from how he can make solid matter from the noble gas Xenon, but also when Grace realizes that the Eridians have no concept of major elements of physics like relativity. As a result, Rocky was surprised to arrive at Tau Ceti in three years when the Eridians believed it would take over six and a half.
Grace eventually explains the concept to Rocky in the book that time and space change depending on speed and gravity, meaning Erid experienced more years in the time Rocky was gone than he did, but he is “dumbfounded” by it at first. On the flipside, Grace is astonished that an entire planet of scientific minds created a ship that could travel to Tau Ceti simply by making assumptions.
8) How Sensitive Eridian Hearing Is
It’s clearly referenced throughout Project Hail Mary that Rocky and other Eridians largely experience the world through sound, as they have no eyes. A detail that the book gets into more than the film is just how sensitive their sense of hearing really is. What Project Hail Mary, the book, makes clear is that Eridians’ sense of hearing is equivalent to our own sense of touch, with receptors across their bodies, making their entire body like a giant microphone.
7) The Size of Erid
Even though there is a scene set on Erid at the end of Project Hail Mary, just like the book, details about the planet itself aren’t really revealed in the film. Erid is over 8.5 times the size of Earth and twice its diameter, and is also 1/5 as close to its sun as Earth is to our sun. As a result, one “year” on Erid is actually just 42 days on Earth, while an Erid “Day” is only 5.1 hours. All of that combines into a major distinction about the planet: it has double the gravity of Earth, something not made entirely clear by Grace’s presence on the planet in the final scene (though the Erid scientists may have fixed it for his habitat).
6) The Inside of Rocky’s Body
Rocky’s physiology isn’t really discussed in the Project Hail Mary film, but it comes up in the book. Grace learns that Rocky’s body is made almost entirely of oxidized minerals with very few actual biological materials. Inside his carapace, Rocky’s bones are structured like honeycombs, his blood is liquid mercury, and his circulatory system exists by fluctuating the temperature of his blood. In the end, Grace simplifies it to say that Eridians are “steam-powered.” Rocky goes on to reveal there’s only one opening in the body of Eridians, used exclusively to eat or lay an egg.
5) Rocky Is Very, Very Hot
As noted, Eridians have liquid mercury for blood, heating up and cooling down parts of their body in order to move about. Rocky even reveals at one point in the book that the way Eridians fight disease is by heating up their blood and concentrating it in the affected part of their body, killing the disease with pure temperature. All that in mind, one of the things that’s not really made clear in the movie is that Rocky is very, very hot. Grace makes this clear by revealing that by simply entering a room on the Hail Mary, Rocky makes the entire space warmer.
4) How Much Rocky Weighs
Rocky’s size in comparison to Grace is clear from their first encounter, but what’s not really obvious in the Project Hail Mary movie is how heavy he is. Given he’s made of rocks and has such a heavy interior, it shouldn’t surprise fans to learn that Rocky is…cumbersome. In the Project Hail Mary book, Rocky reveals that he weighs 168 kilograms or 370 pounds, and on Erid, Rocky weighs over 800 pounds due to its extra gravity. Grace is only able to lift Rocky and his ball in the book due to the lack of gravity upon his entry into the ship, prompting him to ask about Rocky’s mass. Rocky is stunned to learn that Grace’s mass is less than half his own.
3) How Long Rocky’s Been Waiting
One of the saddest details about Project Hail Mary‘s story is that Rocky’s entire crew died on their trip to Tau Ceti; as a result, he’s the only surviving crewmember of his ship (the “Blip-A”). What isn’t revealed in the Project Hail Mary movie is how long he has been sitting at the star waiting for either rescue or additional help from Erid, revealed to be 46 years, Earth years that is. Yes, Rocky has been sitting at Tau Ceti for longer than Ryland Grace has even been alive.
2) Why Rocky Needs to Watch/Be Watched While Sleeping
One of the funniest encounters in Project Hail Mary, the book and the movie, is that Rocky insists on both watching Grace while he sleeps and also being watched by Grace while he sleeps. In the film, though, it’s never revealed WHY this is the case. The pages of Project Hail Mary reveal that Eridians don’t “sleep” in the same way that humans do; instead, their brain has no actual function while sleeping, and their bodies are actually paralyzed, which is why they need another present to “watch” them sleep, to make sure nothing happens to them. In truth, it’s a practice that probably happened early in the evolution of their species and may not actually be needed anymore, but has become a custom. Eridians also have a range of how much sleep they may need, sleeping for a minimum of three hours and a maximum of 12 hours, and they only require sleep every 86 hours or so.
1) How Old Rocky Is
While detailing how long he has been on the Blip-A, Rocky goes on to reveal his age, confirming that he’s some 291 Earth years old, born around the same time as the first president of the United States, George Washington. Lest that seem like a lot, Rocky hasn’t even reached half of his full lifespan, revealing to Grace that the average Eridian can live up to 689 Earth years.
To put the time into perspective even further, Rocky says that he still has about 70 Earth years left before things even get that bad on Erid with the problems caused by Astrophage. This is due to the immense heat in the atmosphere of the planet, making it harder for it to have the same effects on it from its sun.
