Project Hail Mary opened in theaters last week, introducing the world to Rocky, the alien creature whose friendship with the main character, Ryland Grace, forms the heart of the story. Rocky quickly became a fan favorite of readers of the book, partly because of the extensive research and imagination put into the creature by the author, Andy Weir. In today’s video, I have Andy Weir join me to break down everything you could possibly want to know about Rocky, from his (not so) fictional planet to his crazy anatomy. It’s a masterclass in speculative biology that will amaze amaze amaze you.
TRANSCRIPT:
Project Hail Mary opened in theaters this weekend, based obviously on the book by Andy Weir, and if you’ve read the book, and I know a lot of you have, then you are more than familiar with the lovable alien character named Rocky.
Ever since the book came out in 2021, people have been falling in love with this character. It’s a fan favorite, there’s been all kinds of fan art devoted to it, people speculating on what it might look like, if you go online you can find tons of Rocky tattoos people have gotten, along with some of their favorite lines of his like “Amaze, amaze, amaze” and “Fist my bump”
If you know, you know.
But on top of just being a fun character, it’s also a truly alien creature, unlike anything we’ve ever really seen in sci-fi before.
It has five legs, no face, no eyes, talks through musical chords, and oh yeah… it’s made of rock. Hence, Rocky.
This isn’t just some guy in a weird mask, this is a truly bizarre creature that’s like nothing that evolved on Earth – which is exactly what I think a real alien would be like; like you probably wouldn’t even know what you were looking at.
But here’s the thing about Rocky, as weird as he is… He’s based on actual science. And the planet that he’s from is a real exoplanet that’s been found.
Andy Weir of course is also the author of The Martian, and he’s known for very science-based, hard sci-fi, so when it came time for him to create an alien, he did the science.
You might even say he scienced the shit out of it.
I actually found online his notes on how he created Rocky and oh my god dude, this is eleven pages of actual insanity.
He imagined every detail of its anatomy; its circulatory system, its nervous system, its digestion, its very cellular makeup, and it’s all based on how life might evolve from the conditions of a real exoplanet.
So to celebrate the release of this film, I thought why not take a serious deep dive into the character that stole the show – and everyone’s hearts along the way.
And because he’s a bit of a friend of the channel, I was able to elicit some help from the man himself…
So settle in because we went through his notes with a fine-toothed comb, examined the most popular Rocky designs, as well as the film’s design, and even got some one-of-a-kind graphics made so you can fully understand this one-of-a-kind alien.
I honestly think this might be the most thorough breakdown of Rocky to ever get put on YouTube. Like, most of this you can’t even find in the book or the movie. And Andy even shared with me some ideas that he’s never put out anywhere before.
So, if you’re a fan of Rocky, stick around, you’re going to get to know him better than ever before.
Obvious disclaimer here, there will be some mild spoilers for the book and the movie if you want to go in totally clean but I’ll leave out any major plot points that you can’t find in the trailers or anything like that.
But the basic backstory here is that in the book, scientists discover that the sun is dimming, as are a whole bunch of other stars in our galactic neighborhood, almost like a cosmic infection.
A molecular biologist named Ryland Grace, played by Ryan Gosling in the movie, figures out that it actually is an infection, an infection of a space microbe that he named astrophage that’s eating away at the sun’s fuel source.
This is obviously a problem because the dimming sun is going to lead to a frozen Earth if nothing is done about it.
The only clue they have for how to solve it is found in another star system called Tau Ceti, which, despite being right in the middle of all these other infected stars, it’s not dimming. It seems to be immune to this infection.
So if they can figure out why this star is surviving, maybe they have a chance to save our own sun, and avoid the extinction of all life on Earth.
With that in mind, they hatch a plan – a hail mary if you will – to send a ship to Tau Ceti and figure out its secret.
Since Ryland Grace was the one who figured out astrophage in the first place, he kinda gets drafted to go on this mission.
And this is all backstory, where the story starts, Grace wakes up from deep hibernation in orbit around Tau Ceti. There’s just two problems, one, he has profound amnesia and has to reclaim his memories and figure out who he is and why he’s there, and two, he finds that his crewmates passed away while in hibernation
Alone, in deep space, with little hope for survival, much less any chance of success, Grace works against the odds to solve the problem. And that is when Rocky shows up.
He’s there for the same reason, their star is also dying, and he’s there trying to save his planet. Also like Grace, Rocky’s fellow crew members expired along the way.
Thus begins perhaps the strangest bromance in history as the two bridge their cultural and physical gaps and work together to solve the problem, and save their respective worlds.
In Rocky’s case, the world he’s trying to save is 40 Eridani A.
40 Eridani is a star system in the Eridanus constellation, and it’s actually 3 stars – it’s a triple star system.
40 Eridani A is the main star, which is orbited by the twin stars 40 Eridani B and C.
And in 2018, a paper was released by the Dharma Planet Survey that reported regular dimming of 40 Eridani A, suggesting there may be a planet transiting it, really close to the star. The name of this planet is 40 Eridani A b. Because planet nomenclature is weird.
In the book and the movie, they just call the planet Erid for simplicity so if you’ll indulge me, I’ll do the same. Because I, too, am simplicity.
They did the math and found that it had 8.47 Earth masses, making its radius a little less than twice the size of Earth, so it’s a big boy. It has an orbital period of 42.245 Earth days at an eccentricity of .04, but the wild thing about this planet is that its semimajor axis, basically the average distance from the star, is .224 au. If you don’t know, one AU is the distance from the Earth to the sun, so it’s basically 1/5 the distance from its star as we are from the sun.
For context, Mercury is roughly .39 au, so this planet that’s twice the size of Earth is orbiting its star closer than Mercury is.
I should point out that there have been some papers – one of them was in 2024 – that suggested that this planet may, in fact, not exist. That the dimming that was recorded was from stellar fluctuations. But for the purposes of all this, let’s just Shh….
Also, I didn’t know this when I talked to Andy, but in Star Trek lore, 40 Eridani is where the planet Vulcan is. I don’t know if this was a nod on his part to Star Trek, but in theory, Spock and Rocky might be neighbors.
But those are the parameters of this planet, this is what we know. From there, he started worldbuilding. Literally.
Now, before we continue with the worldbuilding stuff, I need to take a quick detour because it explains the rest of the decisions that were made around this planet, which affect how Rocky evolved, so if you’ll give me a second, I need to talk about panspermia.
I’ve covered this here before but if you don’t know, panspermia is the idea that life was seeded here on Earth from somewhere else in the universe, like a bacteria that survived on an asteroid, something like that. And, expanding out, life may have spread throughout the galaxy in that way.
Like the astrophage I talked about earlier, that’s basically panspermia.
So he wanted to keep that as part of the book, the idea that life on Earth and life on Erid came from the same panspermia event. Because he thought that he needed something to explain why there was so much life is in this one area of the galaxy He thought that it made more sense for all of that life to come from the same place than for three different star systems so close to each other to develop life independently.
Pressure changes everything.
But to keep that pressure, you have to have something to keep the solar wind from blasting the atmosphere away, and he came up with two solutions for that, one is a super strong magnetic field, which is usually created by a dynamo in the planet’s core. So he made the planet spin really, really fast. Basically a day on Erid is only 5 hours. As for the second solution…
So if you’re keeping score, we’ve got a planet roughly twice the size of Earth, a rocky planet with a very thick ammonia atmosphere and super hot because it’s so close to its star. Surface temperature’s around 210 degrees but you’ve got liquid water because of the high pressure.
So now he’s gotta figure out what kind of life would evolve on a planet like this. There’s just one problem…
So in the ocean analogy, Eridians would be like bottom feeders, in fact the entire terrestrial ecosystem would be similar to the ecosystem on the ocean floor.
And if the idea of bottom-dwelling ocean creatures makes you think of things like crabs and starfish… Well, you’re onto something.
Eridians are kind-of like a cross between a crab and a starfish. They have a hard exoskeleton with legs that connect to a thorax like crabs, but they have radial symmetry with 5 legs like a starfish.
They’re fairly small, compared to us. They average about 50cm tall (a little over 1 1/2 feet tall) when on all fives but can stretch upward to reach 1.3 meters high (4 1/4 feet). Imagine a crab the size of a border collie.
Which by the way, I have a theory that that’s why I think people find Rocky so endearing is he’s kinda like a dog. A dog that’s maybe smarter than you.
I mean he’s got a fun personality that’s easy to fall in love with but it is kinda like the personality of a dog. He’s friendly and helpful, and sometimes just kinda silly. But he’s also loyal and brave and empathetic.
I mean who wouldn’t want to have a conversation with their dog and take them on adventures and solve science puzzles together?
Their legs are joined at the thorax with a ball and socket joint like our shoulders, which allow them to reach in all directions, with a hinge joint like our knees and elbows halfway down.
And they have three stony fingers on each hand that they use both as feet and hands, they can walk on them or they can manipulate objects with them, in fact, he describes them as “pentadextrous” meaning they can use all five hands to do whatever.
Though they usually stand on three feet while using two to grab and do things with.
And because they’re radially symmetrical, they have no “front” or “back” and can travel in any direction without needing to turn around or face a certain direction.
They also don’t need to face any certain direction to see because they don’t have eyes.
So yeah they basically see in all directions at the same time by echolocating off of surfaces, kinda like lidar.
And by the way, in a high-pressure ammonia environment, sound actually travels faster than here on Earth so that sense would be heightened compared to, say what a bat can do.
So pretty much all their sensory input is through this echolocation, they don’t really have a sense of touch because their exoskeleton is made of rock.
So yeah Eridians don’t breathe. They’re basically just like a self-contained ecosystem
Just like you and I are made up of cells, Eridians are also made up of cells, but their cells are kinda like a whole bunch of different species working together to transfer energy back and forth, to the point that they don’t have the same genetic material.
And while these worker cells travel all over the body to repair and maintain and build, they live mostly in an area called the Colony.
The colony sits inside the carapace, and this is where the worker cells hang out and reproduce and repair each other, and the colony is able to close itself off completely from the rest of the body in case of injury or infection.
It’s also where the body’s most vital organs reside, because they can be shut off and protected. Vital organs like, say, the brain.
And if all of this isn’t weird enough for you, it’s about to be. Because we gotta talk about that brain.
Because Rocky’s brain… is made of crystal.
This is why Rocky was such a genius engineer, his brain is basically a computer. I imagine that they just burn information like we do on a CD or a hard drive. Once it’s in there, it’s in there for good.
And if I may opine for a second, I think this is where the book really shines, in those little personality and cultural differences between Grace and Rocky.
They have different intelligences but they find a way to complement each other and achieve what neither of them could do alone. All while bridging the widest cultural gaps you can imagine.
And I don’t think anything illustrates that more than the difference in how they eat. Because it is very different.
Humans have this digestive tract that starts with our mouth, where we chew things up, and it passes down through the body, winding and weaving around, squeezing all the nutrients out of the food, and the waste gets yeeted out the other end. It’s one long continuous tube. You’re basically a worm that grew a human around itself.
Eridians, as I was saying before, they’re completely sealed off from the outside. There is no tube. But they still need to consume energy, so they have one orifice that’s both the in and out hole.
Basically when they eat, worker cells open up a seam in the bottom of their carapace. This allows them to open the hatch and expel the previous food that had been in there. They then put in the new food and replace the hatch, and worker cells seal up the orifice again.
Now a couple of little things about this process is since they don’t have mouths and teeth to chew up this food, they have to do it with their hands. Before they eat, and they’re predators, so they usually eat other animals, they first process the animal by going through and pulling out all the non-useful parts and only keeping the useful parts before stuffing it inside themselves.
So this activity of tearing the food apart and separating it, that’s like chewing to them. And it creates a pleasurable sensation for them.
The other thing is because this is the only time they expose their insides to the air, they have to sanitize the food after they put it in their stomach, which they do by raising the temperature in the orifice really high. This, of course, takes a lot of their energy and it can put them in a bit of a sleepy state for a while after they eat. They have literal food comas.
But to them, eating and pooping is kinda the same activity. And there’s a really great bit in the book where Rocky needs to eat something and Grace offers to join him an Rocky’s like, “What’s wrong with you?”
Yeah… we talked about shit for like 30 more minutes…
Let’s talk about Rocky’s circulatory system instead.
They actually have two circulatory systems, and it works basically like a steam engine.
The first system is called the Ambient Circulatory System, or ACS, this keeps the blood at the ambient temperature of their environment, 210 degrees celsius – which, again, is below the boiling point in their high pressure atmosphere.
The second system is called the Hot Circulatory System, or the HCS, which is kept slightly higher, just above the boiling point.
Now if you’re wondering how they have blood that’s above the boiling point of water, it’s because their blood is made of mercury.
Weird enough yet? Hold on.
Their blood is pumped by 5 hearts, situated above the leg joints in the carapace, and they pump blood down into the legs where the capillaries from the two different systems come into contact with each other, and that’s where the magic happens in the muscles.
They’re a steam engine.
All of this introduces one tiny wrinkle, which is, how do the water-based worker cells maintain and repair the hot circulatory system if it’s above the boiling point of water?
And this is another fun character bit from the book, when Grace sleeps, Rocky insists on watching over him, and he feels weird sleeping without Grace there. It becomes a little bonding thing between them.
So, again, plot points, character traits, entire cultural norms of this alien creature are all tied back to the physics of his anatomy. And the physics of his anatomy all ties back to the environmental conditions of his planet.
I know I’m probably blowing smoke here but as a writer, I’m fascinated by this process he has. These 11 pages of insanity, that he spent God knows how much time thinking about and ruminating on, 90% of which is never even revealed in the book or the movie, is the bedrock on which he built one layer after another to ultimately form this story and their character arcs.
This is why the nerds love this book so much!
A few more things to talk about here, one of the big ones is communication, how Rocky talks.
This is a big plot point in the story, Grace has to figure out how to communicate with Rocky. Now Rocky doesn’t have that much trouble understanding Grace because again, he has this computer brain, he just needs to hear a word one time to know what it means forever.
Grace, on the other hand, needs a computer to figure out what Rocky is saying. Especially because to a human, Rocky’s language is just kinda random sounds.
It’s a tonal language. But not just tonal, multi-tonal.
A tonal language is one where the tone of a word – or the pitch if that works better – changes the meaning of the word.
So like if I were to say pen, and then I said (high tone) pen, those would mean two different things in a tonal language.
And there are a lot of variations of tonal languages around the world, especially in Southeast Asia, but also the Navajo language is tonal, there are several tonal languages in Africa and even some Scandinavian languages use pitch to change the meaning of words.
Even in English, the inflection of a word can change its meaning entirely. For example…
But Rocky has a multi-tonal language, he can combine multiple tones together to create different meanings.
Imagine what their social media must be like.
I guess it would be blissfully nonexistent since they don’t have computers…
Speaking of computers, the last thing I’ll touch on here is their technology, because they don’t have computers. Also… they don’t have fire.
Xenonite is a theoretical material made from Xenon that’s only possible in their high temperature/high pressure environment, and it has some incredible properties that Eridians have figured out how to manipulate to make pretty much everything.
Like you know we’re always hearing about the potential of nanofibers to create materials of incredible strength, this is their version of that, and they can do all kinds of crazy things with it.
Everything from Rocky’s ship, named the Blip-A, to the little models he makes for Grace when they first meet – that was actually their first form of communication, was Rocky just putting on a puppet show with these little models he makes out of Xenonite.
Xenonite is also what allows Rocky to travel into Grace’s ship, the Hail Mary, he creates a little bubble out of Xenonite that maintains his air pressure. Because obviously if he were to enter Grace’s air pressure, the water in his blood would immediately boil and he would die.
Which is also kind-of another heartbreaking part of the story, they form this beautiful connection, but they can never touch each other. If Grace ever shook Rocky’s hand, it would probably melt Grace’s hand.
So anyway, Xenonite has some amazing properties that made their entire space program possible.
That’s another interesting thing about Rocky and the Eridians, on one hand they have amazing technology far beyond ours, but in others, they lag behind.
Since they have no eyes, they are completely unaware of electromagnetic radiation, which is essentially what light is. Also the fact that they have such a strong magnetic field on their planet.
So they had to discover radiation once they got into space, and that became a problem to solve because they had no defenses against radiation.
The way they solved for this in space travel was they put a strong magnetic field around their ships.
Another thing that becomes a plot point is they don’t understand relativity, so it’s a cool mix of them being super advanced in some ways and behind in other ways. And again, it’s that cooperation between Rocky and Grace, each one filling in the gaps of the other that forms the heart of the book.
So as I’m recording this, the movie hasn’t come out yet, so I haven’t seen it – I will have seen it by the time this video gets released, I may give my thoughts on my second channel.
But I’m super excited to see this movie. It might be the first movie I’ve been genuinely excited about in a long time. We did talk a little bit about the movie, especially how they brought Rocky to life.
Anyway, I’m gonna wrap up this video before it gets longer than the movie – I promise I’m not getting paid by Amazon to promote it, I just really wanted to take a deep dive into Rocky because I loved the speculative biology involved.
You know, there’s so much variety of life on Earth but it mostly operates in similar ways, and that can kind-of put us in a box in terms of thinking of how life could evolve in other places.
We like to focus on Earth-like planets because that’s the kind of biology we know and understand – and that makes sense to do that – but there’s literally a whole universe of possibilities out there and it’s really cool to explore those possibilities.
Also it’s always been a slight annoyance of mine when science fiction shows people just hopping from one planet to another, breathing just fine like every planet has the exact same air pressure and atmospheric composition – they just totally ignore that problem.
But this story doesn’t ignore that problem, in fact it leans into it, it uses it to create a compelling narrative and interesting characters – and I think that’s why people love it so much, and why people love Andy’s writing in general, he uses the science to create drama and emotional stakes.
And on a personal note, I first met Andy when I interviewed him for a video in 2019, and ever since then he has been a huge supporter of the channel and I consider him a friend, and I would just like to thank him for all his support over the years, it means a lot to me.
So, if you haven’t read the book, read the book, if you haven’t seen the movie, go see the movie, and if you have done either, drop a comment down below, what did you think of the movie, what’s your favorite part of the book?
Do you have a Rocky tattoo? share it and tag me on Instagram.
And tell me if the book inspired you in any way. I saw in an interview with Ryan Gosling, he said his favorite thing about Andy’s books is that they treat the future as just a problem to solve. And that’s a hopeful way to look at things. And I like that, I think we all need a little bit of that right now.
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