Ryland Grace drifts in and out of wakefulness to a robot (consisting mostly of a set of arms) assessing his basic cognitive functions and removing a number of tubes attached to his body. He doesn’t know where he is, why he’s there or what his own name is.
As he attempts to get out of bed, a catheter rips out of his penis, leaving a small streak of blood. It prompts him to flash back to a memory of himself having breakfast at a diner.
In the flash back, he checks his email via his phone. He reads an astronomy mailing list email sent from Dr. Irina Petrova asking for ideas and suggestions about possible causes of an astronomical anomaly — a nebulae in earth’s solar system emitting a thin, curved line of infrared light that extends from the Sun to Venus — she’s identified in her research.
In present day, Ryland recalls that he lives in San Francisco. He also sees that next to him currently are two desiccated dead bodies, one man and a woman, who appear to have been dead for quite some time.
The robot-arms instruct him to eat a tube of brown sludge labeled “Meal 1”, which, as it turns out, looks disgusting and tastes fantastic. The room he’s in has no door, only a ladder leading up to a laboratory. The robot-arms also continually ask him his name, refusing to let him out of the area until he’s able to recall it.
Noting how everything feels a little off, Ryland quickly comes up with a makeshift experiment to test the gravitational force in the room. It’s 15 m/s², whereas the Earth’s is 9.8 m/s². From that, Ryland realizes he may not be on Earth.
Ryland wonders if he’s perhaps on a centrifuge on Earth (which could simulate gravity), but after taking some measurements with a makeshift pendulum, he concludes that’s not the case.
Then, in another flashback, Ryland thinks about a close friend of his, Marissa. They met 20 years ago in grad school, and now they have dinner at the same place every Thursday night. She works for the Department of Energy (“DOE”).
In the flashback, she brings up the Petrova line (the astronomical anomaly mentioned in the previous flashback), which she says the President of the United States is about make an announcement about. She indicates that it’s linked to news about the Amaterasu, a Japanese solar probe. The probe has detected that the sun’s output is exponentially decreasing, which is worrisome since it indicates that the sun is dying.
In present day, Ryland starts to remember bits and pieces about the so-called “Petrova problem”. He wonders if his job here was to work on that. And as he starts to remember the personalities of the two deceased people, he gets emotional. He remembers that he and his crewmates and were being held here on this spaceship in suspended animation. Not something fancy, but rather a medically induced coma where they required constant care, likely from the robot-arms. Ryland reasons that since comas are dangerous, that’s likely why the other two died and his brain is out of sorts.
In another flashback, Ryland recalls watching the live broadcast of the most watched event in television history, reporting of the initial results of Project ArcLight. ArcLight was an unmanned probe that was sent to Venus as part of a multi-national collaboration a year after the Japan Aerospace Exploration Agency (JAXA) had made their announcement about the sun possibly dying. ArcLight was meant to gather data and samples about the Petrova line. In the live broadcast, images of moving dots indicated that it might be proof of a microscopic extraterrestrial life form.
In present day, the ship’s computer informs Ryland that the ship is off-course. (Ryland also figures out that it’s able to respond to his commands and answer his questions.) However, Ryland is still not able to access the main parts of the ship where the navigational controls likely are, since he still can’t remember his name. As he struggles to recall, it occurs to him that he works as a teacher.
Ryland thinks back to the time after the announcement about the Petrova line. Despite the possibly apocalyptic nature of that discovery, life had continued as usual for most people. Ryland, too, had continued teaching science to his middle-schoolers … until the day Eva Stratt from the Petrova Taskforce, an international joint-effort, had come looking to talk to him about a paper he once authored.
Before this, Ryland had been working in academia and had spent years arguing that life could exist without water. In the paper she references, Ryland had berated other scientists for believing otherwise, which resulted in him getting his funding cut off and him losing his job.
That day, Eva tells Ryland that they want him to come look at the ArcLight samples when they arrive. He initially refuses, but he is soon escorted by the FBI to Eva’s lab. Eva says that they believe the microscopic alien life forms are effectively “eating” the sun, which is why it’s dying. She reassures him that other scientists will be inspecting the samples as well, but Ryland is being given priority because it’s likely these tiny, sun-dwelling creatures are an anhydrous (non water-based) life form.
In present day, Ryland is able to access the rest of the ship after having finally remembered his own name. He finds the pilot seat and sees that he has a very clear view of the sun.
As he scans the various navigational screens, one readout shows that the ship is trying to auto-correct it’s course, and it shows his current and predicted velocity. Ryland notes that his velocity is fast enough to escape the sun’s orbit. This means he’s either 1) going to go careening into the sun or 2) going away from it or going to bypass it, but either way headed into deep space with no hope of returning (because we know he’s not in orbit).
As for whether he’s headed it towards or away from the sun, Ryland figures he’ll know soon enough if it looks like the sun seems to be getting smaller or larger from his point of view. From the screens, he sees that his ship is called Hail Mary and his crewmates were Chinese and Russian.
Ryland then recalls the arrival of the ArcLight samples. In the flashback, He’s outfitted with a hazmat suit and placed in a vacuum-sealed lab filled with argon to work with the samples. After a few hours, his first observations confirm that these are tiny life forms. They have extremely high heat resistance and absorb x-rays. They also give off a tiny amount of infrared light (which is a anomaly Petrova originally identified), but only when they are in motion.
Moreover, Ryland believes the light is the mechanism that gives them the momentum to move around. He also says that these tiny dots have incredible amounts of energy stored up relative to their size, at levels unseen anywhere else in nature. In effect, these tiny dots consume and store energy, which they then use as a propulsive force for movement. The Petrova line is the light they emit reflecting off nearby space dust.
Essentially, the dots are single-celled aliens. He equates them to “space algae” and calls them “Astrophage“, which means they eat stars (from the Greek word astér/”star” and the latin suffix -phage/”to eat”).
Then, in present day, Ryland notices that the sunspots on the sun are moving at a rate faster than he’d expect. After some calculations, Ryland realizes he’s not looking at the sun, but rather a different star in a different solar system.
Ryland panics slightly upon his realization that he’s in another solar system.
He takes another look at his screens and sees there’s an “Astrophage” panel indicating consumption rates. There’s also nine fuel cylinders indicating Astrophage levels and an option to “jettison” the fuel tanks. The ship also has a “spin drive” propulsion system of some sort that he’s unfamiliar with.
He pieces together that the Astrophage serve as extremely energy-efficient fuel for the ship. They are kept in the fuel tank, but also along a shell all around the ship’s hull. He also sees that the hull’s temperature is at a consistent 96.415°c all around.
The temperature reading triggers a memory from Ryland’s second day at the lab. He recalls how he’d measured the Astrophage’s ambient temperature at 96.415°c, and he’d been unable to adjust that temperature, so he knows they are able to moderate their body temperature.
Ryland also asks why no other scientist are working with him, and Eva admits that he’s basically a guinea pig since they don’t know how dangerous those dots are yet. Ryland points out that (unlike in the movies) pathogens generally evolve over time to attack specific hosts so it’s unlikely these dots would “infect” humans. Eva says he’s doing fine on his own for now.
As he continues, despite his best efforts, Ryland is unable to find anything that can penetrate the little dots, including gamma rays. He then tries using a nanosyringe and to his surprise, it goes through. When he pokes one of them, it goes from pitch black to translucent, ruptures and dies. Eva sardonically congratulates him for being the first human to kill an alien.
With the membrane punctured and defensive mechanisms downed, Ryland is now able to run the tests to determine its chemical composition. He finds out that the Astrophage is primarily hydrogen and oxygen, so it’s a water-based life form that’s able to live on the sun by moderating its temperature. Ryland defeatedly admits that his prior academic research may have been wrong. Now that they know what it’s made of and that it’s water-based, Eva subsequently decides Ryland’s services are no longer required.
In present day, Ryland continues exploring the ship and access its storage chamber. He finds a bunch of uniforms and dons one of the jumpsuits plus a pair of booties. He also recognizes the names on them. Commander Yáo Li-Jie was the Chinese man from CNSA (the Chinese National Space Agency). Olesya Ilyukhina was from Roscosmos (the Russian space agency), and Ryland remembers how infectiously funny she’d been.
Ryland decides to dress the corpses as well so they can be buried in uniform. He then moves them into the airlock and jettisons the bodies into space.
In another flashback, Ryland is back in science class with his students the day after identifying that the Astrophages are water-based life forms. His students ask about what’s going on. He explains that the Astrophages are absorbing a small percent of the sun’s light, but that’s enough to be a big problem. As a comparison, all the problems associated with climate change have happened because of a shift in earth’s temperature upwards of only one and a half degrees. Depending on how quickly the Astrophages reproduce, scientists are predicting a drop in temperature of possibly 10 to 15 degrees within the next 30 years.
Thinking about the implications of all of it, Ryland goes back to the lab to ask Eva to continue working with the Astrophages. However, Eva says they only have 173 of these dots, excluding the one he killed yesterday, and they’re being distributed among 30-ish labs. He continues to plead his case until she agrees to leave exactly 3 specimen with him to test.
Ryland returns to the screens to try to understand what his mission was here. He sees something about “Beetles”. Named after the four members of the Beatles, the schematics indicate these are four smaller vessels whose shape vaguely resemble beetles, and Ryland figures out that they are unmanned probes. Each has an on-board computer with space for 5 terabytes of data storage.
Looking at Hail Mary’s fuel consumption rate, Ryland calculates that its fuel will be depleted in 40 just days. And at his ship’s current speed, it probably took years to travel to a solar system outside Earth’s. Ryland realizes then that he’s on a one-way trip and will die alone out here. His mission is most likely to load up copies of data and findings into each of the Beetles and send them back to Earth (there’s four for redundancies in case some don’t make it).
Ryland then recalls investigating his three Astrophages, which he names Larry, Curly and Moe. In a Nairobi lab, it was confirmed that the Astrophages can survive in Earth’s atmosphere. The Belgians found that they reacted to magnetic fields, albeit inconsistently, enabling them to “steer” the Astrophages. Paraguayans found that ants became disoriented around Astrophages. And in Perth, they established Astrophages had DNA and mitochondria, so they really aren’t that different from Earth-based life forms.
Ryland decides he’s interested in their life-cycle and understanding what would prompt them to travel back and forth from the Sun to Venus at nearly the speed of light (more specifically, 0.92 the speed of light).
Ryland sets up a lightproof closet and IR camera to track their movement, but he soon realizes they’ve stop moving. He tries placing a light source to attract them, but they still don’t budge. He sets it to the same frequency of IR light emitted by Venus, but still no dice.
Finally, he theorizes that they may have been attracted to the spectral signature of the carbon dioxide from Venus, since the planet is almost entirely composed of carbon dioxide. An experiment confirms this, but Ryland also manages to lose track of his 3 speedy Astrophages in the process.
Determined to find them, Ryland seals off all light sources in the room, makes a makeshift set of IR goggles to view heat signatures and adjusts the range so they only show things that are greater than 90 degrees Celsius. Ryland is able to locate the three Astrophages on the light filter, but then sees that there’s a fourth (which he names Shemp). It means that they’ve reproduced, likely through mitosis (cell splitting).
Afterwards, Ryland tries his previous experiment again and notices how only 2 of 4 the Astrophages are responding to the CO2 spectral emissions. He theorizes that this behavior is explained by their life-cycle. Astrophages take in heat energy. When it’s sufficient, they migrate elsewhere to reproduce. After that, both the child and parent return to the sun and the cycle continues.
This explains why they’d travel from the Sun to Venus and back again. They are attracted to the carbon dioxide on Venus because carbon is required for the complex proteins in DNA, mitochondria and whatnot, and carbon is not found on the Sun. It also explains why they are inconsistently attracted to magnetic fields. They use the solar poles as navigational aids initially until they locate the carbon spectra.
Upon informing Eva about being able to induce reproduction in the Astrophages, she sends a helicopter to pick him up immediately, and they fly to Travis Air Force Base. From there, he’s taken on a fighter jet straight to Naval Station Pearl Harbor in Hawaii. Two more flights later via jet and helicopter, he boards a Chinese aircraft carrier where Eva, along with a group of other people, are waiting.
Eva explains that the people here are an international body that is spearheading an initiative called Project Hail Mary. Ryland is asked to explain how to reproduce the Astrophages, and a Chinese scientist confirms that it works. The “doubling time” (time required for a population to double in size) is estimated to be 8 days.
Exhausted, Ryland sleeps for the next fourteen hours. Upon waking, he finds a post-it note on his face from Eva that leads him back to the room where Eva and the others are assembled. There, Eva presents to Ryland top-secret data indicating that stars across the galaxy are getting dimmer, which means the Astrophages are eating at stars other than the Sun. The data indicates that they’ve been dimming for decades now. Once a star has dimmed by about ten percent, it stops dimming, though they don’t know why yet.
It also suggests that the Astrophages will “infect” any stars within an 8-light-year radius, which they assume means that the Astrophages can only survive for that long without a star. One notable exception, is Tau Ceti, a star approximately 12 light years away from the earth. It’s surrounded by other infected stars, but it alone has remained unaffected.
The plan is to send a spaceship to Tau Ceti is find out why it has not been affected. Ryland protests that they don’t have the technology to get there. However, Dimitri Komorov, a Russian scientist, says they’ve been studying Astrophage’s energy management, and they’ve established that they store energy as mass (consistent with E = mc2). Each Astrophage can store around 1.5 megajoules of energy as extra weight. They plan to use the Astrophages as fuel for the ship.
While their scientists work on finding the massive amounts of energy to store in the Astrophages, Ryland’s task is to work on breeding them since they will need two million kilograms of Astrophage.
In present day, as Ryland tries to come to terms with his impending death, he’s determined to complete Hail Mary’s intended mission. He reasons that he’s most likely in Tau Ceti’s star system, so now he needs to figure out what caused the Astrophage not to feed on it. (He also starts referring to the robot-arms as NannyBot, since it takes care of him.)
Ryland inspects the various instruments and tools on board, including a “Petrascope” (which he assumes can detect the Astrophage’s IR light). He also find a reading that shows that the Hail Mary’s engine will stop in a little over 5 days at its intended destination. He doesn’t know how long the trip really took, but the readout has space for enough digits that it took at least 3 years. Even more time will have passed on earth because of time dilation (the closer you travel to the speed of light, due to rekativity, the more time effectively “slows down” for you), at least 13 years.
In a flashback, Ryland recalls Eva asking him for input. She says that the space for the crew will be small, only 125 cubic meters. If they’re awake, research suggests it will result in them killing each other or having crushing depression to know they’re stuck in a tiny space for four years with their imminent death lurking towards them at the end. The alternative, says Eva, is a lengthy medically induced coma, but that often results in death or “mush for brains”.
However, Eva also says the there’s some Russian research that suggests there are gene markers that give some people have “coma resistance”. The difficulty of the plan, is that one 1 out of every 70,000 people have the gene markers. This means it’s unlikely they’ll be able to send the most qualified people for the job. And they need to develop a robot to care for those people, technology which doesn’t exist yet.
In present day, Ryland wonders why Yáo and Ilyukhina died despite having the right genes, and then he figures the robot came across a situation it didn’t know how to deal with.
Ryland continues to catalogue the ship’s resources as he waits for it to reach its destination, where he’ll be able to start investigating the Astrophage problem. He sees that he has a digital library with access to any textbook or scientific paper or the book or reference manual. He also figures out for to load data into the Beetles and send them back to Earth.
The ship finally stops at a distance from Tau Ceti matching the distance the Earth is from the Sun. When the engines shut off, Ryland momentarily freaks out due to the lack of gravity, and he vomits resulting floating bits of gross stuff everywhere.
As he settles down, he turns on the Petrovascope (which detects the Astrophage’s IR signature). He sees that Tau Ceti, does in fact, have a Petrova line which indicates the presence of Astrophage.
Then, on his screen he also notice a flash of light that grows brighter and then disappears, though he doesn’t know what it was. He finally realizes his view is being blocked by another ship, the construction of which appears to be alien in nature.
Frantically looking around his controls, Ryland sees that the other vessel is 217 meters away. It’s much larger, though he recognizes that it’s also Astrophage-powered. Ryland sets the ship to manual control and flares the engine quickly to see if the other vessel will react. It does the same thing. Ryland then does three short blasts, and again the other vessel (which he names the Blip-A since that’s the panel it appears on) responds in kind.
From the telescopic cameras, Ryland is able to see that there’s a track around the hull of the other ship and what appears to be a robot traversing it. It comes around to the side closest to Hail Mary, holds up a cylinder and releases it.
Ryland figures he should assume they aliens are friendly, since if they want him dead he really has no defense anyway. Ryland rushes to put on an EVA suit (space suit!). There’s no decompression needed since apparently the entirety of Hail Mary is at 40% pressure.
Ryland finds that his prior EVA training comes flooding back to him. He’s able to easily intercept the slow-moving cylinder. But he’s immediately hit with the smell of ammonia, though it seems to be a non-lethal amount. He also finds that the cylinder is hot. In the lab, everything is floating around, and Ryland scans his mind for memories of it…
In a flashback, Ryland recalls meeting with a woman named Dr. Lokken. She’d looked at the preliminary design for the lab (which had been made available for comments) and identified a critical flaw. Much of the lab equipment wouldn’t work in zero gravity, and there’s no way they can design and test zero gravity versions in time. Instead, she suggests they’ll need to turn the ship into a centrifuge to simulate gravity.
In present day, Ryland looks for a way to activate the centrifuge, which he locates on a panel. It involves the ship splitting apart and partially turning upside down. Five minutes later, the ship is spinning smoothly. By now, the cylinder has cooled somewhat. He looks outside to see that the other vessel is mirroring Hail Mary by spinning as well.
Initial tests show it’s not radioactive and that it’s made of xenon. This confounds Ryland because xenon is a noble gas and the cylinder is extremely hard. Inside, he finds 1) a scale model sculpture of a Petrova line with two spheres around it as well as 2) another “doohickey” representing a local star map model. Ryland figures out that on the scale model one of the spheres is meant to represent Tau Ceti and the other is a star named 40 Eridani.
As Ryland thinks though its meaning, he wonders if these aliens are from a planet orbiting 40 Eridani. Perhaps these Eridians are dealing with a similar problem of Astrophage eating their star?
On the star map, Ryland carefully figures out which star is meant to represent Sol (our sun), and attaches a wire and smaller sphere to represent Earth. In other words, he’s responding by saying that he is from Earth, which orbits Sol. He also adds a line of wax meant to represent a Petrova line on the sun, hoping it will let them know that we, too, are dealing with an Astrophage problem.
With that, he puts it back into the container, stops the centrifuge and launches the container back towards the Eridian ship. He waves before heading back inside Hail Mary. Then, he waits.
Hours later, Ryland excitedly sees another cylinder floating towards him. This time, the aliens aim for the airlock that he’d walked out of before, for Ryland’s convenience. Inside the new cylinder is another model of the two ships (his and theirs) attached with a tube, indicating that they want to meet.
Ryland is also concerned that the Eridian ship is likely extremely hot and full of ammonia. Still, he thinks about what the aliens may need to build a bridge over to Hail Mary. He decides to send them a piece of the hull so they know what material they are working with. He breaks off a piece he thinks is safe and tosses it at the direction of the Eridian ship. He’s relieved to see the Eridians intercept it, and he’s delighted when their robot mimics him by waving back.
As he waits, Ryland flashes back to a memory of Dimitri showing him the ship’s spin drive in action. Dimitri explains how the spin drive emits a dim carbon signature (light with 4.26 and 18.31 microns wavelength) to attract Astrophage to get them to “stick” to the surface and then it rotates and emits a brighter light to cause them to thrust towards the back of the ship. Dimitri additionally explains that instead of one large engine, there will be 1,009 small engines. That way if some malfunction, the others can compensate.
In present day, Ryland munches on a burrito, the proximity alert goes off when the Eridian ship approaches which now has a cylindrical tube extending out of it which appears to be xenonite. The robot’s arms then extends out to stick to Hail Mary’s hull around the airlock and pull her closer with a seal. Then, Ryland hears a noise that sounds like the tunnel is being pressurized.
As he exits his airlock, lets his air fill the tunnel and enters the tunnel. He sees that there’s a wall in the middle. Once he sees that it’s stable, Ryland removes his EVA suit and returns to the wall separator. He smells the ammonia and can feel the heat emanating from the other side. Then, he hears knocking.
Ryland knocks three times in response as well. There’s no further response from the aliens, so he senses there’s something he’s supposed to be doing.
The wall appears to be made of hexes of different materials. Ryland starts using an x-ray spectrometer to scan the hexes. They seem to be a variety of xenon-based compounds. Ryland guesses that they are unsure which compound is best suited for Ryland’s air so the hexes are meant as a test. Ryland’s part of the tunnel is also filled with his air so the aliens can sample it if they’d like.
Then, Ryland notices one clear hex in the wall and starts looking through it. A hand attaches to it with a arm extending outwards. As Ryland looks on, the hand shows him that they’ve created a teeny, tiny, xenonite model of him in his spacesuit and a tiny, xenonite scale model of Hail Mary. The aliens place the tiny spaceman into the tiny Hail Mary, indicating that he should go back into his ship.
Ryland gives a thumbs up and retreats. Thinking about the hard rock-like arm he saw, he decides to name that alien Rocky.
Back inside, Ryland peeks out to see that the hex wall is gone. The Eridian hull robot is now in the tunnel poking around and inspecting things. Ryland had left a lamp in the tunnel and the robot collects it, likely taking it to be studied. It’s now dark in there, which indicates that perhaps the Eridians’ visible spectrum is different from humans or they simply can’t see.
Ryland goes to get another lamp so he can see, and he hears another knock. When he looks, the hex wall is now all clear. Moreover, Rocky is standing there. The dude looks like a huge spider the size of a laborador. No eyes or face, but he has five legs. And he has some type of cloth clothing on.
Then, Rocky points to something and makes a noise that sounds like a whale speaking in chords. Ryland excitedly talks back. Ryland also sees that they’ve left objects on his side of the tunnel. They are spheres, one with Hail Mary embossed on it and the other with Blip-A.
Inside the Hail Mary sphere is a line of beads forming two rings, resembling a beaded handcuff. Inside the Blip-A sphere is a bunch of lines of beads with one ring and more beads hanging off the ring, like a necklace with ornamentation.
Ryland struggles to understand the meaning until it dawns on him that these represent atoms and the beads are protons. The connectors are chemical bonds. The Hail Mary beads represent the oxygen atom. Meanwhile, the Blip-A beads represent ammonia, and there’s 29 of the strings of Blip-A beads. So, it means that the Eridians breathe ammonia and they have 29 times more atmosphere.
Ryland realizes that the pressure of their atmosphere must be like living “a thousand feet deep” in an ocean, which is likely why xenonite is so indestructably hard.
Ryland is exhilarated, but he also has not slept in two days. He gets a clock, trying to indicate that he will return in 8 hours. Then, Rocky gets excited and comes back with their version of a clock, a cylinder with five squares with changing symbols in them. As Ryland watches the Eridian clock, he 1) sees a set Eridian numbers, 2) sees that they also read from left to right, 3) sees that their “seconds” equate to 2.366 human seconds and 4) sees that they use a base six numerical system.
After his 8-hour sleep, Ryland returns to find Rocky in the airlock along with a bunch of other stuff that’s in the tunnel now. To his delight, Ryland also sees that there’s an airlock within the airlock now, essentially a chamber where they can interchange objects.
Ryland does a show of jazz hands which Rocky now understands to convey approval. Then, Ryland holds up a finger which Rocky now understands to mean “one sec” while he runs to grab a tape measure.
Now that they have established time measurements, Ryland wants to compare units of length. Ryland places the tape measure in the airlock. The rubber on it turns liquid from the heat on the Eridian side, but Rocky seems unfazed by it and the lack of oxygen means the rubber doesn’t off-gas fumes.
However, Rocky simply plays with the tape measure, ignoring the markings. As Ryland watches him and thinks about the lack of light, it occurs to him that Rocky “sees” with sound. He uses sound waves and passive sonar to understand the environment. The (human) clock’s physical hands were discernible to him as long as the clock was touching the wall, but the ink printed on the tape measure was useless.
Ryland tests his hypothesis by gesturing to Rocky behind an aluminum panel, since sound waves can travel through it. As predicted, Rocky can “see” his gestures just fine.
In a flashback, Ryland recalls Eva attending a court appointment to answer to a copyright claim from the Intellectual Property Alliance regarding the digital library of data onboard Hail Mary.
Eva is entirely dismissive of the claim. She had merely gone to make a point to everyone that she is immune from prosecution from any crime on Earth, via a signed international treaty. And she has a preemptive signed pardon for any crime in U.S. jurisdictions. Plus, the U.S. Army answers to her. Upon making her point, she exits the courtroom.
In present day, Ryland goes to his “library” to find a waveform analyzation program. The Fourier transform is a very basic tool that will break down the chords in Eridianese into notes. Ryland returns to the tunnel and calls out for Rocky, but he isn’t there. He calls out to him, but there’s no response. Instead, Ryland forms shape expressing in Eridian numbers what time he’ll be back and leaves it in the tunnel, and he goes to sleep.
Ryland oversleeps and returns to find Rocky seeming mildly upset. Rocky has a balled up fist and points to the (now inaccurate) time that Ryland had posted. Ryland apologizes, hoping Rocky understands his meaning.
Then, Ryland gets out his laptop and points to the Eridian number “1” and says “One”. Then, Rocky points to the same number and makes a noise. Ryland notes the frequencies that represent “One”. They continue through the numbers, and also translate things like the jazz hands which translate into “yes”. The balled up fist translates to “no” and a corresponding sound as well.
Over the course of many hours, they translate several thousand words. Ryland feels his software is slowing them down, so he produces an inefficient but workable program using his rudimentary programming knowledge to translate Rocky’s speech into frequencies, look it up in his table and translate it into English. Meanwhile, Rocky seems to have photographic memory and doesn’t need to record anything. He’s also very good at math.
Finally, Ryland brings out some Astrophage, indicating the word “Astrophage” which Rocky translates. Then, Ryland tells him “Astrophage on my star. Bad” and is able to confirm that Rocky is dealing with the same problem.
Soon, Ryland needs to sleep again. He tells Rocky. Eridians apparently sleep as well, but not as much as humans. Rocky wants to watch. Rocky has a device so he can watch, but it’s broken. Instead, Ryland sets up his bed in the tunnel and goes to sleep.
For days, they continue translating and learning grammar. Each time he sleeps, Rocky watches.
Soon, Ryland is trying to convey mass. Rocky hands Ryland a sphere which he calls “26”. Ryland initially assumes he means the Eridian mass is “26” units, and Ryland devises a complicated makeshift method to calculate the mass in Earth terms (complicated because he is in zero-g and can’t turn on the centrifuge without displacing the tunnel).
However, it turns out Rocky was referring to the atomic mass of the ball, which is 26, meaning that the ball is made of iron. Since the knows the density of iron and can easily measure the volume of the ball, a little math can tell him the mass.
At this point, Rocky announces he must sleep, but he doesn’t know how long. Apparently, their sleep is unpredictable. Rocky also asks Ryland to watch him sleep, since he sleeps better that way. When Ryland asks why another member of the ship can’t watch him, Rocky’s voice moves down an octave (which Ryland guesses is an expression of emotion). Rocky says that his crew was originally 23 and now he is the only one left alive.
In a flashback, Ryland recalls Eva going to visit Auckland Prison to meet with Dr. Robert Redell who was serving a life sentence for seven counts of homicide due to criminal negligence. He’d been working on building a solar power farm in Africa when an accident occurred and people died. He also embezzled millions of dollars to fund his gambling addiction, but that’s not what he’s officially in jail for.
Redell is an engineer by trade and had e-mailed them a suggestion involving blackpanels to solve their energy problem (they need massive amounts of energy to breed and charge up/”enrich” their Astrophages). Eva says that helping them now could potentially lead to a reduction in his sentence.
He explains that they just need to anodize metal until it’s black, put glass leaving a one-centimeter gap and seal it with a good insulator. With enough square footage, it could generate the power they need. He suggests using the Sahara Desert. They need 2 trillion square meters and the desert is 9 trillion total. It will destroy the ecology of Africa, but after it’s all done the panels will be theirs, giving them the infrastructure to become the energy powerhouse of the world.
In present day, Ryland notes that Rocky sleeps every 68 hours or so. Ryland also notes how Rocky seems to be constantly needing to fix things, and his side of the tunnel looks like a workshop.
Today, Ryland talks to Rocky about how he’s here to understand why Tau Ceti is not infected. Rocky agrees, but he doesn’t know either. If he can’t get rid of the Astrophage on Eridani, his people will also die.
Rocky then asks why Ryland’s crew is gone. Ryland attempts to explain. Then Rocky tells him that he doesn’t know why his crew died. They all got sick, something having to due with a problem with their cells, and he doesn’t know why he managed to survive.
Ryland realizes that Rocky’s crew likely had radiation sickness. Ryland tries to describe it (fast moving hydrogen atoms), but it turns out Rocky’s civilization has never heard of radiation.
In another flashback, Ryland recalls Dr. Lokken updating on new research from CERN. By now, the Earth has cooled enough to counteract all the effects of global warming.
She says that CERN has figured out that Astrophages store energy using neutrinos. They make neutrinos when the free protons in them collide, created from the kinetic energy from the collision, a process called “pair production”. It explains the high temperatures of the Astrophages, because that higher temperature gives the protons the velocity (and associated kinetic energy) required for the reaction (must have a higher kinetic energy than the mass energy of two neutrinos).
Dr. Lokken also explains that they divide back up easily because each neutrino is its own antiparticle. When the neutrino divides, it becomes two photons. The energy in the photon determines the wavelength of a photon, which is why the energy in “one photon of Petrova-wavelength light” is the same as the mass energy of a neutrino.
As for how Astrophages keep neutrinos inside, Dr. Lokken says that they’re not sure, but it likely has to do with their “super cross-sectionality” which basically means they absorb or collide with matter that tries to get by.
Dr. Lokken then turns to the topic of radiation protection. Because the Astrophages block and absorb everything, the plan is to fill the hull with Astrophages to serve as a radiation shield.
One day, Ryland recalls, Eva had brought in a Frenchman named Dr. François Leclerc, a climatologist with a proven track record. Eva asks him about how and when the sun’s dimming will affect humans. Leclerc says his estimate is that in 19 years, half of humanity will be dead. As he describes a litany of weather-related aberrations and phenomena, he explains that his calculations are based on the destruction of agriculture and famine.
Eva then says that they need at least 27 years, since Hail Mary will require at least 26 years to go back and forth. She tells Leclerc to look into producing greenhouse gases in order to heat up the Earth, ignoring his protestations about the morality of it all.
In present day, it takes Ryland a few hours to explain radiation to Rocky. Apparently, Blip-A has no radiation protection. Their planet, which Ryland names Erid, is very close to 40 Eridani. This means it spins quickly, giving it a much stronger magnetic field (since it also has an iron core, like Earth). It also has a thick atmosphere.
The magnetic field and atmosphere provide natural radiation protection. So, whereas life on Earth has evolved to deal with small amounts of radiation, Eridians have not.
The strength of xenonite allowed them to develop and discover space travel more easily but they never left orbit. Instead, Rocky and his crew were the first Eridians to do so. As they talk, Ryland learns that Rocky spent most of his time in the workshop of the ship, which is near the engines and the fuel. So, he was surrounded by Astrophage which protected him from radiation. Ryland advises him to surround the walls of his side of the tunnel with Astrophage.
When Rocky asks why Ryland doesn’t need it, Ryland neglects to tell him that he is on a suicide mission.
Ryland ponders why Earth and Eridians evolved for billions of years separately, but still ended up in approximately similar levels of scientific development at the same time. However, Rocky says it makes sense. A species with less scientific knowledge (and therefore no ability to build a spaceship) would’ve just died. With more scientific knowledge, they’d likely be able to to deal with Astrophage without leaving their planet. Instead, they are both here at Tau Ceti specifically because they are at similar levels of scientific development.
That said, Rocky also wonders if both Eridians and Earthlings were once “seeded” by the same ancestor (the “panspermia theory“) since they are close and their lives are similar in some ways.
Ryland’s memory flashes back to a very dejected Leclerc getting ready for them to destroy Western Antarctica, via a nuclear strike, to release greenhouse gases. Leclerc explains that Antarctica was once a jungle until it froze over. The methane gas from the decomposing plants is all trapped in the ice, and melting it will release them into the atmosphere, heating the Earth.
As a lifelong environmental activist, it feels contrary to everything Leclerc stands for. He also says that while it’ll keep things warm, it’s also going to cause the ecosystem to go haywire, with unpredictable weather and crop failures, so continuing to release greenhouse gas is not a good alternative to dealing with the Astrophage problem.
Right before the bombs detonate, Ryland asks Eva what will happen after Hail Mary launches, and Eva says that’s where her authority ends. She says she’s accepted she might be hauled off to jail for abuse of power, but it may be a sacrifice she needs to make. When the bombs go off, Leclerc cries.
In present day, Rocky and Ryland talk about their bodily physiology. The Eridians being so close to their sun means they have massive energy stores. Rocky’s body is mineralized, and his bones are metallic alloys. His blood is liquid mercury. When they sleep, their bodies are truly paralyzed, since that’s when their bodies are cooled so their cells can fix things which immobilizes their muscles. This means they cannot wake until it’s ready, which is why Eridians watch each other sleep.
As Ryland explains how he sees things primarily (as opposed to hearing things as Rocky does), Rocky asks about if Ryland “chose” the clear hex (on the wall with a bunch of hex options) because light passes through it. Ryland says yes.
Soon, Rocky announces that he plans on expanding the tunnel, and he’s built a life-support system for himself to be able to survive on Hail Mary. He wants to check out the technology on Ryland’s ship. He says they don’t have computers in Erid.
Ryland wonders how they pilot ships without computers. Even with their superior metal processing powers, it seems daunting.
Meanwhile, Rocky has now replaced the tunnel and is ready to enter Hail Mary. He is encased in a geodesic ball and wears his life support system on his back. He needs Ryland to move him around, and Ryland finds that Rocky is very heavy. He informs Ryland that he weighs roughly 300 lbs.
Ryland gives him the tour of the ship, and Rocky is most interested in the “science room” (the lab). Since many instruments needs the centrifuge to be on, Rocky suggests that he move into Hail Mary. Rocky will bring the materials needed to construct xenonite as well. That they, they can turn on the centrifuge, do science and figure out how to kill the Astrophage together.
Ryland flashes back to a memory of meeting Dr. Lamai, who was in charge of medical preparations for Hail Mary. Her company designed as the technology for extended comas, though it was discontinued when it turned out that a vast majority of people lack the “coma resistance” genes needed to survive extended comas.
The original intention was for the technology to be used for cancer patients to be able to “sleep” through chemotherapy treatment, but given the rarity of the necessary genes, there just wouldn’t be enough of a market to sustain a business.
Dr. Lamai shows them a set of metal-armed robots that care for the coma patients (precursor to NannyBot) and she admits that they are fairly rudimentary. Complex, but not intelligent.
When Dr. Lamai mentions the test for the “coma resistance” gene markers, Eva asks to be tested. Then, she tells Ryland to be tested, saying she wants everyone related to the project tested.
In present day, Ryland looks on in horror at the volume of stuff Rocky has brought on-board Hail Mary. Everything is muddy colored, since they have no need to visual aesthetics. Moreover, since Rocky is contained to his ball, Ryland grumpily carries all the stuff inside.
Once settled, Rocky is able to use magnets to get some stuff done from inside his ball. The first step is to sample the Astrophage, and Ryland remembers that Hail Mary has an External Collection Unit meant for the task.
Rocky originally had a tool for the task, but it was broken. When he talks about how long he tried to recreate it, Ryland asks how long he’s been there. Rocky says he’s been here alone for 46 (Earth) years and that Eridians typically live 689 years. Rocky is 291.
Rocky plans to make a room for himself to work on Hail Mary using xenonite. When Rocky seems unconcerned about how long it will take, he explains that Erid has around 72 years before the dimming will cause serious problems. Ryland reasons that this is because Erid has energy stores and a thick atmosphere. Ryland then explains that Earth does not have that much time.
Finally, Ryland tells Rocky that he’s on a suicide mission since there isn’t the fuel to get him home. However, Rocky says that if the issue is fuel, he has two million kilograms extra of Astrophage to get Ryland home. Ryland cries in relief.
In a flashback, Ryland thinks about the day they were presented with the Hail Mary flight crew. There were three primary crew and three backup crew. Eva has a rule that no crew member can travel with their backup, to prevent them both being taken out in one fell swoop.
Captain Yáo is primary commander. Ilyukhina is the primary crew materials expert. And Martin DuBois is the primary science expert.
Eva tells Ryland that he’s in charge of getting DuBois and Annie Shapiro, the backup science expert, up to speed on Astrophage biology. As DuBois greets Ryland, he mentions that Ryland also has the genetic markers for coma resistance, which Eva hadn’t told Ryland about.
In present day, Ryland gets up to date on all the observational data Rocky has meticulously accumulated over the past decades. They will now spend 11 days to travel close to a planet that orbits Tau Ceti, in a place that bisects the Petrova line as it orbits.
Ryland suggests that Rocky rename the planet they’re headed to (technically it’s “Tau Ceti e“) in Eridian. Rocky decides to name it after the name of his mate. So, Ryland decides to call Rocky’s mate (and the planet) “Adrian” (from the movie Rocky).
Rocky has previously explained that Eridians are hermaphrodites who reproduce by laying eggs next to each other (the equivalent of mating for life) which will result in one absorbing the other. After one Eridian year (42 Earth days), you get an Eridian baby.
When Rocky wants to eat, Ryland is eager to watch, though Rocky finds this intrusive. Rocky shreds up a bunch of rocks, his abdomen splits open, a gray blob comes out of him, and he puts the shredded rocks into his fleshy abdominal opening until its gone. At that point, Ryland realizes that the Eridians eat and defecate out of the same opening and do it at the same time.
Ten days later, they are nearly in position close to Planet Adrian. Ryland flashes back to a memory of himself testing equipment.
In the flashback, Ryland is at NASA’s Neutral Buoyancy Lab at Johnson Space Center. While Eva insisted that any mission-critical tools be off-the-self products (with countless hours of consumer testing behind it), a few others are custom-designed for their mission.
Ryland, therefore, was assigned to test the IVME (“in vacuo microbiology equipment”) kit, a kit for testing microbiology in space. A guy, Forrester, instructs him on what to do.
Afterwards, Ryland heads over to a conference room for the next lesson with DuBois and Annie. Before Ryland starts, DuBois mentions that he and Annie are involved sexually. It’s not an issue for the mission since there’s no reason they’d be on it together, but they know it’ll end in one of them dying on a suicide mission.
In present day, they are now in orbit near Planet Adrian and the samples are ready to be collected. Ryland suits up and they successfully collects the Astrophage from the collection unit filter. Back in the lab, he starts running tests.
His first observation is that he was expecting to collect more Astrophage going in one direction than the other. If the Astrophage go to the planet to breed and return with their progeny, then you’d expect the side facing the planet would have double the Astrophage. However, in their sample. there are equal amounts on both sides.
Under a microscope, he sees that there is all sorts of other life mixed in with the Astrophage. Rocky is delighted and realizes that it must be why there’s a population discrepancy. The other life is consuming the Astrophage, meaning that the Astrophage has a predator.
This means they can take the predators back home and breed them. It also means that Adrian is likely the Astrophange’s home planet since it’s where its predators evolved as well.
Ecstatic about the discovery, Ryland teaches Rocky how to do a fist bump to celebrate.
In a flashback, Ryland recalls watching the 9th out of 16 test launches for Project Hail Mary along with the crew and others. Eva is not there, and Ryland is surprised when the crew refers to him as her “number 2”. They say it’s clear that he is special to her. Other agree that she considers Ryland to be her second in command.
In present day, Ryland is growing frustrated as they are unable to identify who the predator could be. Rocky suggests that perhaps the predator only lives in the lower atmosphere. Ryland then theorizes that the breeding grounds of the Astrophage might be the idea place, so the place where they can detect carbon.
They determine that the predators likely live 10 kilometers into the atmosphere of Adrian, but Hail Mary cannot fly that low, since it would burn up. Instead, the plan is to built a xenonite chain that extends down to collect samples. It’s complicated because Hail Mary needs to slow down (or else the line will vaporize), while maintaining altitude (or else they will go too low and die), while being at an angle to try to thrust away from the chain (or else it will burn up).
As they prepare, Ryland asks Rocky how they ended up with so much Astrophage. Rocky says that breeding was very easy because they didn’t have the heat production issues that Ryland had with paving the Sahara and whatnot. They just tossed metal balls with carbon dioxide into the ocean.
Rocky then describes how his journey to Tau Ceti ended up significantly shorter than expected, and Ryland realizes that the Eridians do not know about time dilation. Because of this, Rocky’s ship ended up with a lot of extra fuel.
Ryland recalls Steve Hatch, a relentlessly optimistic guy, coming to visit him to show him the prototype for the Beetle. He explains how the Beetle is self-contained and can navigate itself back to Earth from anywhere. It has a spin drive, like the Hail Mary. It orients itself using visible light from the constellations and goes from there.
Steve also explains that the Beetles can go much faster than Hail Mary. Hail Mary is limited by having humans within it, but the Beetles are made of sturdier stuff inside. Because of relativity, this trip takes them 20 months to get back (though 12 years will have elapsed on Earth).
After Ryland has explained relativity and time dilation to Rocky, they continue working on their chain. It requires 200,000 links and took two weeks to make. Finding space to store it is a challenge as well.
Finally, it’s ready, along with the sampler probe attached to the end of it which also includes a “life support system” that maintains the existing conditions below to keep the lifeforms alive. The release of the sampler is a success.
Afterwards, Ryland has to fetch the sample from outside with an EVA suit on while feeling a full gravitational force and while having no oxygen. Trying to get back into orbit beforehand would vaporize the sample. Ryland is tethered as he does this, though it was designed for zero-g. They’ve designed a winch that pulls up the chain, releases one link at a time, and lets the chain link fall down (since otherwise the full chain would be too heavy to hold all in one spool).
After a long time, Ryland finally sees the sampler at the end coming towards him. Before it reaches the end, he detaches the sampler, attaches it to himself and prepares to go inside. However, at that point, the ship suddenly shudders and starts thrusting in the wrong direction. Ryland struggles to get to the airlock to fix things before the ship capsizes and kills them both.
Panicked, Ryland struggles to get the ship back into orbit, which requires velocity. It takes ten very tense minutes, and the hull strains the entire time. Ryland relaxes once it’s over, but then he notices that gravity is increasing (or at least something that feels like gravity) when they should be at zero-g.
With dread, Ryland and Rocky see that the hull near one of the fuel tanks has been breached by the heat. Even more problematically, the Astrophages who are eager to breed are now pouring out of the ship’s fuel tank, creating even more thrust. Unlike the controlled thrust from a working engine, this is messy and dangerous.
Ryland jettisons the damaged fuel tank, but the problem continues. Ryland knows that must mean there is another breach, most likely next to the previously jettisoned tank. Not having time to ascertain which one it is, he randomly chooses one of the two tanks next to it.
It works, however, the force has caused the ship to spin excessively. As the centripetal force increases, Ryland’s chair breaks and it weighs him down due to the force of simulated gravity. Ryland feels dizzy since it makes him unable to breathe.
With horror, Ryland sees that Rocky has exited his area to save him. Rocky removes Ryland’s restraints and the chair. Before he stops moving, Rocky tells Ryland to save Earth and save Erid.
Ryland makes it over to a panel, remembering that there’s a button to automatically adjust to stop rotation. However, he knows that will activate the spin drives which he doesn’t want to do. Instead, he turns the ship over the manual control over the centrifuge action. By increasing the radius of the centrifuge, he’s able to decrease the force he’s feeling by a squared amount.
Thankfully, it works, though everything in the ship is a mess and out of place and upside down. Ryland straps Rocky to himself and tries to make his way to the center of the centrifuge where the gravitational force is weakest. He manages to get Rocky back into his environment, but the broken airlock controls means a blast of ammonia enters the dormitory area.
Unable to breathe or see and feeling pain and numbness, Ryland asks the computer for help and thankfully feels the mechanical arms grab him and poke an IV into him before he’s unconscious.
When Ryland awakes, the computer tells him that he’s been asleep for six hours. Rocky is still unmoving. Ryland’s lungs still hurt, likely due to chemical burns from the ammonia blast. The ship is stable though everything is upside down. Ryland brings up the centrifuge screen to rotate the crew compartment to get things right side up.
Next, before he can focus on Rocky, Ryland needs to ensure the samples are safe so it wasn’t all in vain. Ryland measures the atmosphere of the sampler and finds a container to put it in with the same atmosphere, though he’s not able to chill the air in there to match Adrian’s. He puts some Astrophage in there so the predators, if they are in there, will have food.
Now, Ryland tries to review what he knows about Eridian biology to think of what might help Rocky if he’s still alive. Ryland knows that Rocky has just been exposed to a lot of oxygen, which must have oxidized Rocky’s insides. Ryland has been letting Rocky’s body heal itself and in the meantime he has built a box with a high-powered air pump.
While it sets, Ryland focuses on a micro-breach in the hull, which he goes to repair with some epoxy and a metal patch.
Ryland then goes back to his box which he has fashioned to be able to blow high-pressured air at Rocky. The goal is to help clean out his vents. When Ryland finally hits the right spot, a cloud of black smoke rises. He goes through each vent until it’s no longer producing more soot and dust.
In a flashback, Ryland sits down with the primary crew to talk. He asks them how they would like to die, since that is how the mission will end for them. DuBois prefers nitrogen asphyxiation and explains the equipment needed to do so. He says research suggests it’s the least painful way to die, and all you have to do is put on an EVA suit and hook it up to a nitrogen tank instead of oxygen.
Ilyukhina decides she wants to die of a heroin overdose. She’s never used drugs and wants to enjoy the initial doses. Then, she wants a lethal dose, possibly mixed with other drugs to reduce pain, that will kill her.
Finally, Yao wants a gun. He says he’ll be the last to die, so if something goes wrong with the methods from the other two, then he can kill them.
In present day, Ryland awakes to hear Rocky tapping on the airlock wall. Ryland is excited and tells Rocky what happened. When he explains about the air-blower, Rocky tells him the black substance is created by his body to help heal him. Luckily, he was healed enough when Ryland blew it out that he didn’t die.
Ryland goes back to sleep, and when he awakes they both are feeling improved. Rocky has created a new box for the Adrian sample, since Ryland had accidentally sealed it completely before with no way to retrieve the sample.
As they work, they talk about evolution. They discuss how Eridians can hear high and lower frequencies than humans. To the extent it overlaps with what humans can hear, it’s probably because the overlap range is an evolutionarily beneficial range. Meanwhile, they both ended up at similar intelligence levels, perhaps because that was the minimum intelligence needed to be able to dominate their planets and rise to the top of the food chain.
Flashing back to nine days before the launch, Ryland remembers ponders how he somehow ended up as an administrator. As he reviews some reports, there’s a flash outside his window. Its followed by a huge, glass-shattering explosion and then silence. Eva soon tells him that the research center has blown up.
DuBois and Shapiro are supposed to be there doing Astrophage experiments. Yao and Ilyukhina quickly confirm that they are okay. Eva, Dimitri and Ryland are taken to a safe bunker, as are Yao and Ilyukhina, until they sort out what happened. It’s soon confirmed that DuBois and Shapiro are dead, which means they need a new science specialist immediately.
In present day, Rocky is unhappy with Ryland for leaving the sample at room temperature for so long. Rocky has taken away the box from Ryland until he is able to sleep without painkillers, since clearly the pain is affecting his cognitive abilities.
When they finally are able to inspect the sample, Ryland finds it brimming with life. As he watches, an Astrophage is attacked by an amorphous amoeba-like blob which envelopes the Astrophage. Then, the Astrophage becomes translucent and dies. Ryland decides to name it Taumoeba, since it is an amoeba found on Tau Ceti.
Soon, they’ve breed the Taumoeba now they’re concern is whether they can survive on Venus and Threeworld (third planet is Rocky’s homesystem), since that’s where they are breeding near the Sun and 40 Eridani, respectively. They create chambers to simulate the environments, put the Astrophage and Taumoeba inside, and wait.
Then, it goes dark.
In Hail Mary, everything has turned off. Ryland can’t see so Rocky guides Ryland to the control room. The only light is a faint, red LED. Ryland is able to turn on an LCD display next to it that shows that the primary and secondary generators are off. The only power available is the emergency batteries.
Ryland powers up the emergency batteries, but still needs to figure out how to get the generators working again. When the computer boots up, the screen reads “TROUBLE” and has what looks like a “safe boot” type screen in three languages.
Ryland has Rocky try to identify if there are compartments within the storage space, and soon they’re able to locate the generators. He opens the fuel compartment and it smells bad, and Rocky suggests perhaps it’s the smell of dead Astrophage. Ryland then realizes the Taumoeba must have gotten into the fuel supply and are eating the Astrophage. As Ryland checks out his fuel lines, he confirms that it’s filled with Taumoeba and Taumoeba poop.
Ryland is panicked, but Rocky tells him to go to sleep while he cleans out the generator at least. Ryland agrees since he hasn’t slept in a long time. He wakes up to a sealed and functional generator, which they are able to install.
The next issue is how to get back to Blip-A to replace the fuel supply. The Beetles contain uncontaminated Astrophage and spin drives, but Ryland needs to first get to them at the nose of the ship while the ship is still spinning. Ryland also needs to be careful when removing the Beetles because he needs the nose of the ship to be intact if he wants to get home somehow.
After Ryland extracts one of the Beetles, he passes it off to Rocky, who works on modifying the Beetles. He modifies three of them — Ringo, John and Peter — while Ryland leaves George unmodified. Thanks to the Beetles and some careful maneuvering, they are able to stop the spin of the ship and focus on finding their way back to Blip-A.
In a flashback, Ryland recalls being called to a meeting after the research center incident. They’ve established that DuBois had been testing out a rare failure case in the generator, which would cause too much Astrophage to end up in the reaction chamber in the event of a pump failure. However, the research center gave him an incorrect amount on Astrophage to test on, causing a huge explosion instead of a much smaller one. Ryland is told there isn’t time to train someone properly, and he’s the best candidate right now because he’s essentially been training for years for this. Yao says that he’ll only take Ryland if Ryland goes willingly.
In present day, Rocky is maneuvering the ship via the modified Beetles to get them back to Blip-A. Meanwhile, Ryland gets to work in the lab. However, both he and Rocky are devastated when Ryland sees that their Taumoeba experiments have failed. In both the Venus and Threeworld environment simulations, all the Taumoeba are dead.
Ryland flashes back to the memory of talking with Eva after being asked to join the primary crew. Ryland had told her he didn’t want to go, and she had called him a coward. When he truly had refused, Eva had decided to keep him in a cell until the launch and to give him a sedative during it (to prevent Yao from knowing that he was an unwilling participant). She also gave him a shot of something that gave him retroactive amnesia so that he wouldn’t remember their conversation until later. Eva is confident that he’ll do the right thing when he does eventually remember, because he’s a good person.
In present day, Ryland is ticked off that Eva was right about him.
Considering their Taumoeba problem, Rocky points out that they know the Taumoeba can thrive in difficult environments, because they have a fuel tank full of them. Ryland starts thinking that they just need to first start by putting them in a chamber of just carbon dioxide and then add gases until they know what the problem is.
To properly test things, Ryland wants to put the ship back into centrifuge mode, though they know it’s risky. They manage to get it working without a hitch, though, and Ryland begins his testing.
Ryland’s findings: Taumoeba can survive anywhere between -180 Celsius and 107 Celsius. They require at least a little carbon dioxide to survive. Nitrogen kills them.
Both Erid and Earth need nitrogen to survive, and Venus and Threeworld both have nitrogen in their air. So, Ryland determines the only way for this to work is for them to find a way to breed nitrogen-resisant Tauomoeba. Rocky excitedly goes off the build the necessary equipment for Ryland to do this.
Soon, Ryland has bred Taumoeba are able to handle 0.01 percent nitrogen. The plan is to keep breeding and filtering out the one most resistant until their resistance gets higher and higher. He’s using nine different tanks. They need to get to 3.5 perfect for Venus and 8 percent for Threeworld.
As they are approaching Blip-A, one of the Taumeoba tanks is at 0.6 percent nitrogen. When he left his ship, Rocky left the Blip-A to briefly thrust its engines periodically to make it easier to find later, which they are now using to help guide them.
With Taumoeba-35, they finally have a strain with 3.5% percent resistance, which means Earth could be saved. Ryland is giddy with excitement. Meanwhile, they still need to get it up to 8% to save Erid.
They’ve also reconnected to the Blip-A. Rocky asks for a laptop as a gift, and Ryland agrees since he has many of them, though he warns that Erid will likely be too hot for the laptops to function. (Rocky has a camera that can convert the text, and Ryland agrees to teach him the letters.) In exchange, Ryland asks for some xenonite, in both solid and liquid form and Rocky readily agrees.
Next, Ryland works on cleaning out the fuel tanks in preparation for the new fuel. Then, he’ll do a nitrogen cleanse, since even one remaining Taumoeba can reinfect everything. In the meantime, Rocky checks on their tanks which are now at 5.2 percent nitrogen resistance.
After they are patched, cleaned and sterilized, Ryland does a test of dividing a few kilograms of Astrophage among the various tanks. Two bays end up still being infected, and the fuel lines still need to be tested as well.
Later, Ryland has still not been able to get the Taumoeba out of Fuel Bay 5. He finally jettisons it. The less fuel he has, however, the longer the trip home will take. The biggest issue is food. He only has 43 months worth of food (mostly because his crewmates died). Rocky’s food is toxic since it contains heavy metals.
As Ryland angrily sulks about his problem, Rocky tells him to just go to sleep. He says he will build another fuel tanks in the meantime. Soon, Ryland has three new fuel tanks to replace the missing ones. They are made out of alloy instead of aluminium, but they don’t need to be particularly strong, they just need to hold Astrophage.
The Taumoeba are now at 8 percent, and the two happily fist bump. Ryland goes searching in the kits of personal belongings to find alcohol and finds some vodka in Ilyukhina’s bag. Rocky puts on a celebratory outfit.
Now, the plan is to build mini Taumoeba life support systems for each of the Beetles, so a sample of Taumoeba can be sent with each one. Rocky will also transfer over his excess Astrophage so Ryland can go home. Rocky suggests someday they come visit each other, but Ryland reminds him that he probably won’t live long enough for that technology to be developed.
Soon, Hail Mary is fueled up and Rocky’s laptop is encased in its own life-support system. Meanwhile, Rocky has six colonies of Taumoeba with 8.25% nitrogen resistance. Ryland has his ten tanks with the mini-life support that he will put into the Beetles.
Ryland has calculated the distances for their trips, taking into time dilation in Rocky’s case. They say goodbye, and Ryland heads home.
Ryland flashes back to being kept in his cell in the days before the launch. Eva comes by to talk to him, despite his requests for her to leave. She talks about how if they don’t prevent this, even after half the global population dies then there will be wars over food with the strongest militaries invading weaker countries. The wars will disrupt agricultural production and then even more will die.
In present day, Ryland think about what he’ll say to Eva when she sees him again. He has four years to wait. Ryland has also decided that he’ll stop at Venus and drop off the Taumoeba before he returns to Earth.
After a month, Ryland knows he’ll soon be reliant on coma slurry instead of real food, the prospect of which he does not look forward to. As he tries some coma slurry, he confirms it takes terrible and wonders if perhaps a coma isn’t preferable.
Ryland get to work on the Beetles. He wants them to be ready for launch at a moment’s notice, but Ryland is holding off on sending them off unless there’s a critical problem. They have a better chance of making it if they’re in the safety of the Hail Mary for longer.
However, when Ryland takes out the container of extra Astrophage to refuel the Beetles, he realizes it’s been infected with Taumoeba.
Ryland’s concern is not the extra Astrophage storage, which is done for either way. Instead, he wants to make sure that the Taumoeba do not infect his fuel storage again. Ryland suspects that the way they got into the fuel storage in the first place was the life support’s heating system, so he turns it off.
Next, he shuts off the engine, just in case there is any Taumoeba in the fuel line. Thanks to DuBois’s preferred form of suicide, he has a nitrogen tank available. He uses it to fill the entire ship with nitrogen while he puts on an EVA suit to survive.
Next he double checks that his breeder farms are airtight. He overpressurizes them a little so they buldge, that they if there is a leak the bulging will disappear.
Three days later, things seem to be okay and he’s checked on all of the fuel bays. He also installs a “Taumoeba alarm” which is basically just letting some Astrophage sample sit exposed. That way, if any Taumoeba are free they will attack it. The slide will turn clear (since dead Astrophage are clear) and an alarm will go off.
Ryland still doesn’t understand how the Astrophage container got infected in the first place. Taumoeba only seem to survive a week without food. Ryland checks his Taumoeba farms for leaks, using his slide test.
It turns out the mini-farms (the ones for the Beetles) are fine, but his main breeder tanks (the ones used to develop the nitrogen resistant strain) all have a leak somewhere. It seems impossible because nitrogen, an atom a million times smaller, is not leaking from them.
Ryland starts to wonder if Taumoeba have a way of getting through xenonite, but it doesn’t seem to make sense for them to have evolved this way. (The mini-breeders were not built in xenonite because Ryland had worried that humans don’t have the tools to open it without heat. So, those don’t leak. )
He runs an experiment. It confirms his fears. Epoxy and plastic are both effective barriers for both normal Taumoeba and Taumoeba-82.5. However, while xenonite is a barrier for the normal Taumeoba, it’s not for Taumoeba-82.5.
Ryland realizes that when he bred them to have nitrogen resistance, they developed another trait. They learned to “hide” in the materials of the container they were in. Because they were being attacked with nitrogen in these xenonite tanks, it made sense for them to evolve this way as well.
For Ryland, the solution is simple: to store Taumoeba in a non-xenonite tank. However, he knows Rocky’s ship is almost entirely made of xenonite and his fuel is Astrophage as well.
With the Hail Mary’s Taumoeba tanks secured in non-xenonite, Ryland now looks for the engine flare from Rocky’s ship and doesn’t see it. That means his Taumeoba have escaped, and Rocky is stranded. It’s been three days since he’s seen the flare so it means he likely wasn’t able to fix it in time.
Ryland is left two options: to fly home and be hailed a hero. Or, to send off his Beetles, rescue Rocky and save Erid. And die from the inhospitable environment and lack of edible food. Ryland cries.
After the Beetles are sent on their way, Ryland starts looking for Rocky. There’s a 20 million kilometer range of where he could be. He thinks about what Rocky might have done, knowing he’s stranded and that his people are dependent on him to solve this. Perhaps emit a radio signal? But there’s no way Ryland could detect it.
Ryland then realizes he can use his ship as a radar. By sending a burst of IR light (via his spin drives) in that direction, he can then use his Petrascope (which can detect even tiny amounts of that frequency) to see where any light bounces back from.
The first few times, Ryland sees nothing, but finally be sees a flash. Ryland sets a course for what he hopes is the Blip-A.
As he approaches the location, he sees nothing, and he’s too close to use the same method of radaring again. Instead, he uses the altitude adjustment spin drives to emit just a little light and barrels around to try to find a trace of Blip-A.
Finally, he spots something, as he goes closer, he sees that it’s the Blip-A. It’s now been three months since they parted. As Ryland tries to communicate with it, he gets no response. He wonders if Rocky is dead, but then Ryland realizes that Rocky likely doesn’t have a reason to turn on the equipment to check for stuff outside.
Not knowing what else to do, Ryland gets in an EVA suit and tries to get close enough to grab onto the railing on Blip-A, but that fails and he’s left desperately scrambling for something to grab on to. Finally, he manages to latch onto an antennae. Then, he takes a wrench and smacks the hull until Rocky notices.
Rocky is delighted to see him and tells him to get back into his ship so he can extend a tunnel.
When they are reunited in the tunnel. Ryland explains his discovery that Taumeoba-82.5 developed a way to tunnel into xenonite. Rocky then plans to make a nitrogen sterilizer before re-boarding Hail Mary, so they can go to Erid.
Rocky also reassures Ryland that his people will gather the Astrophage needed to send Ryland home, but Ryland tells him he doesn’t have enough food to get home. When Rocky suggests trying Erid food, Ryland is certain the toxic heavy metals will kill him. Then, Rocky suggests eating Taumeoba, and it occurs to Ryland that it might work.
Ryland has now been living on Erid for a few years. It turned out that he could eat Taumeoba for calories, but it didn’t give him the nutrients he needed. He has no idea what happened regarding Earth and whether the Beetles made it home.
The Eridians have helped to keep him alive, partially because he helped save them and partially because he’s of great scientific interest. He lives in a dome with a life support system. The Eridian scientists collective studied how to meet his nutritional needs and to make the vitamins. They’ve also cloned his tissue to make meat, which he eats. He’s eating human meat (meburgers), but it tastes better than the other stuff.
The high gravity has been hard on Ryland’s bones, and he now walks with a cane. By now, he’s roughly 53, but 71 years have passed on Earth since he was born. The dome also has lights to simulate day and night.
Ryland goes into a room in his bubble with a clear separator, where Rocky meets him with good news. Their scientists report that Sol (the Sun) has returned to full luminance. Ryland cries.
Hail Mary is still in orbit around Erid. The Eridians have offered to refuel it and restock it with what Ryland needs to go home. Now, Ryland knows that Earth is likely habitable. Still, it’s a long and lonely journey.
The book ends with Ryland unsure whether or not he will return to Earth as Rocky goes home to watch over Adrian while she sleeps. Before they part, Ryland and Rocky wonder about other life on other planets.