Fiction meets real data
In Andy Weir's Project Hail Mary, an alien microorganism called astrophage is draining energy from nearby stars. Stars dim, planets cool, and life-bearing worlds run out of time.
But astrophage is not just a creature that eats stars. Its lifecycle links stellar energy to carbon-dioxide-rich planets: it charges at a star, uses light for propulsion, then reproduces where the right planetary chemistry is available.
Every object in this route is real, but thankfully the astrophage is a product of Andy Weir's imagination. The journey below uses real nearby stars and brown dwarfs to explore how the geometry of the solar neighbourhood can turn fiction into a data exercise.
The premise of Project Hail Mary is simple and terrifying: astronomers notice that the Sun's luminosity is dropping. Not by much — a fraction of a percent per year — but the trend is real and accelerating. Something is feeding on it.
That something is astrophage: a fictional single-celled organism whose cycle runs between a star and a carbon-dioxide-rich planet. The star supplies energy. The planet supplies the carbon dioxide needed for reproduction. In the Solar System, the visible clue is the Petrova line between the Sun and Venus. By the time anyone on Earth noticed, the Sun was already one of many victims.
A note on distances: this site normally uses parsecs — the natural unit when working with stellar distances inferred from parallax and other catalogue estimates, and the unit used throughout our other lessons. Here we use light-years, because that is the unit Andy Weir uses in the novel, and the human scale of the journey matters to the story.
Scroll through the tour below to trace the infestation through real space.
Sol · 0 light-years
We start at home. An astronomer has detected an anomalous spectral feature in solar observations — a signature that has no business being there. It becomes known as the Petrova line: a stream of astrophage moving between the Sun and Venus. Further study reveals the cause: the Sun is being robbed of energy by an unknown life form, and its luminosity is falling as a result.
The effect is subtle at first. But on a timescale of decades it will trigger catastrophic global cooling and the collapse of agriculture. Earth is on a countdown, and the clock is already running.
Looking toward Tau Ceti · 12 ly
Turn toward Tau Ceti. It is a Sun-like star: spectral type G8, slightly cooler and smaller than the Sun, about 12 light years away. To the naked eye it is unremarkable: magnitude 3.5, visible from the southern hemisphere.
But Tau Ceti is where the story's trail leads back to. In the novel's universe, astrophage has its origin in the Tau Ceti system, and Tau Ceti behaves differently from the infected stars around it. That exception is what sends humanity looking for an explanation.
Arriving at Tau Ceti
Tau Ceti up close. A quiet, solitary star. No known close stellar companions, a debris disc, and several candidate exoplanets. In the novel, the trail leads to a planet in this system: Adrian, a CO₂-rich world where astrophage can complete its reproductive cycle. Tau Ceti supplies the energy; Adrian supplies the planetary environment.
That matters because astrophage is not just eating stars. It is moving through a star-planet lifecycle: charging at a star, emitting light for propulsion, and migrating toward suitable CO₂-rich planets where reproduction can occur.
First spread · jumps of 5.5 and 10 light-years
From here, the tour becomes a model rather than a literal canon map. It follows nearby real objects to show how distance, brightness, and hidden stepping stones can shape an imagined interstellar spread.
In this reconstruction, Epsilon Eridani and 40 Eridani are the first major hops from Tau Ceti. The connecting lines show the migration routes — each one a crossing of the void, powered by stored stellar energy converted back into directed light at a precise, characteristic frequency.
Epsilon Eridani — the shortest hop from Tau Ceti, just 5.5 light-years. A young K-type star with a known debris disc and at least one confirmed exoplanet. Its proximity makes it a plausible first stepping stone in this model. It sits about 10.5 light-years from the Sun.
40 Eridani — 10 light-years from Tau Ceti, about 16 from the Sun. A triple system: a K-dwarf primary named Keid, a white dwarf companion, and a red dwarf. If you've read the book, you'll know why this system matters more than just as a waypoint on the infection map.
The relay · jumps of 7.8 and 4.7 light-years
In this model, the route crosses 7.8 light-years from Epsilon Eridani to Sirius — the brightest star in our night sky, twice the mass of the Sun, and pumping out twenty-five times its luminosity. For an organism that charges at stars, it is an obvious energy source in the neighbourhood. Sirius is 8.6 light-years from the Sun.
From Sirius, the model's next hop is a short one: just 4.7 light-years to WISE 0855−0714, a cold, solitary brown dwarf sitting 7.4 light-years from the Sun. You will not see it in the star field: it is far too faint to appear in either the Gaia catalogue (which this site is built on) or the older Hipparcos survey that supplies our brighter stars. Discovered only in 2014 by NASA's WISE infrared satellite, it is one of the coldest known objects outside the Solar System — around 250 K, colder than a winter night on Earth.
In this reconstruction, this invisible relic is the critical relay. Without it, the chain from Sirius to the Sun cannot close. The astrophage route here is driven more by proximity than naked-eye brightness: a dim nearby object can be a better stepping stone than a brilliant star farther away. WISE 0855−0714 is perfectly placed.
The last hops · jumps of 4–8 light-years
From WISE 0855−0714, this reconstruction fans out to four stars at once. The Sun was not special. It was simply nearby.
Sol — a jump of 7.4 light-years from WISE 0855. A G-type dwarf, middle-aged, stable, and utterly ordinary. By the time the dimming was noticed, astrophage had been feeding for years.
Wolf 359 — the closest hop of this final burst, only 4.4 light-years from WISE 0855. One of the faintest stars known, a red dwarf so dim it is invisible to the naked eye despite sitting just 7.9 light-years from the Sun. It became famous as the site of a fictional battle in Star Trek — and now, in another fiction, it falls to astrophage.
Lalande 21185 — 7.0 light-years from WISE 0855, 8.3 from the Sun. Another red dwarf, the brightest red dwarf in the northern sky. Quiet, cool, and ancient — possibly twice the age of the Sun. It has at least one confirmed exoplanet.
Ross 128 — the longest jump in this final fan, 7.6 light-years from WISE 0855, about 11 from the Sun. A red dwarf notable for its confirmed Earth-sized planet orbiting in the temperate zone. Ross 128 b receives about 1.4 times the flux that Earth gets from the Sun. If anything in this story could harbour life, this is where the odds are shortest.
Look at the shape of the web. Each hop follows a nearby viable object. The geometry of our corner of the galaxy — the actual three-dimensional arrangement of these real stars — is what determines the pattern of this modelled infestation.
40 Eridani · 16 light-years · looking home
We end in orbit around 40 Eridani — not just because it sits at the edge of the infection map, but because of what happens here in the novel. To say more would be to spoil one of the best surprises in recent science fiction. Read the book.
From here, the Sun is just another star: unremarkable, anonymous, lost among thousands of brighter points. Sixteen light-years is nothing on a galactic scale — and yet it is enough to make home invisible. The astrophage did not care about our civilisation or our history. In this story, it followed a brutal loop of energy, light, and planetary chemistry. Nearby systems became links in the chain.
Real geography
Every position in the tour comes from catalogue-derived stellar data — primarily Gaia, supplemented by Hipparcos for the brightest stars and by documented overrides where the story needs objects outside those catalogues. This route treats proximity as the main driver. Astrophage still needs stellar energy and a suitable CO₂-rich planetary environment to reproduce, but the shape of the model comes from our catalogue-estimated stellar neighbourhood.
The invisible relay
The critical stepping stone between Sirius and the Sun is a brown dwarf that neither Gaia nor Hipparcos can see — it is simply too cold and too faint for optical surveys. Only the WISE infrared satellite found it, in 2014. It is marked here by coordinates alone. This model's chain of infection depends on an object that barely registers as a star at all.
Scale
The entire modelled network fits inside a sphere of about 16 light-years radius. The Milky Way is roughly 100,000 light-years across. This crisis is galactically microscopic — and yet it threatens every planet orbiting every star within reach.
Fiction & science
The stars are real, and their positions and distances are catalogue-derived estimates. Astrophage is fiction — no known organism feeds on stellar energy. But the spatial logic is genuine: this is how a nearest-neighbour model could move through this version of our corner of the galaxy.
The book
This tour is inspired by Project Hail Mary (2021). The novel follows a lone astronaut sent to Tau Ceti to find a way to stop the astrophage and save the Sun. If you have not read it, the less you know going in, the better.
