Project Hail Mary is a 2021 science fiction novel by Andy Weir - and a really good one. In 2026 it was made into a great movie. However, neither the book nor movie have a map of the relevant parts of space. I think it needs a map, so here's a map!
Warning: Spoilers ahead!
The following map shows our local stellar neighborhood. Every dot represents a rogue planet or a star system (a star system is a star or set of stars that orbit each other, along whatever objects like planets that orbit those stars). For brevity, I'll call each rogue planet or star system a "stellar object". The name of the stellar object is next to it. Near the bottom center of the map, labelled in bold, is our Solar System (a star system centered on our own star, Sol). All distances in this map are measured in light-years (the distance light travels in 1 year in a vacuum, where a year is Julian year of 365.25 days). If it helps you to visualize this map, imagine you're Polaris (the "North Star"), looking "down" towards our sun Sol, and only considering certain stars (approximately only the stars within 5 light-years of the distance from Polaris to Sol). The directed lines show the travel of Astrophage from Tau Ceti (center right).
Click on the map to see just the map (which will will enlarge it); more information follows the map.
The following sky chart shows where the stellar objects important in the book would appear as seen from Earth. Again, the direct arrows show the travel of Astrophage from Tau Ceti (bottom right). Tau Cei is in the constellation Cetus (the whale), Epsilon Eridani and 40 Eridani are in the constellation Eridanus (the river), and Sirius is in Canis Major (greater dog). The constellation Orion (the hunter) is slightly to the right of center. We can't easily show its transmission from WISE to Sol (our sun) because we're looking from the solar system itself. We could show an arrow growing from WISE and pointing to us, but that would obscure everything else. Constellation lines are shown to help identify stars.
You can also see the sky chart with a more limited range (showing the range from Tau Ceti to WISE 0855).
The rest of this page will focus on the first map (the stellar map), since the stellar map can help us better understand what's going on.
One challenge with maps of space is that space is 3-dimensional, but printed maps are 2-dimensional. This map shows, on a 2-D plane, the location of each object on a plane going through the celestial equator (a plane that aligns with the equator of the earth in 2000). In front of every name are square brackets containing the number of light-years the object is above or below this plane. We'll center its height on our own Solar System (so its "height" is 0.0). This map only shows the stellar objects between -5 and +5 light-years of height in the celestial plane, to make the map simpler. Here's an example that might help you understand the map: if we added Polaris (the North Star) to this map, we would add a dot almost on top of the Solar System and write the phrase "[430] Polaris" to note that Polaris is 430 light-years in height above us.
I have made a minor exception with Alpha Centuri, the star system closest to our own. Alpha Centauri is a triple star system, and its star Proxima Centauri so much closer to our Solar System compared to its other stars Alpha Centauri A and B that their locations are visibly different even at the scale of this map. Thus, instead of one dot, the Alpha Centauri star system has two adjacent dots, one for Proxima Centauri and the other for the pair Alpha Centauri A and B.
The directed lines show the spread of Astrophage per pages 95-96 (all page numbers are per the hardcover 2021 release). Centered on each directed line is the distance of that trip (shown in italics and measured in light-years). Note that the trip distance between each of these stellar objects is less than the 8 light-year maximum transmission range of Astrophage ("Judging from our data, we think Astrophage has a maximum range of just under eight light-years"). Some are close, such as the 7.8 light-year distance from Epsilon Eridani to Sirius, but they are all less than 8 light-years.
Let's follow the directed lines from their source.
Finally, according to the book, Astrophage spread from WISE 0855-0714 to at least 4 other star systems: Wolf 359, Lalande 21185, Ross 128, and our own Solar System (page 95). The novel goes back and forth chronologically, but almost all the events occur after the humans detect the effects of Astrophage on our own Solar System (the system gravitationally bound to Sol).
Astrophage has certainly spread to other star systems as well. The book specifically says, "Any star within that range [8 light-years] of an infected star will eventually be infected" and that Tau Ceti "is not infected [yet] every star around it is". For purposes of making a clear map, I've only shown the expected path of infection for the stars identified as infected in the book. Where possible, I show the spread as reported by the book, only adding information where it seems necessary. Adding the connections for the other stars would make the map more confusing, especially since infection paths would soon be impacted by stars outside the +/- 5 ly band I'm showing to keep the map simple.
Now let's deal with the weird case: WISE 0855-0714.
That path seems straightforward. However, WISE 0855-0714 is where things get weird on this map. First, a quick acknowledgment: the full designation of this system is WISE J085510.83-071442.5. That's too much, so we'll shorten it (sort of) to WISE 0855-0714 or sometimes WISE.
WISE 0855-0714 was only discovered in April 2014 and isn't actually a star. Its mass is so low that it can't fuse any atoms like a main-sequence star or a brown dwarf. It's only 3-10 Jupiter masses (MJ). Normal hydrogen thermonuclear fusion reactions require .08 mass of the Sun - so a main-sequence ("normal") star requires at least around 89 Jupiter masses. Its mass is even below 13 Jupiter masses, the minimum (limiting) mass for thermonuclear fusion of deuterium that is necessary to create a brown dwarf. Its temperature is not like a typical star either: -48 to -13 °C (-55 to 8 °F). Objects like these are often classified as a sub-brown dwarf. It could also be called a rogue planet. It's easy to quibble about categories. However, since it can't fuse any atoms, it's more like a massive rogue planet than a star in the usual sense, so that's what I'll call it here.
But could WISE 0855-0714 support Astrophage reproduction? All the other stellar objects on this journey are star systems. It's easy to imagine that they each have a star and at least one planet with the carbon dioxide necessary for Astrophage to reproduce. However, WISE 0855-0714 is different! Could Astrophage regain enough energy (possibly by reproducing) to travel to other stars?
Let's quickly deal with atmospheric Nitrogen. For unclear reasons, normal Taumoeba is killed by significant amounts of atmospheric Nitrogen. However, Astrophage (and humans) don't mind atmospheric Nitrogen. After all, Astrophage is happy to grow on Venus. So while we don't know if WISE 0855-0714 has atmospheric Nitrogen, it wouldn't matter given the story premise.
To see if it's justifiable that Astrophage could reproduce on WISE 0855-0714, let's first look at the Astrophage lifecycle (primarily from pages 84-85 and 90-91):
So, could Astrophage at WISE 0855-0714 eventually end up at other stars? At the very least this requires the Astrophage to find a location on WISE 0855-0714 with a temperature over 96.415 °C, so it can get energy. That way, Astrophage looking for an energy source (like a star) will have one to find. At first this looks impossible, since WISE 0855-0714's average temperature is -48 to -13 °C. However, averages hide a lot; in 2021 Earth's average temperature was 14.7 °C (58.4 °F) yet the highest and lowest air temperatures on Earth are likely more than 55°C apart (per "Climate Change: Global Temperature" by Rebecca Lindsey and Luann Dahlman, June 28, 2022, Climate.gov). What's more, there are places on Earth (like lava flows) that have locations with far higher exposed temperatures. WISE 0855-0714 is probably a gas giant, so Astrophage could simply fall into it until it found pockets where that temperature (energy) is available. In short, it's very plausible that it could find spots above 96.415 °C even though its average isn't that high. What's more, Astrophage would be attracted to such sources.
After Astrophage fills up on energy, it will need to find a way away from its energy source (its "star") by using a strong magnetic field. Again, this seems plausible. WISE 0855-0714 is likely to have a strong magnetic field. After all, all four of our gas giants have magnetic fields. So once it's filled with energy, it can simply follow the magnetic field that is almost certainly present.
Once it follows the magnetic field out, it needs to find a body with carbon dioxide. There are two possibilities: a moon and itself.
I don't know of any evidence that WISE 0855-0714 has a moon, but I don't think we've disproven it either. So if WISE has a moon with carbon dioxide, then that moon would enable astrophage to complete its cycle.
An alternative would be that WISE 0855-0714 itself could have carbon dioxide. It's plausible that the rogue planet has carbon dioxide somewhere. If that's true, the rogue planet could fulfill the role of both "star" (energy source) and "planet" (carbon dioxide source). Any Astrophage leaving the rogue planet looking for the "other role" has a good chance of rediscovering the rogue planet.
One hint: every star nearby, other than Tau Ceti, was infected with Astrophage. Yet different stars have different kinds of objects orbiting them. This suggests that Astrophage isn't picky about its carbon dioxide source. More generally, it appears to be quite flexible about its energy and material sources.
So I think it's plausible that Astrophage could reproduce completely at WISE 0855-0714.
The lack of energy on the rogue planet might even encourage Astrophage to go looking elsewhere for energy. The rogue planet wouldn't "look" as much like a star, possibly resulting in a faster spread. It's not clear if lower-energy Astrophage could make the trip to another star, given its lack of energy, but it might. I expect that eventually some Astrophage could gather enough energy to become fully enriched. We know that at least some fully-enriched Astrophage can make the trip.
No matter what, WISE 0855-0714 will have lower available temperatures compared to a star. As a result, it would have taken far longer for Astrophage to gather energy from this rogue planet instead of its usual diet of stars. I haven't tried to calculate that, but I suspect it would be a long time depending on the temperature available. Perhaps it's best if we don't examine this question too closely :-). Still, both humans and Eridians were able to cause Astrophage to reproduce, and Astrophage would have strongly attempted to reproduce, so I think it's at least plausible.
Here are some other related pieces of information.
First: Yes, Andy Weir is aware of this map. On 2022-12-26 I sent him a message that pointed him to this map. On the same day he replied, "That's awesome! Thanks for sharing. :)".
The 2026-04-05 version of this map corrects a bug and updates the underlying star data, so it looks slightly different:
Book Club Edition: Andy Weir and Project Hail Mary Live Q&A with "Project Hail Mary" Author Andy Weir has a nice discussion (here's an Alternative link to the video). In particular, Andy Weir walked through a spreadsheet that he used to calculate key parameters relevant to the book and make the whole story more plausible. Another great interview with him about the book is Triangulation 428 - Andy Weir's "Project Hail Mary", hosted by Leo Laporte, "A conversation with science-fiction author, Andy Weir".
Andy Weir has posted a detailed document about Eridian biology (noted here).
The world of Any Weir's Project Hail Mary, June 2051 shows a map imagining the Earth one month before the return of the Taumoeba samples, posted by rexnerdorum.
Project Hail Mary Wiki (fandom.com) is a community fandom site about Project Hail Mary.
StarForce: Alpha Centauri is a board game published in 1974 by Simulations Publications Inc. (SPI) that uses a game map based on the real world positions of stars. My page Project Hail Mary and StarForce: Alpha Centauri shows how Project Hail Mary maps to positions on the StarForce game board.
This map is based on data from the Wikipedia List of nearest stars and brown dwarfs. Putting Your Stars in Their Places by Greg Scalise (2003) explains how to convert the usual astronomical coordinate system into the X-Y-Z system used here. In the X-Y-Z system used here, Right Ascension of 0 degrees is directly to the right ('east') of the point (0,0). I created the map using a very common set of data analysis tools (which I already knew how to use), including Python, pandas, numpy, and matplotlib. The custom code that implemented this is in github.com/david-a-wheeler/plot-stars. The code is public and available as open source software if you want to examine or improve it.
The sky chart was generated using starplot (MIT license), a Python library for astronomical plotting built on matplotlib. Starplot draws the background stars and constellation stick figures from its Big Sky Catalog, derived from the Hipparcos and Tycho astrometric missions. We use starplot's MapPlot with a Miller cylindrical projection, query star positions by Hipparcos ID to place arrow endpoints precisely on catalog dots, and add custom gold labels for the story's key systems along with directed orange arcs tracing the Astrophage transmission path between them. The custom code that implemented this is also in github.com/david-a-wheeler/plot-stars.
Many science fiction stories use real star systems as part of their plot. In some cases those star systems are too far away to be included. For example, in Dune, the ancestral home of House Atriedes is the planet Caladan (Dan) in the star system Delta Pavonis (19.9 ly from Sol), the ancestral home of House Harkonen is the planet Giedi Prime (Gammu) in the star system 36 Ophuichi (19.4 ly from Sol), and the planet Arrakis (also Dune and Rakis) is in the Canopus star system (312.7 ly from Sol).
I love hard science fiction (where there's an effort to make the plot believable based on our current knowledge of science). Project Hail Mary manages to combine science, a sense of adventure, and a sense of humanity in one awesome book. I appreciate gems like this book!
Feel free to see my home page at https://dwheeler.com.
(C) Copyright 2021-2023 David A. Wheeler. This essay and map are released under generous Creative Commons Attribution 3.0 or later. Under its terms, you are free to share it and adapt it, but you must give appropriate credit. Please do give credit to me (David A. Wheeler) if you use it somewhere else!
