# Project Hail Mary Stellar Map

## 2021-11-31

Project Hail Mary is a 2021 science fiction novel by Andy Weir - and a really good one. However, the book doesn't have a map of the relevant parts of space. I think it needs one, so here's a map.

The following map shows our local stellar neighborhood. Every dot represents a stellar object of some kind (usually a star); the name of the object or system is next to it. Near the bottom center of the map is our Solar System (centered on our star, Sol). All distances in this map are measured in light-years (the distance light travels in 1 year in a vacuum). Below the map are more details.

Click on the map to see just the map (which will will enlarge it)!

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 center it 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 "[430] Polaris" to note that Polaris is 430 light-years in height.

The directional arrows show the spread of astrophage per pages 95-96 of the hardcover 2021 release. Centered in each directional arrow 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. 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 arrows. It's eventually revealed that Astrophage starts at Tau Ceti (near the right center). Astrophage then spreads to Epsilon Eridani. It eventually ends up on Rocky's home system of 40 Eridani (top right), and while the novel doesn't expressly say it, by looking at the locations of stars it's almost certain that astrophage spread from Epsilon Eridani to Rocky's home system 40 Eridani. From Epsilon Eridani it goes to Sirius, the brightest star in our sky (in part because it's relatively close to us).

From Sirius it spreads to WISE 0855-0714 (full designation WISE J085510.83-071442.5). 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'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.

It's a little dubious that if astrophage existed it would spread far from WISE 0855-0714, but at least it's in a decent place. Anyway, in the book, astrophage spreads from this rogue planet to at least 4 other systems: Wolf 359, Lalande 21185, Ross 128, and our own Solar System.

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.