The stars, and possibly the planets orbiting them, where Project Hail Mary, now opening in theaters, takes place are very real. We’d expect nothing less from Andy Weir, whose reputation for scientific accuracy helped define modern “hard” science fiction.
The biology that drives the story, the discovery that pushes humanity to gamble everything on science teacher-turned-astronaut Ryland Grace (portrayed by Ryan Gosling), is fictional. The idea echoes real scientific research into planet–star feedback systems and atmospheric regulation, where life and environment influence each other in complex ways.
Project Hail Mary points directly toward where astronomy is headed: a deeper understanding of exoplanets, the worlds orbiting stars beyond our own.
The real star systems of Project Hail Mary in
- Sun (Sol) – our home system
- Tau Ceti – the mission destination
- 40 Eridani – Rocky’s home system
These are not arbitrary choices. Tau Ceti and 40 Eridani are among the closest stellar systems to Earth, making them ideal targets for interstellar exploration, once propulsion technology is sufficiently advanced to support it of course.
Tau Ceti: A Real Exoplanet System
In the novel, Tau Ceti is special because it resists the fictional Astrophage infection. In reality, it’s one of the most intriguing nearby Sun-like stars.
Tau Ceti is a G-type star, very similar to the Sun, which likely hosts a system of multiple planets, including up to 5 super-Earths. Tau Ceti also also has a massive debris disk, an oversized version to our own Kuiper Belt.
This star system is a frequent topic of discussion by astronomers a potential host of habitable-zone planets, although that dense debris disk is probably much more hazardous than our own..
40 Eridani: A real and complex system
Rocky’s home system, 40 Eridani, is also real, but very different from the single habitable-star system described in the novel and film.
The real 40 Eridani is a triple star system about 16 light-years from Earth, made up of orange, white, red dwarf stars.
While there no confirmed Earth-like planet in the 40 Eridani system, similar nearby stars, like Epsilon Eridani, do host planets, including gas giants like Jupiter and Saturn, and possible habitable candidates.
Writing a novel in Word and Excel
Weir, a self-described “hardcore science geek” spends as much time researching and calculating timelines and other numerical details in Excel as writing the novel itself.
Unsurprisingly, the relationship between the star systems is accurate and chosen for a reason. Tau Ceti and 40 Eridani and neighbors on a galactic scale about 12 and 16 light-years from Earth respectively. This detail is important to the novel’s premise hat nearby stars could influence each other and be studied in a single mission in a world where interstellar travel is possible.
Real exoplanets, fictional biology
The biggest scientific leap in the book is not the astronomy, it’s the biology.
While Exoplanets can influence their stars indirectly (e.g., through tidal forces or magnetic interaction) and we see our own planetary atmospheres can regulate climate every day,
The novel hints that life in different systems may share a common origin. Scientists call this theory panspermia, the idea that life can spread between planets.
While interstellar panspermia takes the idea to new extremes, scientists have long discussed the idea that meteorites could transfer of microbes between planets. If this seems far fetched to you, stop by the meteorite display at the North Carolina Museum of Natural Sciences in Raleigh, and touch a piece of Mars that fell to Earth in the form of a meteorite.
Weir scales that idea up to interstellar distances.