Adapted from the eponymous novel by Andy Weir, also the author behind The Martian, Project Hail Mary recounts the adventure of a humble school teacher who finds himself aboard a space mission to save humanity, with no idea how he got there. The film is a story of scientific brain-teasers, survival in a hostile environment and unexpected encounters, a human-alien adventure that paints a picture of the space quest that is both watchable and funny.

We viewed the film with Christian Mustin, CNES’s exobiology, exoplanets and planetary protection expert. As someone used to thinking about how life might have formed elsewhere in the universe, he relished this opportunity. His perspective helps us to distinguish solid scientific intuition from pure fiction.

Star-eating micro-organisms

First of all, the film offers an original take on microscopic lifeforms, as we encounter star-eating micro-organisms called “astrophages” notably consuming our own star, the Sun.

“It’s interesting that the first ‘alien’ we see in the film is a peaceful, unicellular micro-organism!” notes Christian Mustin. “Because today, far from the clichés of invading creatures or little green men, scientists actually working on the subject of extraterrestrial life are indeed looking for microscopic lifeforms. Mars, where the Perseverance rover is analysing surface rocks in search of signs of ancient microbial life, is a case in point.”

In the film, this extraterrestrial lifeform circulating between our Sun and Venus has a somewhat surprising life cycle: astrophages feed off starlight and breed in an environment saturated with carbon dioxide, thereby dimming the Sun and condemning earthlings to a gradual extinction!

“An organism like this capable of feeding off a star’s energy is an appealing concept, but its underlying mechanisms seem implausible on the basis of current science.”

On the other hand, the way the astrophages behave is much more rooted in science. “These micro-organisms don’t live in isolation, they belong to a community,” adds Christian Mustin. “It’s a microbial society where everyone contributes to the ecosystem’s overall balance. This idea isn’t at all trivial: here on Earth, microbial ecosystems are always diverse and interact in complex ways, based on cooperation and competition between species. This collective way of functioning is vital to ensure robustness and resilience.” Here, at least, fiction is pretty faithful to what we know about the ecology of microbes.

Encounter of a new kind

The main character subsequently has an unexpected encounter with an alien that he calls “Rocky”, who is also faced with the eventual death of his planet’s star because of the astrophages. The two join forces to try to find a solution. Obviously, their attempts at communicating give rise to much hilarity, but in Christian Mustin’s view these scenes are particularly well constructed. One of the first things he noticed is the encounter between the human and the alien.

Christian Mustin goes further: “This is a very interesting approach, based on a simple learning process similar to what some scientists see as how two radically different lifeforms might attempt to make contact and talk to each other.”

The film also does a good job of depicting the alien, as Rocky looks nothing like a human. He’s not symmetrical, he lives in an atmosphere we couldn’t survive in and his perception of the world is completely foreign to us. For example, he sees everything as being perfectly aligned, straight and with sharp angles… as a result, he can’t quite fathom all the weird “rotundity” of his human acolyte! This choice marks a departure from the conventional humanoid figures most often seen in movies, like E.T., Alien or Yoda, posing one of the questions that scientists are asking about extraterrestrial life: What might it look like? For Christian Mustin, this radical new approach is precisely what makes the character credible, reminding us that if there is life elsewhere, it could be very different to life as we know it on Earth.

An end with a nod to planetary protection

A less obvious point that very much appeals to Christian concerns planetary protection, in other words, the approach that aims to avoid contamination between Earth and extraterrestrial environments, in order to preserve our planet’s biosphere and the integrity of scientific research on other celestial bodies. The film offers a coherent vision of this side of things, notably in how it ends… which of course we won’t reveal! Our expert underlines that the fundamental principles of planetary protection have been adhered to, which in itself is commendable.

Carbon and water: the ingredients of life?

At several points in the film, the viewer is confronted by the question of what the astrophages and Rocky are made of. Are they like us, consisting mainly of carbon and water? This echoes alternative hypotheses about the possibility of life without these two elements, based for example on silicon or ammonia. But silicon chemistry isn’t flexible enough to form complex and varied molecules, like those produced by carbon forming the foundation of life on Earth. Likewise, water is a simple molecule found everywhere in the universe and its unique properties make it an ideal solvent for many chemical reactions needed for life to start.

“The hypothesis that life in the universe could be based on other forms of chemistry is an interesting one, but it remains fairly unlikely and inconsistent with current knowledge, unless we discover a second genesis somewhere in our solar system,” concludes Christian Mustin.

In the final analysis, Project Hail Mary offers a vision of science-fiction that seeks not just to overawe, but also to get us thinking. By probing real questions that scientists are asking, while also taking certain artistic liberties, the film strikes a compelling balance. For Christian Mustin, it’s precisely this combination that makes it an interesting viewing experience: a storyline that fires our imagination while getting us to think about what other intelligent forms of life might look like.