Extra-terrestrials have always been a fascinating subject for us humans. In the media, they have been portrayed from comically homicidal Martians in Mars Attacks to stoic Spock in Star Trek and the curious and childlike E.T. The latest to join the ranks of the non-earthling denizens of the universe is Rocky, the adorable rock-like Eridian from Project Hail Mary.
Rocky is unlike the humanoid lifeforms we have come across. He has five limbs, no face, no eyes, he uses echolocation to ‘see’, and speaks with musical chords. His ‘skin’ has a rock-like texture but is not rock. His species is far more intelligent than ours, with photographic memory and processing power surpassing human limitations, and is infinitely more empathetic. He’s bound to make you go “Amaze! Amaze! Amaze!” — a refrain in the film — but where could Rocky have come from and is there a chance he could exist in real life?
A special star
In the film, Rocky hails from the star system 40 Eridani. To visit him with our current technology is impossible. Even if you manage to cobble together a working starship, the star his planet orbits, 40 Eridani A, is 16.34 light years away, making a one way trip more than 2,80,000 years long if you travel at 17 km/s. But if you do visit Rocky, you could meet Spock as well: Vulcan also orbits 40 Eridani A.
What makes this star so special that we have not one but two alien species originating from there?
One of the main factors scientists look for when searching for potential extra-terrestrial life is a habitable zone: a band of space around a star where the conditions are just right for a planet to have liquid water on the surface, allowing life (as we know it) to evolve.
40 Eridani A does have a habitable zone 101.7 million km from it. Scientists had also glimpsed some evidence that there could be a planet orbiting the star but they haven’t been able to confirm it exists. The same ‘evidence’ can also be explained by variations in the star’s light output.
But if this planet exists, it also needs to have certain favourable conditions of its own to support life.
Life on Erid
From the information available on Rocky’s home planet, dubbed Erid, it would be eight-times heavier than the earth and orbit 40 Eridani A once every 42 days. If it is also as dense as the earth, Erid could be a rocky planet with gravity twice as strong as our own. However, Erid would also be only 33 million km from 40 Eridani A, and its surface would be too hot to sustain liquid water: it would boil off.
The only way to circumvent this problem would be if the planet had a high atmospheric pressure, which in turn would increase the boiling point of water, and a strong magnetic field. Since Erid is too close to its star, the chances are that its atmosphere will be blown away by stellar winds from 40 Eridani A unless it has a dense atmosphere like Venus.
Venus’s atmosphere is made of carbon dioxide and nitrogen blanketed by clouds of sulphuric acid. This creates a strong greenhouse effect that increases the planet’s temperature and pressure.
For Erid, author Andy Weir — whose book the film is based on — decided that the atmosphere would be composed of ammonia and that the planet would have a very strong magnetic field.
Senses for Eridians
Thus, Rocky and his compatriots would have an environment suitable for living, albeit a very hot (210 °C) and high-pressure one.
This is also why it is a miracle that Dr. Ryland Grace (Ryan Gosling) isn’t instantly killed when Rocky breaks out of his enclosure to save him. The enclosure has conditions preserving those on Erid, for Rocky’s sake, but between the high pressure ammonia gas and the heat flooding into the cockpit, Dr. Grace’s lungs should have been destroyed. In the book, however, Rocky uses the airlock.
With such a thick atmosphere, Erid will also have low visibility, which is why Rocky’s ship is so dark: he doesn’t need ‘eyes’ to function. Eridians would then have to have evolved other senses to get around. One of them is echolocation (like bats on the earth); another is that their rocky skin can ‘hear’ the vibrations that bounce off it.
The film also depicts an idyllic beach on Erid. It may not be a real beach so much as a specialised and temperature-controlled biosphere with perfect earth-like conditions inside.
Eating stars
Rocky isn’t the only alien in the film. The Astrophage, who is the film’s main antagonist, is also an extra-terrestrial lifeform. The Astrophage is like algae, except that it grows on the surface of stars instead of in the ocean. It is also a very efficient source of fuel. But on the flip side, its energy consumption levels are so high that it is capable of draining our own sun, taking our world right back to the ice age.
But the Astrophage is also not very scientifically sound: it is able to store energy only because of a made-up phenomenon called “super-cross-sectionality”.
Technically, us earthlings are also only one or two very-efficient fuel sources away from building our very own Starship Enterprise.
In the end, Project Hail Mary is still fictitious and requires more than a little suspension of disbelief to make certain things work. Nonetheless the film does a good job of reminding us that space is cool and science is amaze! Amaze! Amaze!
Rudraa Abirami Sudarshan is an astrophysicist, science communicator, and journalist.
Published – April 03, 2026 08:00 am IST
