Project Hail Mary, the new film adaptation of the 2021 science fiction novel by Andy Weir, is already a box-office hit after blasting off into theaters last Friday. 

The film, starring Ryan Gosling as a high school science teacher who must save humanity from an alien microbe that’s in the process of devouring the Sun, is being praised both for its realism and its effusive embrace of using science to solve problems (a common theme of Weir’s writing). And while not everything in Project Hail Mary passes the empirical smell-test, even the more speculative parts of the story offer an opportunity to explore some seriously cool science. 

One of Project Hail Mary’s most fantastical elements is Astrophage, the Sun-eating microbe at the center of the drama. The organism, which arrived in Earth’s solar system from the neighboring Tau Ceti star system, feeds directly on stellar heat. Some of the energy the Astrophage consumes is re-emitted as light, which the space plague uses for propulsion. Like a microscopic solar sail, Astrophage hop-skips across the galaxy, consuming stars and plunging their planets into eternal frozen darkness before moving on.

Biologists aren’t aware of any real life form that roves around space snacking on coronal mass ejections. But there are plenty of organisms — including most plants, some bacteria, and even a few pioneering animals — that eat sunlight. There are also microbes, like Astrophage, that can survive intense radiation and extreme temperatures. On Earth, there are even a few hardy life forms that can withstand the vacuum of space, at least for a brief period.

Here are some real life forms that share superpowers with the dreaded Astrophage. Let us hope they never evolve the ability to smother the Sun like fruit mold.

Photosynthetic sea slugs

No life form on Earth consumes heat directly, as Astrophage apparently does. But there are plenty of organisms that ‘eat’ the sun — absorbing a portion of its energy and using it to turn carbon dioxide into sugar. This process, known as photosynthesis, evolved billions of years ago and underpins nearly every ecosystem on Earth today. Without plants and their sunlight-consuming superpowers, our world would be biologically impoverished.

But plants are not the only organisms that snack on sunlight. And when I think of who does it in the most alien way, my mind turns to an animal. 

Elysia chlorotica is a brilliant green sea slug that looks like a leaf. It also acts like one—sort of. In an astonishing example of biological kleptomania, the slug eats algae and steals their chloroplasts, the tiny cellular factories responsible for photosynthesis. It also pilfers the genes involved in repairing and maintaining chloroplasts, allowing the stolen solar factories to ‘live’ on for months, making sugar from sunlight inside their new host.

E. chorotica bears little resemblance to Astrophage, but its unorthodox lifestyle is a reminder that evolution works in weird and often unpredictable ways. If we ever do discover life beyond Earth, we should not be surprised to learn that it, too, defies biological orthodoxy.

Radiation-resistant fungi

Radiation-resistance is high on the list of adaptations you’d need to survive in outer space, bombarded with galactic cosmic rays and damaging solar particles. Unsurprisingly, Astrophage is like a bomb shelter, deflecting everything from ultraviolet light and microwaves to the intense ionizing radiation associated with nuclear fallout. 

That’s impressive—but there are some mushrooms that can hold their gamma rays, too.

Several species of mycorrhizal fungi—fungi that intermingle symbiotically with the roots of trees—are capable of absorbing nuclear radiation. In particular, the fungus Gomphidius glutinosus can reportedly concentrate Cesium-137, one of the most dangerous components of nuclear fallout, by a factor of 10,000. 

In wake of the Fukushima nuclear disaster in Japan, fungal ecologist Paul Stamets called for establishment of a ‘nuclear forest recovery zone’ that would include native trees along with these radiation-chowing fungi. After sucking down a lethal dose of cesium-137, the mushrooms would be harvested and incinerated, after which their ashy remains would be turned into glass for long-term storage.

Stamets’ idea has not been implemented yet. But it’s heartening to imagine that even in the wake of an apocalyptic nuclear war, something would feast on the ashes of human civilization.

Heat-loving archaea

Astrophage has an internal body temperature of 96.4 degrees Celsuis–just shy of the boiling point of water. That’s hot, but there are Earth microbes that thrive in even hotter environments. In particular, several strains of archaea flourish in boiling hot springs, including Pyrolobus fumarii, which can survive temperatures of up to 113 degrees Celsius, and Methanopyrus kandleri, which chills in waters as hot as 122 degrees Celsius.

These so-called hyperthermophiles have unique adaptations that keep them from boiling alive. These include special heat-shock proteins and enzymes that prevent other cell components from falling apart, as well as membranes made of stress-resistant phospholipids. 

Heat-loving microbes offer insights into how life might have gotten its start in deep sea hot springs. They also provide tantalizing clues about how alien microbes may live in the subterranean seas of Jupiter’s icy moon Europa, or Saturn’s Enceladus. 

But their relevance to the biology of Astrophage, which thrives on the surface of the Sun, is probably limited. At 5,500 degrees Celsius, Astrophage’s preferred thermostat setting would cook any Earth life form in an instant.

Outer space ambassadors

If Astrophage weren’t draining Earth’s primary energy source, humanity might be celebrating its first encounter with alien life. If that were the case, I have no doubt tardigrades would be part of the welcoming party.

Also known as water bears and moss piglets, these microscopic, eight-legged animals are legendary for their ability to withstand extreme environments—including the final frontier. In 2007, tardigrades became the first animals to survive exposure to outer space over the course of a series of experiments aboard a Russian spacecraft. 

In one experiment, tardigrades were exposed to 10 days of hard vacuum. After they were brought back inside the craft, many reproduced normally. Tardigrades also fared well in a 2011 experiment aboard NASA’s Space Shuttle Endeavor, where neither microgravity nor cosmic radiation affected their survival. 

While scientists are still investigating how exactly tardigrades withstand exposure to outer space — in 2021, yet more water bears were sent to the International Space Station for a study of how spaceflight impacts their gene expression — a key factor is their ability to enter a state of ‘anhydrobiosis’. 

Essentially, when exposed to extremely dry conditions (including in space), tardigrades become a shrunken, shriveled husk and their metabolism slows to a crawl. 

Anhydrobiosis provides protection not just against drought, but extreme heat, radiation, and various chemicals. Apparently, some tardigrades can hang out in mummy-mode for years. 

That might not be long enough for them to traverse the vast distance between here and Tau Ceti (at least, not without an Astrophage-powered spacecraft). But if any Earth animal were to have a chance of colonizing another world, it would be the humble tardigrade. 

Heck, they’ve already taken over the Moon.

Of course, there are aspects of Astrophage’s biology that are truly out-of-this-world, like its ability to convert neutrinos into infrared light for propulsion. But while we may never face a foe quite like Project Hail Mary’s interstellar slime mold, there’s a good chance any alien encounters we do have will be with microoroganisms. It’s also not inconceivable that such bugs could pose a serious threat to us—or our entire planet.

In that case, the knowledge we’ve amassed about Earth’s most extreme life forms might be our best protection.

— Maddie