Alien life might be able to eat cosmic shrapnel from dying stars
High-energy particles zipping through the cosmos are harmful to life on Earth, but scientists think it could be food for potential alien life elsewhere.
High-energy radiation is generally bad for life. It causes harmful mutations, cellular damage, and, in large doses, death. Yet a few special microbes on Earth can not only tolerate radiation but harness it as a food source—and life on other planets could survive on a similar diet.
A particularly dangerous type of radiation known as galactic cosmic rays can be found throughout space, and some faraway worlds are under constant barrage from these particles. Until now, most researchers would have considered this radiation detrimental to a healthy ecosystem. But a new study published July 28 in the International Journal of Astrobiology suggests that organisms evolving under constant galactic ray bombardment on other planets and moons might find a way to exploit the rays for energy. The prospect greatly expands the potential abodes for living creatures beyond Earth, allowing them to thrive far from the warmth of a star and conceivably even in the cold void of interstellar space.
“I love this paper,” says planetary scientist Sara Seager of the Massachusetts Institute of Technology, who was not involved in the work. “It puts all this stuff together about how high-energy radiation can be helpful, not just harmful. I thought that was extremely clever.”
(How much do cosmic rays affect us on Earth?)
Where do galactic cosmic rays come from?
When giant stars reach the end of their lives, the thermonuclear furnace in their cores goes critical and blows them to bits. Out of such spectacular supernovas stream charged particles like protons, which end up whizzing through the Milky Way. These charged particles—galactic cosmic rays—can have many billions of times the energy of the average photon or light particle emitted by the sun. Should cosmic rays hit your ordinary Earth organism, they would tear through its flesh like ultra-fast subatomic bullets.
Because cosmic rays carry an electromagnetic charge, our planet’s giant magnetic field deflects most of them. The rest smash into the upper atmosphere, where they strip molecules of their electrons and generate cascading chain reactions leading to showers of less-energetic particles. Thus, organisms on the Earth’s surface are mostly protected from galactic cosmic ray damage.
(How cosmic rays helped find a tunnel in Egypt's Great Pyramid.)
But on celestial bodies that lack a strong magnetosphere and have little to no atmosphere, like Mars or Jupiter’s icy moon Europa, cosmic rays will pummel right into the surface. Such radiation is often believed to sterilize such environments, but it’s not a huge stretch to imagine a slightly different outcome.
Turning cosmic radiation into food
Desulforudis audaxviator is a tiny microbe found in pools of water in a South African gold mine a couple kilometers underground. There, deep in the darkness, it survives on chemical byproducts produced when radioactive minerals in the surrounding rocks decay, a process known as radiolysis.
“You have this bug surrounded by radioactive rocks,” says astrobiologist Dimitra Atri of New York University Abu Dhabi, a co-author on the new study. “And that radioactivity basically cooks food for it.”
The scenario got Atri and his colleagues thinking about what would happen when galactic cosmic rays hit the surface of three alien environments: Mars, Europa, and Saturn’s moon Enceladus. Their computer simulations showed that the incoming radiation would generate cascades of particles much like they do in our upper atmosphere, releasing electrons that can be used as an energy source.
For instance, microbes belonging to the genus Geobacter can grow filaments that conduct electricity and allow them to capture electrons. The electron-eating bacteria Rhodopseudomonas palustris is similarly capable of harvesting electrons from minerals and metals for food.
Powered by such an energy source, the team calculated that potentially many thousands of microbes per centimeter could flourish at depths between half a meter and two meters below the surface of all three environments.
The idea has been well-received among other astronomers. “It’s important to think out of the box,” says planetary astrobiologist Abel Méndez, director of the Planetary Habitability Laboratory at the University of Puerto Rico who wasn’t part of the study. “I think this is something good to consider, especially for bodies that are far away, like Europa and Enceladus.”
What does this mean for the search for life?
The possibility that aliens might get their energy from cosmic rays greatly expands the range of the Habitable Zone—the region around a star where its heat can keep water liquid and provide energy for photosynthesis. Not only would distant icy moons be within a larger Radiolytic Habitable Zone, but also potentially rogue planets thrown out of their star systems or objects like asteroids that travel between stars since galactic cosmic rays are found throughout in the Milky Way.
“From [the microbes’] point of view, it's a great environment,” says Atri. “You're sitting just below the surface, and you have this constant radiation cooking food for you.”
While the new study is a chemical proof-of-concept, both Méndez and Seager caution that detecting cosmic-ray-feeding organisms from far away might be hard. These bugs would likely be living deep within rocks or ice and not necessarily producing any obvious signs of their existence. Atri agrees thinks that the best way to find such creatures would be to explore under the surface of another world.
Mars is our closest drilling option. Two robotic missions to the red planet set to launch in 2028 will carry drills large enough to search for biomolecules from underground microbes past or present: the European Space Agency’s Rosalind Franklin rover, which will analyze samples on Mars, and China’s Tianwen-3 mission, which should return samples to Earth in 2031. Both could help reveal whether cooking with cosmic rays is on the Martian menu.
(Are we alone in the universe? These Mars rocks could finally give us an answer.)
