Life may be able to survive beneath the surface of Mars and other planets because of energy generated by cosmic rays, researchers from the New York University Abu Dhabi (NYUAD) have found.
The new study, published in the International Journal of Astrobiology on July 28, suggests that future missions looking for microscopic life may need to dig deeper into the surface.
Dr Dimitra Atri, principal investigator at NYUAD’s space exploration laboratory and lead author of the study, told The National that underground regions where cosmic radiation can trigger chemical reactions may be more promising, instead of surface environments warmed by sunlight.
“For decades, most of our ideas about where life might thrive beyond Earth have revolved around sunlight or heat from a planet’s interior,” he said.
“But there are places in our solar system, like Mars, Europa (one of Jupiter’s moons), and Enceladus (a moon of Saturn) where there just isn’t enough sunlight or geothermal heat. It made me ask: could there be another way for life to get energy in these dark, cold places?”
How the study worked
The study explores how high-energy particles from space, known as cosmic rays, can penetrate below the surface of planetary bodies with thin or no atmospheres, such as Mars and the icy moons. When cosmic rays interact with underground water or ice, they can break apart water molecules in a process called radiolysis, producing energy-rich compounds like hydrogen.
“We have learnt from Earth that some microbes deep underground, cut off from sunlight, can survive using energy from the natural breakdown of radioactive minerals in rocks,” said Dr Atri.
“This process, called radiolysis, splits water molecules and produces chemicals like hydrogen gas, which some bacteria can use. It is not just theory, this is something we have observed in places like deep South African gold mines.”
How does the study change our understanding?
For decades, habitability was thought to be limited to planets within the "Goldilocks Zone", the region around a star where temperatures are just right for liquid water to exist on the surface.
But this new study introduces a different concept: the Radiolytic Habitable Zone (RHZ), an underground region where cosmic rays could generate enough energy to support microbial life without being too damaging. It suggests that life may also thrive in cold, sunless environments deep beneath the surface.
“The big idea was … could cosmic ray-induced radiolysis carve out a 'habitable zone' beneath the surfaces of these worlds, providing a steady and reliable energy source for microbes?” said Dr Atri.
The research focused on Mars, Europa and Enceladus, which are all known to have ice or possible liquid water under their surfaces. The computer simulations showed that Enceladus had the most potential to support life in this way, followed by Mars and then Europa.
Dr Atri said this work should influence how scientists design future space missions and where they target their life-detection instruments.
“If we take radiolysis seriously, we need to design missions that can drill or sense a few metres below the surface, not just scratch the top layer,” he said. “Instruments would need to look for chemical signatures of radiolysis, like certain gases or organic molecules linked to microbial life powered by this process.
“It also means focusing on places with thinner ice or rock where cosmic rays can penetrate and water might be present, say, fissures on Enceladus, cracks in Europa's ice, or subsurface layers on Mars.” He said that if mission planners ignore the effects of cosmic rays and radiolysis, they “could miss the promising habitats in the solar system”.
How will the findings shape future missions?
Most Mars missions so far have focused on the surface, but newer ones are looking to dig deeper for signs of underground life. The European Space Agency’s Rosalind Franklin rover, now set to launch in 2028 after multiple delays, will carry a drill that can dig two metres below the surface to search for signs of life.
Nasa’s Perseverance rover has been collecting soil and rock samples from the Jezero Crater on Mars since 2021, although it drills only shallow depths. The study is also interesting because cosmic rays are typically seen as harmful, especially for humans, but this research argues that high-energy particles could be a source of energy for life underground.
“Cosmic rays are definitely a double-edged sword. They damage DNA, disrupt cell function, and, at the surface, are a big problem for both life and future astronauts,” said Dr Atri. “That’s why Earth's magnetic field and atmosphere are so important, they shield us from most of this radiation.
“But when cosmic rays hit water or ice underground, they trigger radiolysis, breaking apart water molecules and producing energy-rich compounds that some microbes could use. So, while life on the exposed surface would be at risk, microbes just the right distance below, shielded from the worst of the radiation but still close enough to get radiolysis by-products, could actually benefit.”
