The traditional astrophysical recipe for life as we know it is quite simple: Get a rocky, gas-shrouded world in a “habitable zone” orbit around a star so that it’s not too hot or too cold. Then just add liquid water to its surface and let the primordial soup simmer for millions of years as energy from starlight gradually cooks up the chemical building blocks of life.

 But astrophysicists have come to realize this classical habitable zone scenario may overlook opportunities for life farther out from a star. After all, Saturn’s moon Enceladus, Jupiter’s moon Europa and even Mars are known or believed to harbor vast amounts of water in their dark interior. Life on these worlds would have to lurk underground for reasons other than thirst alone because their surface is scarcely shielded by an atmosphere and constantly bombarded with lethal cosmic rays.

A recent study, however, supports the idea that, in such places, cosmic rays can actually benefit life belowground rather than just banishing it from the surface. Led by Dimitra Atri, a researcher at New York University Abu Dhabi, the study team has introduced the concept of a “radiolytic habitable zone,” a region within a world where the energy unleashed by cosmic rays is enough to sustain life. Published in the International Journal of Astrobiology, the study provides a new framework for calculating how much living matter could be supported at various depths inside Mars, Europa, Enceladus and similar places well outside the standard, starlight-based habitable zone.

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