Life beyond Earth may be more common than thought
Life beyond Earth may exist in far stranger places than scientists once thought, a new study suggests. Worlds previously thought to be too hot, too cold, or permanently dark could still harbor liquid water, the key ingredient for life.
For decades, astronomers have searched for planets in the “habitable zone,” a narrow ring around a star where temperatures allow water to remain liquid. Within the solar system, the habitable zone extends approximately from Earth’s orbit to the orbit of Mars. However, many currently discovered exoplanets do not fit perfectly into this framework.
Some stars orbit very differently from the sun, while others lie much closer or further from their star than the traditional habitable zone allows.
A new study by Professor Amri Wandel, an astrophysicist at the Hebrew University, questions the assumptions behind this classic definition. Published in the peer-reviewed journal The Astrophysical Journal, the research focuses on tidally locked planets, worlds that always show the same face to their star.
One side experiences permanent daylight, while the other remains in eternal night. Until now, the dark side was believed to be frozen, making it unlikely to support water or life.
Wandel’s analysis suggests otherwise. Using a model that tracks temperatures on a tidally locked planet, the study reveals that heat from the day side can flow to the night side, keeping some regions warm enough for liquid water. This could happen even on planets orbiting very close to cooler stars, such as the M and K dwarfs, previously thought to be too hot for surface waters.
Water may exist on the dark side of tidally locked planets
“Our results show that liquid water can exist on the dark side of tidally locked planets,” Wandel said. “This expands the environments in which conditions favorable for life can exist, well beyond what the traditional habitable zone predicts.”
The research also extends the habitable area outwards. On planets far from their stars, once thought to be too cold, liquid water could survive under thick ice sheets in subglacial or intraglacial lakes.
“Planets that appear frozen on the surface could be hiding liquid water underneath,” Wandel explained. “These hidden reservoirs could provide potential habitats for life, greatly increasing the number of worlds worth exploring.”
The results also help make sense of recent observations from the James Webb Space Telescope, which detected water vapor and other gases in the atmospheres of hot, nearby super-Earths orbiting M dwarf stars, planets previously thought to be outside the safe range for water.
By questioning ancient rules governing conditions favorable to life, Wandel’s study reframes the search for habitable worlds. “The universe may be much more accommodating to life than we imagined,” he said.
Planets once considered too extreme, too hot, too cold, or facing permanent darkness may now be considered promising candidates in the hunt for life beyond the solar system. As astronomers continue to explore distant worlds, the results suggest that the cosmic map of potential habitats may be much larger than previously thought.
The results could help astronomers focus their search for life by identifying planets that were previously thought to be too hot, too cold or permanently dark. By refining models of global climates, the study provides a clearer picture of how heat and water might behave on these unusual worlds, improving predictions about which planets might support life. The study could also shed new light on extreme climate dynamics on Earth.
