A recent study challenges the conventional understanding of the 'habitable zone' around stars, suggesting that liquid water may exist on planets previously considered too hot or too cold for it. The research, conducted by astrophysicist Amri Wandel of Hebrew University in Jerusalem, expands the potential range for planets that could harbor extraterrestrial life.
The traditional habitable zone defines a narrow orbital distance from a star where conditions are suitable for liquid water to exist on a planet's surface. This new study argues that this 'Goldilocks' model is overly restrictive, particularly for planets orbiting smaller, cooler M-dwarf and K-dwarf stars.
Key findings indicate that tidally locked planets, which perpetually show one face to their star, could sustain liquid water on their eternally dark side. Heat from the sunlit hemisphere can transfer sufficiently to warm the dark side, allowing water to remain liquid even on planets closer to their stars than previously modeled. This could explain recent observations by the James Webb Space Telescope of water vapor on 'super-Earths' orbiting M-dwarf stars, which earlier models deemed too close for water survival.
Furthermore, the study suggests that the habitable zone extends farther from stars. On cold, distant planets, liquid water might exist in subglacial lakes or melt pockets beneath thick ice, similar to conditions found on some moons within our solar system.
By broadening the criteria for where liquid water can exist, this research significantly expands the potential pool of planets that astronomers could investigate for signs of life, implying that the conditions necessary for life might be more prevalent across the universe.