Science and Exploration

Cosmic Water Studies Are Expanding the Notion of Planetary Habitability

By Jon Kelvey
August 31, 2023
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Cosmic Water Studies Are Expanding the Notion of Planetary Habitability
Illustration showing the relative size of the exoplanets in the TRAPPIST-1 planetary system.
Image credit: NASA/JPL-Caltech.

Water is essential to life as we know it, and therefore water’s presence, or absence, and the ways in which we can detect it in the universe, are major components of the larger scientific project of studying the cosmos for signs of alien life.

In fact, the concept of a habitable or “Goldilocks” zone, is based on the range of orbits around a given star where an exoplanet may be expected to sustain liquid water on its surface. Earth sits right in the middle of our Sun’s habitable zone, with Venus and Mars taking up the extreme edges. But new discoveries have shown the habitable zone to be a simple heuristic when searching for the elements necessary for life, not a hard fast rule. In our own solar system, for instance, scientists now believe the icy moons of Jupiter and Saturn, such as Europa and Enceladus, may hold conditions favorable for life in subsurface liquid water oceans. The concept of the habitable zone is itself expanding.


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Jon Kelvey

Jon Kelvey is a science writer covering space, aerospace, and biosciences. His work has appeared in publications such as Air & Space Magazine, Earth and Space News, Slate, and Smithsonian in addition to SpaceRef.