Habitability: Just Add Water: A Lot of It
Desert planets are likely
unlivable, even if they have
water. They need oceans of it.
Imagining life on other planets was too easy back in Carl Sagan’s day. Put a planet into an orbit with a continuous temperature between 0 and 100 degrees Celsius, just add water, and presto! Evolution would take care of everything. Since then, the list of factors required to support life on a planet or moon has grown. In his book Spacecraft Earth, contributing author Dr Henry Richter listed 15 requirements for a planet to host life (p. 29). Multiplied together, the probabilities of meeting those needs would make life uncommon in the universe. Now we can add another requirement.

AI images generated by Grok
Desert planets like those in ‘Dune’ and ‘Star Wars’ unlikely to host life, NASA says (6 Jan 2025, Space.com). In this article about a presentation by the AGU (American Geophysical Union), Tom Brown relates what an upcoming paper by NASA scientists will argue: planets need large amounts of water to be habitable.
The science team with NASA’s Habitable Worlds Observatory project, which is aimed at looking for signs of alien life in distant solar systems, suggested that planets considered habitable are likely to need water on their surface for the classic reasons — but also for some you may not expect. For example, the team discovered that water plays a key role in stopping a planet’s temperature from fluctuating. Life on Earth generally requires a relatively stable temperature in order to survive, so that’d likely be the case on other worlds if the life that exists there is similar to life as we know it.
Earth’s oceans have enough water to stabilize the global temperature, but desert worlds like some portrayed in movies would likely be out of luck.
“These arid, dry planets, with significantly less than one Earth’s ocean of water may be common throughout the universe,” Haskelle Trigue White-Gianella, a Ph.D. student at the University of Washington who ran computer simulations tracking the evolution of desert planets, said during the talk. “We found that there is a threshold of water needed to maintain a stable climate … Even if a planet is in the habitable zone, if it has too small a water inventory, it transitions to an uninhabitable state.”
Brown relates a threshold number of surface water coverage, about 10%, that is was discussed as a probable minimum for a planet to sustain life. Below that threshold, runaway heating could eliminate a planet’s lakes and oceans, rendering it like Venus—even if it were in the so-called CHZ (Continuously Habitable Zone).
The article mentions evolution 10 times. The researchers think that if life evolved on such a planet, it would likely die out when the water was all gone.
The required minimum of water, it should be noted, must be on the surface, not in underground reservoirs. Only from the surface could water regulate the global temperature in contact with the planet’s atmosphere. Surface water can also form rain clouds to cool its continents, Brown says.
If desert planets are common, like White-Gianella stated, then only a few of them would qualify as habitable. The new analysis could ruin some movies like Star Wars and Dune that portray complex intelligent beings on desert planets.
It must be hard being an astrobiologist. Those in NASA’s Bio-Astrology Program (our name for it) were already taking a beating trying to get a cell to emerge from chemicals, and now this. The true believers will just move their imaginary zoos into dark underground oceans that might be warm enough to evolve organisms without an atmosphere, and where no scientist or space telescope will be able to observe them.
Don’t get lost in the fogma of Darwin Fantasyland. Get Spacecraft Earth for more realism about the requirements for life. Click the image to order.

Dr Richter’s book examines many amazing examples of design in our bodies, our planet, and the universe.