Desert planets might be the more common type of habitable planet in the galaxy

Picture the planet from the books and movie titled "Dune."

(PHYSORG)- Desert planets strikingly like the world depicted in the science fiction classic "Dune" might be the more common type of habitable planet in the galaxy, rather than watery planets such as Earth, researchers suggest.

Their findings also hint that Venus might have been a habitable desert world as recently as 1 billion years ago.

Nearly everywhere there is water on Earth, there is life. As such, the search for life elsewhere in the universe has largely focused on "aqua planets" with a lot of liquid water on their surfaces — either terrestrial planets largely covered with oceans, such as Earth, or theoretical "ocean planets" completely covered by a layer of water hundreds of miles deep, somewhat like thawed versions of Jupiter's moon Ganymede.

To be habitable, aqua planets must orbit their stars in a so-called "Goldilocks zone" where they are neither too hot nor too cold. If they are too far from the Sun, they freeze; if they are too close, steam builds up in their atmospheres, trapping heat that vaporizes still more water, leading to a runaway greenhouse effect that boils all the oceans off the planet, as apparently happened on Venus. Eventually, such planets get so hot, they force water vapor high enough into the atmosphere for it to get split into hydrogen and oxygen by ultraviolet light — the hydrogen then escapes into space, the oxygen likely reacts with the molten surface and gets incorporated into the mantle , and the planet's atmosphere loses all its water over time.

Instead of aqua planets with abundant water on their surfaces, researchers investigated what "land planets" might be like, ones with no oceans and vast dry deserts, but perhaps oases here and there. The planet Arrakis depicted in science fiction classic "Dune" is one exceptionally well-developed example of a habitable land planet, said planetologist Kevin Zahnle at NASA Ames Research Center. Arrakis is essentially a bigger, warmer, sparsely inhabited version of Mars with a breathable oxygen atmosphere and polar regions cool and moist enough to have small water icecaps and morning dew.