Water worlds could be more common than we think.
It’s only been a few decades since astronomers have been able to confirm the existence of planets around other stars beyond our solar system, and we’re really just getting the tools online to start checking those distant worlds for signs of life.
A big presumption in this most important of all searches is that other Earth-like planets are probably the best type of exoplanets focus on, but new research supports broadening the search.
A team of researchers from Switzerland used computer models to determine that liquid water could exist on planets very different from Earth for long periods of time, up to tens of billions of years, even.
“One of the reasons that water can be liquid on Earth is its atmosphere,” Ravit Helled from the University of Zurich explains in a statement. “With its natural greenhouse effect, it traps just the right amount of heat to create the right conditions for oceans, rivers and rain.”
But other, more primordial atmospheres consisting of mostly hydrogen and helium, which Earth had early in its development, can also induce a greenhouse effect and the models showed they can also maintain liquid water.
Some planets with geothermal activity may even be able to maintain liquid water on the surface without much help from the radiating energy of a nearby star.
“To many, this may come as a surprise,” Christoph Mordasini from the University of Bern explains. “Astronomers typically expect liquid water to occur in regions around stars that receive just the right amount of radiation: not too much, so that the water does not evaporate, and not too little, so that it does not all freeze.”
Helled and Mordasini are co-authors on a new paper in Nature Astronomy, along with Marit Mol Lous.
The bottom line is that it might not have to be a Goldilocks sort of situation for liquid water to exist on other worlds, which points to a big question: If that’s the case, then do conditions have to be just right on other planets for life to emerge?
“Since the availability of liquid water is a likely prerequisite for life, and life probably took many millions of years to emerge on Earth, this could greatly expand the horizon for the search for alien lifeforms. Based on our results, it could even emerge on so-called free-floating planets, that do not orbit around a star,” Mordasini adds.
Of course, liquid water over the long haul isn’t necessarily enough to support life, he cautions.
“Even under the right conditions, it is unclear how likely it is for life to emerge in such an exotic potential habitat. That is a question for astrobiologists. Still, with our work we showed that our Earth-centered idea of a life-friendly planet might be too narrow.”
