Are Water Worlds Really the Best Places to Look For Alien Life?

Fagjun | Published 2017-11-30 17:13

Researchers think that planets covered with water may not be the best candidates for the search for extraterrestrial life.

Can water-covered planets sustain life?



There’s one thing that has guided the search for life on other planets, and it’s the thought that the presence of water increases the likelihood that a planet may host life. After all, models based on our own planet stress the significance of water on the development of lifeforms. If life as we know it exists on other planets, then they’re likely to exist on planets with water. Thus, planets that have liquid water are thrust at the forefront of the search for life beyond Earth.


However, a new study now suggests that water worlds--planets covered with water--may not actually be capable of supporting life. This is because though water is an important ingredient for life, it’s not the only one we should consider. Researcher Tessa Fisher and her colleagues have found that a planet covered with water may be missing one key component found in life forms.

A Vital Ingredient

The presence of land on the surface may be important to the development of life forms.



Phosphorus is an important ingredient found in DNA, as well as other important molecules. Without phosphorus, life on Earth would not be able to thrive. However, phosphorus is not as easily available or accessible as other nutrients that support life. On Earth, phosphorus is mainly found in rocks, washed away to the oceans by rainfall. Phosphorus then helps microbes in the water thrive.


So envision a planet covered with water. Before Fisher pointed out this little hiccup over the presence of phosphorus, we would have thought that the water-covered planet would be a prime candidate for the search for extraterrestrial life. However, without exposed lands on the planet’s surface, there would be a lot less phosphorus available for any form of life that’s beginning to thrive in the waters. The researchers estimate that a water world such as this would have about three to four times less phosphorus than Earth’s oceans.


Thus, even just having life thrive in those theoretical waters would be kind of a stretch. However, if life did somehow manage to gain a foothold in that water world, it would actually be difficult to find. It’s possible that even if microscopic life managed to exist on such a planet, they would probably release undetectable amounts of oxygen. So if they’re there, we might not know it.


Fisher and her team presented their study at the Habitable Worlds conference in Laramie, Wyoming. It was at that conference that several scientists concluded that there may be a need to reconsider the parameters by which we evaluate a planet to possibly be habitable. They think that we shouldn’t automatically consider a planet covered in water to be a candidate for the search for life. Instead, scientists should focus on how the planets evolved over time

Goodbye, Water Worlds


Kepler 22b may be a water world covered by a so-called "super ocean". [Photo by NASA/JPL-Caltech]



“We have to also think about the other things that impact not just whether life could get a foothold but also how productive that life would be,” said Goddard Space Flight Center’s Shawn Domagal-Goldman, who had attended the conference. “Because if a planet is in a habitable zone, even if it has life, we may not be able to find that life.”


Water worlds are actually quite easy to find. This is because a lot of planets likely formed away from their host star, thus forming with an icy surface. However, as the planets drew closer to their star, the ice on their surface melted. Some of the planets orbiting the nearby star TRAPPIST-1 may actually have surface predominantly covered with water.


Given Fisher and her team’s findings, however, if we want to find extraterrestrial life, we’d have to look a little harder.

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