Are Water Worlds Habitable?

Apr 5, 2018

By Shannon Hall

Roughly 39 light-years away toward the constellation Aquarius is a planet that hosts a global ocean so deep it drowns the land. Set sail anywhere on that water world and you will never spot mountains, hills or even beaches on the horizon, just deep blue tides. And this planet is not alone. A new analysis of the exoplanets circling TRAPPIST-1—which a 2017 study estimated were all roughly the size, mass and composition of Earth—suggests that four of the seven worlds are actually soaked in water. Two of them are more than 50 percent water, by mass, and the other two are less than 15 percent (that is still far wetter than Earth, which is less than 0.1 percent water). What is more: Multiple lines of evidence suggest that water worlds might be abundant throughout the cosmos.

That might sound like good news. After all, wherever we find water on Earth—be it the acidic pools of Yellowstone or the cracks within frozen glaciers—we find life. The correlation is so strong that NASA has adopted the mantra “follow the water” when searching for life beyond our pale blue dot. But these wet worlds have sparked a lively debate about how much water is too much.

Take the fifth planet within the TRAPPIST-1 system as an example. Cayman Unterborn, an exogeologist at Arizona State University in Tempe, and his colleagues think that the liquid water here extends down about 200 kilometers—roughly 20 times deeper than Earth’s Mariana Trench. That much water would create a large ice layer at the bottom of the ocean which would seal the ocean from the land and effectively shut down a geochemical cycle that plays a crucial role in Earth’s habitability.

Continue reading by clicking the name of the source below.

One comment on “Are Water Worlds Habitable?”

  • @OP Take the fifth planet within the TRAPPIST-1 system as an example.

    This is essentially an academic issue which is likely to be of little importance to humans.

    Cayman Unterborn, an exogeologist at Arizona State University in Tempe, and his colleagues think that the liquid water here extends down about 200 kilometers—roughly 20 times deeper than Earth’s Mariana Trench.

    Any life which evolved on a planet totally covered by water would be aquatic, which largely excludes technologies and space travel.
    It would be extremely difficult to develop rockets, and any habitation capsules would have to contain water, which is massively heavier than air!

    Such planets would also be unlikely choices for human habitation – given the need for access to materials and industry to produce floating bases.

    That much water would create a large ice layer at the bottom of the ocean

    That would very much depend on temperatures and geological activity.

    which would seal the ocean from the land and effectively shut down a geochemical cycle that plays a crucial role in Earth’s habitability.

    Even without a seal of sea-floor ice, given that many planets are tidally locked, they could well be lacking tidal activity stirring up minerals in the water or setting up Earth-type weather or erosion cycles. Mineral erupted injections in to oceans if any, would be volcanic where volcanism persisted long enough for life to evolve!

    With no land to disrupt water or air flows, any planet which was totally covered by water and meteorologically active, would probably have violent storm systems perpetually circulating around its entire globe, as is the case with Jupiter and other gas/ice giants.



    Report abuse

Leave a Reply

View our comment policy.