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Exoplanets: Those water worlds would have sterile oceans too…

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artist’s concept of an ocean planet with two satellites/Lucianomendez (CC BY-SA 4.0)

A kind reader writes to tell us of recent research into the concept of ocean planets which brings up a little-noted problem:

It turns out that water worlds may be some of the worst places to look for living things. One study presented at the meeting shows how a planet covered in oceans could be starved of phosphorus, a nutrient without which earthly life cannot thrive. Other work concludes that a planet swamped in even deeper water would be geologically dead, lacking any of the planetary processes that nurture life on Earth…

“We have this stereotype that if we have oceans, we have life,” says Tessa Fisher, a microbial ecologist at Arizona State. But her recent work contradicts this idea. Fisher and her colleagues studied what would happen on an “aqua planet” with a surface that is almost or completely covered by enough water to fill Earth’s oceans five times.

On Earth, rainwater hitting rocks washes phosphorus and other nutrients into the oceans. But without any exposed land, there is no way for phosphorus to enrich water on an aqua planet over time, Fisher reported at the Laramie meeting. There would be no ocean organisms, such as plankton, to build up oxygen in the planet’s atmosphere, she says — making this type of world a terrible place to find life. Alexandra Witze, “Exoplanet hunters rethink search for alien life” at Nature

Rats. An ocean planet seemed such a great idea in principle.

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See also: Recent finding: The “water world” exoplanets are NOT habitable ocean planets So, it turns out, even if there IS lots of water in a solar system, that doesn’t add up to habitability either. Talk about Rare Earth and Privileged Planet.

One Reply to “Exoplanets: Those water worlds would have sterile oceans too…

  1. 1
    vmahuna says:

    “rainwater hitting rocks washes phosphorus and other nutrients into the oceans. But without any exposed land, there is no way for phosphorus to enrich water”
    Um, if you IMMERSE those same rocks in water they will NOT partially dissolve?? That seems strange. What if we heat the underwater rocks to 1,000 degrees F? Won’t be get liquid iron?
    But my understanding is that lack of active tectonic plates would be a SERIOUS problem, with or without water. Venus lacks tectonic plates and this prevents the planet’s surface from renewing itself. All that deadly overheated Venusian acid atmosphere simply fights an eternal battle against the original surface.

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