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Although water worlds are awash with one of the key ingredients for life, surprisingly, they might not be the best places to find it.

Tessa Fisher, a graduate student at Arizona State University in Tempe, and her colleagues presented this counter-intuitive idea last week at the Habitable Worlds conference in Laramie, Wyoming. Her research shows that a planet soaked in oceans could be starved of phosphorus – a major component of DNA and other important molecules.

Unlike other essential nutrients for life, phosphorous is hard to find. It’s mostly locked away in rocks, so it only becomes accessible when rainfall splatters those rocks and flushes phosphorous into water where it can be used by microbes.

Although rainwater is quite efficient at dissolving phosphorus, seawater is not. And that’s a problem for worlds entirely covered by salty seas. Without any exposed land, there will be far less phosphorous available for fledgling life. Fisher and her colleagues have estimated that these worlds will have three to four times less phosphorous in their oceans than seas on Earth.

Not only does Fisher’s work suggest that kick-starting life on such a world would be tricky, it is also possible that should life take hold, astronomers would be hard-pressed to detect it. In fact, Fisher and her colleagues found that even if life such as phytoplankton is present, they would release only one-tenth the amount of oxygen currently in Earth’s atmosphere. That’s far too low to be detectable.

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Category: Science