In this week’s episode, I returned to the ongoing segment about Fermi’s Paradox (“Where is Everybody?”), which focuses on another proposed resolution known as the Waterworlds Hypothesis. Basically, this theory takes the traditional “follow the water” and asks the question: could rocky exoplanets orbiting distant stars have too much water to be habitable? This theory is based on the current exoplanet census, which indicates that there are many rocky planets several times the size and mass of Earth but with lower densities.
This suggests that volatile elements (such as water) make up a significant fraction of these planets’ mass. If true, this would indicate that these rocky worlds are completely covered in deep oceans. If they don’t possess a dense atmosphere, they would likely consist of an icy outer shell, an interior ocean, and a rocky and metallic core. This is similar to what we see in our own Solar System, where many satellites orbiting the gas giants are thought to have interior oceans beneath their icy crusts.
Like Jupiter’s moon Ganymede, the depths and pressure conditions in these oceans would lead to the formation of an ice layer between the ocean and the rocky, metallic core. If true, this would mean that the very things that could support the emergence of life – hydrothermal activity at the core-mantle boundary – would be missing. Based on the fossil record, this is how scientists believe life emerged on Earth (around deep-sea vents) and what is believed to be happening inside Jupiter’s moon Europa.
However, this does not mean that all Waterworlds can’t support life. In fact, there’s also research that indicates that planets lacking continents and plate tectonics could still support life, perhaps in the form of “space whales“! Still, using Earth as a template, the lack of continents and land masses could mean that evolution would be restricted, and tool-using species may not emerge. So it begs the question: If rocky planets with too much water are the norm, and Earth is an outlier, could this be why we haven’t heard from any extraterrestrial civilizations yet?
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Stories by Williams 