Exoplanets come in a variety of types, and so-called “water worlds”—planets with at least ten percent of their total mass consisting of water, and no land exposed to the atmosphere—appear to be among the most common. At last week’s Goldschmidt Conference in Boston, Li Zeng from Harvard University and co-authors claimed, based on their modeling of the evolution and growth of planets, that exoplanets with diameters about two to four times greater than Earth’s are likely to have surfaces covered by oceans, rather than being a mix of land and water as on our own planet.
While those super-Earth water worlds are probably uninhabitable due to very high surface temperature, smaller, cooler water worlds could be habitable, according to another recent paper by Ramses Ramirez from the Tokyo Institute of Technology and Amit Levi from the Harvard-Smithsonian Center for Astrophysics. They point out that subpolar sea ice may enhance the habitability of water worlds by moderating their climate.
This begs the question: Assuming life can originate on a water world, say, at a hydrothermal vent at the bottom of the ocean, how far could it evolve? Could we expect intelligent life, or even technologically advanced life, on a world with no exposed land area?