A new evaluation of data from the exoplanet-hunting Kepler Space Telescope and the Gaia mission indicates that many of the known planets may contain as much as 50% water. This is much more than the Earth's 0.02% (by weight) water content.
So there is a lot of water in the universe and many planets with deep oceans. To understand the next bit, remember that Kepler mostly found planets that were big and orbiting close to their stars. This study identified two groups of planets, one with diameters about 1.5 times that of earth, which are mostly rock, and another with a diameter about 2.5 times that of earth. Those larger planets are, this study says, made up largely of water. But they're very weird by our standards:
"This is water, but not as commonly found here on Earth," said Li Zeng. "Their surface temperature is expected to be in the 200 to 500 degree Celsius range. Their surface may be shrouded in a water-vapor-dominated atmosphere, with a liquid water layer underneath. Moving deeper, one would expect to find this water transforms into high-pressure ices before we reaching the solid rocky core. The beauty of the model is that it explains just how composition relates to the known facts about these planets."
Li Zeng continued, "Our data indicate that about 35% of all known exoplanets which are bigger than Earth should be water-rich. These water worlds likely formed in similar ways to the giant planet cores (Jupiter, Saturn, Uranus, Neptune) which we find in our own solar system. The newly-launched TESS mission will find many more of them, with the help of ground-based spectroscopic follow-ups."
Again, Kepler's planets are mostly large, hot worlds orbiting close to their suns, so nothing says there aren't plenty of smaller, cooler water planets out there. But this study is still a nice indication of how weird the universe it, and good we are getting at learning about it.
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