Water Worlds May Hide Water Underground

Combining two measurements taken for each of 43 exoplanets, scientists found the densities lower than expected, suggesting the presence of subsurface liquid.

IMAGE: A new study suggests that many more planets in distant solar systems have large amounts of water than previously thought — as much as half water and half rock. The catch? It’s probably imbedded underground, as in Jupiter’s moon Europa, above. CREDIT: NASA/JPL-Caltech/SETI Institute

While Mars is just one other world in our solar system that once had water — and still may have water underground — it’s not the only world with subsurface water. We’ve also found gravitational and magnetic evidence for subsurface water on a host of icy moons and dwarf planets, including Ganymede, Europa, Enceladus, and even Ceres and Pluto. Those discoveries alone have upped the possibility of exoplanetary worlds rich in water as well, and new research published in Science and led by Rafael Luque finds that we might even be looking for evidence of water on those exoplanets using the wrong hypothesis.

The team of researchers analyzed a population of planets found orbiting stars called M dwarfs or red dwarfs; they’re incredibly common stars, and we now have an extensive catalog of exoplanets in those types of systems. Since we cannot see the exoplanets themselves due to the relative brightness of their stars and their close-in orbits, we have to use the transit method to catch the dips in the light and the radial velocity method to calculate the gravitational tugs on the star. Co-author Enric…