Water is abundant on many small extrasolar planets, but it does not flow in oceans and rivers like it does on Earth.
More planets than previously thought may have large amounts of water.
The Canary Islands Astrophysics Department examined the radius and mass of 43 known small exoplanets orbiting an M-dwarf star.
These are the most common stars in our galaxy, and scientists have discovered dozens of planets orbiting them in recent years.
Because stars are much brighter than their planets, we cannot see the planets themselves.
Scientists have used this data to compare alien worlds to our solar system's planets.
The researchers believe that water may exist in the rock or in pockets beneath the surface.