Two exoplanets (planets located outside our solar system) composed essentially of water would have been discovered in the constellation of Lyra, 218 light-years away from the Earth.
Kepler-138 c and Kepler-138-d, together, are larger than the Earth, but less dense than the latter. For proof, they have a mass of twice that of the Earth and a volume equivalent to three times that of the blue planet.
Like the Earth, their core is composed of metals and rocks. However, their external envelope is covered with water molecules in the form of a thick layer of water (2000 km) at high pressure overhung by a thick layer of water vapor.
The discovery was made by researchers from the Trottier Institute for Exoplanet Research at the Université de Montréal.
More details on the Université de Montréal news site » [in French]
