Hubble telescope reveals 'water worlds' in nearby star system

Data from the Hubble space telescope has revealed what scientists say are likely two ocean-covered planets in a star system relatively close to our Solar System. 

The planets, dubbed Kepler-138 c and Kepler-138 d, were examined using data from both Hubble and NASA's Spitzer Space Telescope.

The European Space Angecy said in a release that though "water wasn’t directly detected" from available data, "by comparing the sizes and masses of the planets to models," scientists were able to determine that "a significant fraction" of the volume of the planets "should be made of materials that are lighter than rock but heavier than hydrogen or helium."

"The most common candidate material is water," the ESA said. 

University of Montreal astronomer Björn Benneke said the data present "the best evidence yet for water worlds."

Such words, Benneke said, are "a type of planet that was theorised by astronomers to exist for a long time.”