The team, led by Caroline Piaulet, a Ph.D. student of the Trottier Institute for Research on Exoplanets (iREx) at the Université de Montréal, published a detailed study of the Kepler-138 planetary system. The study, titled Evidence for the volatile-rich composition of a 1.5-Earth-radius planet, was published in the journal Nature Astronomy today.

Piaulet used data from NASA's Hubble and Spitzer space telescopes to analyse the composition of exoplanets Kepler-138 c and Kepler-138 d and discovered that the planets as a whole must be composed largely of water.

"We previously thought that planets that were a bit larger than Earth were big balls of metal and rock, like scaled-up versions of Earth, and that’s why we called them super-Earths" explains Björn Benneke, a co-author on the paper. “But this is not the case for these two planets, for which we have found that up to half of their volume is likely to be water,” adds Diana Dragomir, an assistant professor in the Department of Physics and Astronomy at The University of New Mexico and co-author on the study. “These planets are unlike any planets in our Solar System. The closest comparison would be some of the icy moons in the outer Solar System that are also composed of water to a large fraction, with rock found only in the deep interior.”

Read more at UNM Newsroom.