These are two exoplanets orbiting a red dwarf star in a planetary system 218 light-years away in the constellation Lyra.

A team led by astronomers at the University of Montreal (Canada) has found evidence that two exoplanets orbiting a red dwarf star are “water worlds”, planets in which water makes up a large fraction of their volume. These worlds, located in a planetary system 218 light-years away in the constellation Lyra, do not resemble any planet in our solar system.

The team, led by PhD student Caroline Piaulet of the Université de Montréal’s Trottier Institute for Exoplanet Research (iREx), publishes a detailed study of the planetary system known as Kepler-138 in the journal Nature Astronomy.

Piaulet, who is part of Björn Benneke’s research team, observed the exoplanets Kepler-138c and Kepler-138d with the retired NASA Hubble and Spitzer Space Telescopes, and found that the planets -which are about once and a half the size of Earth–could be made largely of water. These planets and a closer planetary companion to the star, Kepler-138b, had previously been discovered by NASA’s Kepler space telescope. The water was not detected directly, but by comparing the sizes and masses of the planets with models, they concluded that a significant fraction of their volume — up to half — should be made up of materials that are lighter than rock but heavier than water. hydrogen or helium (which make up most of the gas giant planets like Jupiter). The most common of these candidate materials is water.

“We used to think that planets slightly larger than Earth were big balls of metal and rock, like scale versions of Earth, and that’s why we called them super-Earths,” Benneke explains. “However, we have now shown that these The two planets, Kepler-138c and d, are very different in nature: a large fraction of their entire volume is probably composed of water.This is the first time we have observed planets that can be confidently identified as water worlds, a type of planet whose existence was theorized by astronomers for a long time,”