Water is abundant on many small exoplanets, but according to a study led by the University of Chicago and the Spanish, it doesn’t flow in oceans and rivers as it does on Earth, but is likely buried in rocks or pockets below the surface. Institute of Astrophysics of the Canary Islands (IAC).

A study published Thursday in the journal Science and this suggests abundant populations of water and rock exoplanets around the M-dwarf stars most common in the Milky Way.

For this study, led by researchers Rafael Luque from the University of Chicago and the Andalusian Institute for Astrophysics (IAA-CSIC) in southern Spain, and Enric Pallé of IAC and La Laguna University (ULL), the Spanish Atlantic archipelago is located in the Milky Way with 80% of the stars. The radii and mass of 43 known small exoplanets around M dwarf stars representing the .

Rafael Luque explains in his statement that they have discovered the first experimental evidence that water worlds exist as a population, and that they are in fact almost as abundant as the terrestrial planets.

Many more planets than previously thought could contain large amounts of water, which makes up 50% of the planet’s total mass, according to the study.

Enric Pallé told Efe that half of these planets are water, so the amount is huge and if it were in the form of an ocean it would be thousands of kilometers deep, but the data shows that the most superficial layer is melting and the most superficial layer of the earth is melting. water below and above the core.

He added that there will be liquid water at some point and it is not known whether there will be life, but that the vast majority of planets are known to be equal in composition to Earth, so the chances of finding life increase greatly. this reason.

When the researchers analyzed the sample, they found something unexpected, because the densities of a large percentage of the planets indicated that they were too light for their size to be composed of rock alone.

Therefore, they believe these planets must be composed of half rock half water or some other lighter molecule, and they discovered that what separates the planets is not the radius, as previously thought, but the density of the planet. wet, commented Rafael Luque.

However, these planets are so close to their suns that any surface water will be in a supercritical gas phase, increasing their size.

Therefore, the scientists think that in this type of population, the water would likely be buried in rock or in pockets below the surface, rather than flowing like oceans or rivers.

These conditions would be similar to those of Jupiter’s moon Europa, but very different from those that occur on Earth, a “dry” planet that gives it a very dry appearance even though nearly all of the water is on the surface. . Earth’s water is only 0.02% of its total mass, while in water worlds it is 50% of the planet’s mass”, Enric Pallé stated.

He added that they discovered that minor planets around these stars could be identified by a distinct family population: planets very much like Earth, planets that are 50% of their mass in water (water worlds or “water worlds”), and mini-Neptunes with expanded atmospheres of hydrogen and/or helium. .

This finding contradicts the general notion that these worlds are either dry and rocky or have a large and thin atmosphere of hydrogen and/or helium.

And instead, he suggests that unlike rocky planets, these water-rich worlds form outside the so-called “snow line,” at a distance where the temperature is low enough to allow lighter compounds such as water to solidify and form. solid ice grains then migrate inward.

Palle noted that the distribution of sizes and densities of exoplanets is a direct result of the formation of planets at different distances from the star, not the presence or absence of an atmosphere.

The researchers explain that in the same way that observing the population of an entire city can reveal trends that are hard to see individually, studying a planet’s population helps identify hitherto unknown patterns.

“Due to errors in the mass and radius of our measurements, a single planet can sometimes fit into different categories (terrestrial, ‘water worlds’…). different compositional patterns”, Luque pointed out.

According to the researchers, the next steps will be to understand the internal structure of the water worlds, namely where water is stored and whether these planets could host a small, detectable atmosphere of supercritical water vapor.

Enric Pallé said that only planets around M stars in the habitable zone are accessible for atmospheric exploration by the James Webb Space Telescope (JWST) and future extremely large ground-based telescopes.

Luque stressed that small planets around larger stars are more difficult to get exact masses, but could soon be provided by another star. cutting-edge ultra-stable spectrographs.

New planet discoveries around M dwarf stars by NASA’s Transiting Exoplanet Survey Satellite (TESS) mission and mass determinations made by the CARMENES spectrometer installed 3.5 m from Calar Alto in Almería were the basis for this study. Southern Spain).