Two planets composed mainly of water have been discovered. They are unlike anything in the solar system.

Scientists from the University of Montreal took a closer look at the planetary system of the star Kepler-138, which is 218 light-years from Earth. The researchers used observations provided by Cosmic telescope Hubble and the now defunct Spitzer Space Telescope. Your search results wash Described in the journal Nature Astronomy.

Two water worlds apart from everything we know

The research shows that Kepler-138c and Kepler-138d, two — previously discovered by the Kepler space telescope — exoplanets are more than half made up of water. Although it has not been directly detected, data on the size, mass, and density of these objects suggest it.

Astronomers were able to determine that the two planets are similar twins, but they differ significantly from terrestrial planets (such as Earth). Kepler-138 c and Kepler-138 d have twice the mass of our planet, but twice the density. The researchers compared the data with the models and concluded that the planets cannot be either rocky or gaseous worlds.

Half, or just over half, of the building materials for both planets is something lighter than rock but heavier than hydrogen and helium (these two are the main constituents of gas giants). By far, the most likely candidate in this case is water.

Giant oceans and steam clouds

The researchers suggest that Kepler-138 c and Kepler-138 d probably cover a global water ocean, and that the planets are also surrounded by an atmosphere of water vapor. As he writes in his communication NASAbodies are “unparalleled in our solar system” and are the best candidates for representatives of ocean planets (or the so-called water worlds), the existence of which was predicted long ago.

Two planets that are mostly made of water have been discovered. They are not like anything in the solar system Photo: Benoit Gougeon (University of Montreal

However, there are several indications that the water on these planets is not the same as that found in Earth’s seas. Kepler-138 cid orbits its star at short distances, and the prevailing temperatures there are much higher than those on Earth and exceed the boiling point of water. Most of the water on exoplanets is probably working the border liquid and gaseous state or in the supercritical state (where the boundary between gas and liquid disappears). Only at the bottom can there be liquid water under enormous pressure.

As the researchers calculated, Kepler-138 d has a rocky metallic “core” that’s just under half the size of an exoplanet. And above it stretches a global water and gaseous ocean about two thousand meters deep. km (for comparison, the average depth of the oceans on Earth is “only” 4 km). Above that is a layer of gaseous atmosphere consisting mainly of water vapor.

The temperature in Kepler-138 d’s atmosphere is likely to be above the boiling point of water, and we would expect a thick, dense atmosphere of water vapor on the planet. Only under this gaseous atmosphere can there be high-pressure liquid water, and even water in another high-pressure phase, called the supercritical state.

– explains Caroline Piaulet of the University of Montreal, who led the research.

A brand new exoplanet has been found in the habitable zone

This is not the end of the discoveries made by the team of researchers from Montreal. So far, only three planets have been known to orbit the star Kepler-138. In addition to planets Kepler-138 c and d, there was also a known planet b, which – as it has now been confirmed – has the mass of Mars and is one of the smallest exoplanets known to us. However, all three objects are too close to their star for life to exist.

Now, however, scientists have found evidence of a fourth planet for this system – Kepler-138 e. And it is located farthest from the star – in the so-called habitable zone, where liquid water can be found and there are favorable conditions for the development of life. Unfortunately, this planet cannot be observed by the transit method, that is, while passing in front of the star (this is the most common method for detecting and studying exoplanets).

Scientists were only able to determine that Kepler-138 e is a small rocky planet that orbits its star every 38 days. More observations are needed to find out Title Anything extra.

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