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Astronomy: Discover an exoplanet surrounded by an ocean

Astronomy: Discover an exoplanet surrounded by an ocean

A so-called “red dwarf,” Kepler-138 is much smaller and cooler than our sun. Co-authors said that the star, which is located outside our solar system, has several planets orbiting it Luca Fossati from the Graz Institute for Space Research (International Monetary Fund) to APA.

It was discovered in 2014 by the Hubble and Spitzer space telescopes. In this planetary system, something surprising has now been discovered about the planet Kepler-138d, which is about 1.5 times the size of Earth. were the visions In the journal “Nature Astronomy” released.

The rocky planets and minor Neptune

To date, about 5,000 exoplanets – celestial bodies outside the solar system – are known. So far exoplanets with a radius of less than 1.7 have been assigned to the classes of rocky planets or small Neptunes: rocky planets orbit their star in very narrow orbits, which means they lose their atmospheres over time due to the influence of the stars. radiation.

Benoit Goujon, University of Montreal

The internal structure of the Earth compared to the planet outside the solar system Kepler 138 d

On the other hand, small, gaseous Neptunes accumulated so much hydrogen gas during their formation that they – like the large gaseous planets in the outer solar system – no longer lose it to space. According to the Graz Space Institute, the same applies to the so-called Hycean planets, which are hypothetical celestial bodies surrounded by an ocean of hot water and an atmosphere very rich in hydrogen.

Conditions are specific to Kepler-138d: According to simulations by the IWF scientist and co-author Daria Kopechenka It would be almost impossible for the planet to have a hydrogen shell: it would have been lost to space in ten million years. Since it is estimated to be between 1 and 2.7 billion years old, it cannot be a minor Neptune planet or a hickey planet.

Kepler-138d first “oceaning planet”

Scientists have observed planetary transits of Kepler-138d with the help of space telescopes. The planet moves in front of its parent star in a kind of ministerial eclipse and its light weakens slightly. From the strength of this weakness, the size and gravity of the planet can be calculated and the presence of individual chemical elements in the atmosphere can be demonstrated. The data were supplemented with radial velocity measurements. At the moment, none of them have provided any evidence of the existence of liquid water.

However, by comparing the exoplanet’s size and mass with simulation models, the team of astronomers concluded that much of its volume must be composed of matter lighter than rock but heavier than hydrogen or helium: the most common of these is water. .

“Dual modeling of the planet’s interior and atmospheric structure, consistent with extensive observations, supports the hypothesis that the rocky, Earth-like core of Kepler-138d is likely surrounded by a 2,000-kilometer-deep water ocean and a fluctuating atmosphere,” Fossati said. So the ocean on Kepler-138d would be 500 times deeper than Earth’s average. The so-called “ocean planets” were hypothesized about 20 years ago. In the first relevant publication he was the head of the IMF group Helmut Lammer Just like in the current study. It now appears that Kepler-138d is the first exoplanet to actually conform to the nomenclature.

Life is unlikely

In 2013, Lammer identified planetary habitats with large layers of water over a rocky core: the possible living conditions in such potential habitats (habitat class V) depend on extreme conditions in the deep sea. “However, Kepler-138d is a subclass of such a habitat,” Lammer explained. Because a layer of water 2000 km thick is unusually heavy, which means that there is very high pressure in the lowest layer of water – where water and rock come into contact.

“Because of the huge amount of water, it is very likely that high-pressure ice, or even water, will form in another phase that occurs at high pressure, called a supercritical fluid. These extreme conditions prevent contact between the water on the surface and the minerals in the rocky body below.” This is from This would prevent the emergence of life as we know it, making it unlikely that life could ever exist on Kepler-138d.