Earthy exoplanets. Credit: NASA.
Today we know that the universe around us, at least in the Milky Way, is full of planets. And in many cases these are terrestrial exoplanets, more or less comparable with the earth. When it comes to planets that are two to four times larger than the earth, they are probably made up of water. This is the conclusion of recent research that his authors presented at the annual Goldschmidt conference of the American Geochemical Society in Boston.
Li Zeng. Credit: Harvard University.
When astronomers confirmed at the beginning of the nineties that there really were planets with strange stars, they became immediately interested in what these planets were composed of. The primary goal of such efforts was, of course, to find out whether the exoplanets were suitable for the existence of an earthly type of life. For a long time we did not have enough powerful devices for similar answers. In the era of the Kepler telescope exoplanet and Gaia Gaia Observatory it is different.
Sara Seager. Credit: MIT.
Li Zeng of Harvard and his colleagues analyzed data from Kepler and Gaia and concluded that many of the well-known exoplanets could contain up to 50 percent of the water. This is an enormous amount against the earth, which despite the seductive blue color contains only 2 hundred percent of the mass in the form of water. It was a big surprise for Zeng & # 39; s team. If they are right, we live in a galaxy of water worlds.
Researchers have collected data on the mass of the exoplanets and linked them to the data on their dimensions recently acquired by the Gaia Observatory. In this way they came to the models of the internal structure of the studied exoplanets. Their models show that planets with a diameter of 1.5 times our earth are usually stone planets, usually the masses of five earths. And planets with a diameter of 2.5 times the earth, whose weight is about 10, are water worlds according to their models.
European Gaia observatory. Credit: ESA / ATG medialab; background: ESO / S. Brunier.
But according to Zengo, it is not about such water worlds as we dreamed in science fiction stories. It is rather a steam world with a surface temperature between 200 and 500 degrees Celsius. The surface of such planets is thus covered with hot steam including a layer of liquid water. If we go to the depths of such a planet, we will encounter remarkable ice created by extreme pressure, and ultimately the stone core of the planet.
The results of the Zeng team suggest that about 35 percent of all known exoplanets, which are larger than Earth (almost all), are water worlds. During the development of planetary systems such planets emerge in the same way as the gigantic gas giants known from the solar system. The recently launched TESS (Transiting Exoplanet Survey Satellite) mission needs to find many more such worlds so that we can thoroughly explore them. When the James Webba telescope ever enters the universe, they will also look at the teeth.
The scientific director of the TESS mission is enthusiastic about the idea that the exoplanets, slightly larger than our earth, can be water worlds with a huge amount of water. He fervently hopes that observation of such planets in the near future will reveal whether they are covered with a thick layer of water vapor, which would reveal itself as water worlds. Or we learn that the water worlds are not. Planetary scientists will not get bored right now.
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Phys.org August 17, 2018, Goldschmidt conference.