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Home / Science / Water worlds could have incredibly deep oceans, propose new models

Water worlds could have incredibly deep oceans, propose new models

Artistic representation of a water world.
Image: NASA / JPL-Caltech

Scientists have good reason to believe that so-called water worlds – exoplanets covered with surfaces entirely from a single giant ocean – are common in the galaxy. However, new computer simulations suggest that not only water worlds are prevalent, but also that they are bursting with water – and at astounding scales. Imagine oceans that are hundreds and even thousands of miles deep.

New research published today in Proceedings of the National Academy of Sciences confirms the growing case that water worlds are a common feature of the Milky Way. Using computer simulations, Harvard University astronomer Li Zeng and his colleagues presented new data showing that sub-Neptune-sized planets, d. H. Planets with radii approximately two to four times the size of the Earth, probably water worlds and no gas dwarf skins are surrounded by thick atmospheres, as is conventionally assumed.

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To be clear, water worlds, also known as ocean worlds, are still hypothetical. Unless, of course, we include Jupiter's moon Europa and Saturn's moon Enceladus, which are believed to have enveloped global oceans in an icy crust. However, planetary design models suggest that water worlds are real and probably very common. For example, research from 2017 has suggested that the most livable earth-like planets could actually be water worlds.

For the new study, Li & # 39; s team attempted to further refine our planet formation models. Observations from Kepler and other observatories have enabled astronomers to identify thousands of exoplanets, many of which are in close proximity to their guest stars (close-ups make us even closer than Mercury to our Sun). These data indicate two dominant species of exoplanets one to four times the size of Earth: dense rocky worlds (called super-earths) or medium-sized planets with relatively low densities. This last category is of interest to the new study because scientists are not sure if these exoplanets have a rocky core surrounded by a dense, hydrogen-rich atmosphere (eg a gas dwarf) or if they contain a significant amount of water Ice or liquid or a combination of the two (ie water worlds).

Conventional thinking suggests that they are gas dwarfs because water worlds can only form beyond the "snow line" of a planetary system (the distance from the host star, where it is cold enough for volatile compounds to turn into solid ice grains form). The new computer models, however, suggested that these sub-Neptunes should have very modest atmospheres in size – certainly nothing that does not suit a gas dwarf. In the meantime, simulations of the growth and evolution of the planet revealed many medium-sized planets as water worlds.

This finding then supports another emerging theory, that of planetary migration. Because water worlds can form only in the outer region of a star system and because so many sub-Neptunes are in close proximity to their host stars, this research provides theoretical evidence that planets – including water worlds – slowly drift inward over time.

"It's incredible. Bottomless Very Deep. "

Sub-Neptunian water worlds are likely to be exceptionally humid, according to new research. At least 25 percent of the total mass of these planets would consist of water-dominated ice and liquids. Some of these planets could even be 50 percent water. These water worlds are not just planets without terrestrial surface features – they are essentially water-filled spheres with pieces of rock and metal thrown for good reason. In comparison, the earth is mostly rocky with a water content of about 0.025 percent of its total mass and an atmospheric water content, which accounts for only one millionth of its total mass.

Sub-Neptunian water worlds are "not just submerged," Li said in an email to Gizmodo. They have sea depths that exceed "hundreds or thousands of kilometers of depth, rather than a few miles deep, like the oceans of the earth." and he added a few suitable descriptors: "Incredible. Bottomless Very Deep. "

Or at least computer simulations have suggested this. The models used in the study simulated planetary formation processes, influenced by the abundance of fog gases, water-rich ice, and various rocky materials consisting mainly of iron and nickel, and influenced by complex chemical processes that are affected by temperature, cooling rates, and evaporation , Condensation, density and distance to the host star, among many other factors.

Looking at the simulations, Li was impressed by the amount of water in the galaxy and its importance during the planet formation phase.

"Statistically, these water worlds may be richer than Earth-like rocky planets," Li told Gizmodo. "Perhaps every typical sun-like star has one or more of these water worlds [and maybe]. Our solar system is less typical. In general, this type of planetary system architecture with nearby rocky super-earths and water-rich sub-Neptunes in the Milky Way may be more common than our solar system. "Some of these planets."

He said that the oceans are deep enough to withstand a pressure of one million times our atmospheric surface pressure, under which liquid water is compressed in high-pressure phases of ice, such as Ice Seven Seven (19459041 ) or superionic ice cream.

"These high pressure ice are essentially silicate rocks in the Earth's deep mantle – they are hot and hard," he said. "These are completely different worlds from our own."

Our Planet has an obvious surface, but sub-Neptunian water worlds are not that much – with water compositions that make up between 25 and 50 percent of the planet's total mass, these objects would be completely water-protected. "They may or may not have a well-defined surface," Li said. and they could be "all the way down – all the way down to the deep."

Sean Raymo nd, an astronomer from the University of London Bordeaux, who was not involved in the new study, said the newspaper was fine.

"Its conclusions are statistical, meaning that the authors do not point to certain planets and call them waterworlds, but focus on the population as a whole," Raymond Gizmodo said in an email. "Still, it's a cool paper and a provocative result."

Raymond was particularly surprised at how the study further substantiated the hypothesis of planetary migration.

"A water world that is close to its star must have moved much farther and then moved closer as its orbit shrank. The composition of the planet was fixed as it lay on a colder orbit, "he said. "The process of orbital shrinkage is called" migration "and is determined by the gravity of the gas disk that formed the planets. When water worlds are common, this is a very strong validation that migration is actually taking place and is a crucial process for planet formation – both in other stars and in our own solar system.

Raymond also found it interesting that the water content of 25 percent is about the same as for outer Solar System objects like Pluto and Comet 67P. "This fits in with the migration history that these waterworlds may have been born far from their stars before migrating inward," he said. "I like such simulations," said Anders Sandberg, a research associate at the University of the Future University of the University of Humanity Institute, also not involved in the new study, wrote in an email to Gizmodo. "The really cool thing is that this paper is, in a sense, a bet on what we'll discover in the next few years: the actual data gathers at a wonderful rate that allows us to verify that the prediction is correct."

A nice aspect of this work is that the results tell us what to look for when we get access to the next generation of space telescopes, including the James Webb telescope and the ESA Space Telescope Ariel. Sandberg also said that the new insight has an impact on the search for someone else's life.

"Water worlds may not be perfect for life, as the heavier elements may be buried under hundreds of miles of high-pressure ice, but probably far better than gas dwarves," he said.

Whether it's a water-soaked planet contributing to a smart, space-borne species or not is a very different question and certainly a question that, given the apparent abundance of these considerations, is of concern to planets in the galaxy.

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