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Posted on 30 Apr 2019
Beautiful blue planets with infinite oceans can be in orbit around the trillion stars of the Milky Way. In 2016, for example, Kepler astronomers discovered planets that looked like nothing in our solar system – a global "water world" system orbiting the Kepler-62 star. This system of five planets has two worlds in the habitable zone – their surfaces are completely covered by an endless global ocean, without land or mountains in sight.
In our own solar system, the moon of Jupiter. Europa, under its icy surface, is home to a huge salty ocean that, according to scientists, reaches 100 km – a depth 10 times greater than that of the Marianas Pit.
According to Caltech's Mike Brown, the bedrock of the vast ocean of Europa almost looks like a miniature Earth, with plate tectonics, continents, deep trenches and active dispersal centers. "Think about the mid-ocean ridges on Earth," writes Brown on his blog, "with their black smokers spewing boiling, nutrient-rich water in a seabed that combines with the life that survives with these chemicals." It does not take much imagination to imagine the same type of rich chemical soup in the Europa Ocean leading to the evolution of a kind of life, taking advantage of the internal energy generated inside the heart of Europa. If you're looking for whales in Europe – what many of my friends and I often say jokingly is the world you want to look for. "
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The new research published today in the Proceedings of the National Academy of Sciences (PNAS) reinforces the chances that aquatic worlds are a common feature of the Milky Way. With the help of computer simulations, astronomer Li Zeng of Harvard University and his colleagues presented data showing that planets smaller than Neptune, that is, to say the planets whose radius is about two to four times that of the Earth, are probably aquatic worlds and not gaseous dwarfs. by thick atmospheres as traditionally believed.
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According to Zeng, some of these sub-Neptunian planets have oceans deep enough to exert pressures equivalent to one million times the atmospheric pressure at the surface. Under these conditions, the fluid water is compressed into ice phases under high pressure, such as Ice Seven or superionic ice. "These high-pressure ice sheets are essentially like silicate rocks in the deep mantle of the Earth, they are hot and hard," he said. "These are totally different worlds from our own Earth."
In contrast, the Earth has an obvious surface, with water compositions between 25 and 50% of the total mass of the planet, these objects would be completely waterlogged. They "may or may not have a well-defined surface," said Li, and they "could be fluid all the way through – up to the greatest depth".
Could these oceanic worlds support life? Maybe even a smart life? "There may be life there," says Lisa Kaltenegger, director of the Carl Sagan Institute in Cornell. "But could it be based on technology like ours? Life on these worlds would be under water without easy access to metals, electricity or fire for metallurgy. Maybe the inventiveness of life to switch to technology will surprise us. "
"The aquatic worlds of the Milky Way" – A great promise in the search for life
Could extraterrestrial worlds at some point change the life we know on Earth? "A purely oceanic world (without land at the surface)," wrote in an email to dailygalaxy.com Avi Loeb, chairman of the Harvard Astronomy Department, "will probably not develop the diversity of life as we know it because she will be exhausted. nutrients essential for life, such as phosphorus and molybdenum. "
"We generally think that liquid water on a planet is a way to start life, because life, as we know it on Earth, is composed mainly of water and requires its life," says astrophysicist Natalie Hinkel, Senior Researcher at Southwest Research. San Antonio Institute and co-investigator of the NExSS (Nexus for Exoplanet System Science) Research Network at the University of Arizona. "However, a planet that is an aquatic world, or one that does not have a surface above water, does not have the important geochemical or elementary cycles that are absolutely necessary for life. . "
"I think it could be dangerous to think of everything in an ecological state of mind," says Ramses Ramirez at the Tokyo Institute of Technology. "You might miss other possibilities."
New research suggests that about 35% of all known exoplanets that are larger than Earth should be water rich. The recently launched TESS mission will find much more, thanks to spectroscopic ground tracking. We hope that the next-generation James Webb Space Telescope will characterize their atmospheres with important implications for the search for life in the Milky Way.
"It was a huge surprise to realize that there had to be so many aquatic worlds," said Zeng.
The Earth's oceans themselves have become the vector of evolution, says Peter Godfrey-Smith in Other Minds. Godfrey-Smith writes that the terrestrial cephalopods of the ocean – octopus, squid and nautilus – are "an island of mental complexity in the sea of invertebrate animals," he has developed on a different path, "Independent experience in the evolution of big brains and complex behavior. "
"If we can come into contact with cephalopods as sentient beings, it 's not because of a common history, nor because of the kinship, but because the l? evolution has built minds twice, "says Godfrey-Smith. "It's probably the closest we will come to meet a smart alien."
The Daily Galaxy via Caltech, Arizona State University, Goldschmidt Conference, The Atlantic and Scientific American
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