| Sep 20, 2022 |
Earth-like exoplanets unlikely to be another 'pale blue dot'
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(Nanowerk News) Tilman Spohn and Dennis Höning studied how the evolution and cycles of continents and water could shape the development of terrestrial exoplanets. Results from their models suggest that planets have approximately an 80 percent probability of being mostly covered by land, with 20 percent likely to be mainly oceanic worlds. Barely one percent of the outcomes had an Earth-like distribution of land and water (Europlanet Science Congress 2022, "Land/Ocean Surface Diversity on Earth-like (Exo)planets: Implications for Habitability").
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“We Earthlings enjoy the balance between land areas and oceans on our home planet. It is tempting to assume that a second Earth would be just like ours, but our modelling results suggest that this is not likely to be the case,” said Prof Spohn, Executive Director of the International Space Science Institute in Bern, Switzerland.
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| Modelling shows that the probabilities of three very-different looking types of terrestrial planets (covered with land, ocean or an equal mix of both) vary widely, while highly impacting their climate and thus their habitability. (Image: Europlanet 2022 RI/T. Roger)
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The team’s numerical models suggest that the average surface temperatures would not be too different, with perhaps a 5 °C variation, but that the land-to-ocean distribution would affect the planets’ climates. An ocean world, with less than 10 percent land, would likely be moist and warm, with a climate similar to the Earth in the tropic and subtropic epoch that followed the asteroid impact that caused the extinction of the dinosaurs.
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The continental worlds, with less than 30 percent oceans, would feature colder, drier and harsher climates. Cool deserts might occupy in the inner parts of landmasses, and overall they would resemble our Earth sometime during the last Ice Age, when extensive glaciers and ice-sheets developed.
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On Earth, the growth of continents by volcanic activity and their erosion by weathering is approximately balanced. Life based on photosynthesis thrives on land, where it has direct access to solar energy. The oceans provide a huge reservoir of water that enhances rainfall and prevent the present climate from becoming too dry.
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“In the engine of Earth’s plate tectonics, internal heat drives geologic activity, such as earthquakes, volcanoes and mountain building, and results in the growth of continents. The land’s erosion is part of a series of cycles that exchange water between the atmosphere and the interior. Our numerical models of how these cycles interact show that present-day Earth may be an exceptional planet, and that the equilibrium of landmass may be unstable over billions of years. While all the planets modelled could be considered habitable, their fauna and flora may be quite different,” said Prof. Spohn.
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