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Earth-like habitable planets highly unlikely

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HQ Team

October 6, 2022: The likelihood of finding an Earth-like planet with the correct ratio of land to water mass and a flourishing environment is highly unlikely, according to a Swiss-German study presented at the Europlanet Science Congress 2022 in Granada. According to the study, Earth-like planets with about 30% land mass and the rest under water are less than 1%.

The study found that roughly 80% of potentially habitable worlds are completely dominated by land, and about 20% are purely ocean worlds.

The research, co-authored by the Swiss-German team of Tilman Spohn and Dennis Höning, used computer models of more than a thousand potential terrestrial planets charting the relationship between water in a planet’s mantle and a planet’s recycling of continental land via plate tectonics. The researchers found that the Earth’s land-to-water ratio of 1:3 is ideal and that for others, this ratio tips over to mostly land or mostly oceans.

“We Earthlings enjoy the balance between land areas and oceans on our home planet,” Tilman Spohn, said in a statement. “It is tempting to assume that a second Earth would be just like ours, but our modeling results suggest that this is not likely to be the case.” 

Earth reached the ideal conditions about 2.5 billion years ago, at the end of the Archean, and our planet found the delicate balance we live in today. However, after billions of years, now even Earth’s fine balance is unstable, although unnoticeable, Spohn said.

“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,” Spohn said. On the other hand, “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.”

Another factor that contributes to life on Earth, according to Spohn and Höning is carbon dioxide or the greenhouse gas that controls the climate over millions of years. They say that even though both land and ocean-dominated planets could be habitable, keeping all the other factors equal, still the life forms there would be dis-similar to our Earth.

“Their fauna and flora may be quite different,” Spohn said.

Their models indicate that ocean-dominated planets with less than 10% land would likely have tropical climates, whereas land-dominated worlds with less than 30% of their surfaces under oceans would be colder and drier. Here, the land mass would likely be vast deserts of glaciers and ice sheets.

This latest study differs from the most famous study of land planets, led by Yutaka Abe of the University of Tokyo in 2011, which said that land planets at a massive distance from their star can be habitable compared to the water-dominated ones. This is because there is less likelihood of them freezing over.

However, Abe’s research matches the latest study in finding that land-dominated planets would be far more common than Earth-like or water-rich planets. 

The findings can be read here.

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