Earth Twins Are Probably Not Blue


Seeking dry “pale yellow dots” and frivers might have a better chance of success than a pale blue in identifying Earth-like worlds around other stars.

The close balance between land and water that has helped life flourish on Earth could be highly unusual, according to a Swiss-German study presented at the Europlanet 2022 Scientific Congress in Granada.

Tilman Spohn and Dennis Höning studied how the evolution and cycles of continents and water might shape the development of terrestrial exoplanets. Their model results suggest that the planets have about an 80% chance of being mostly covered by land, with a 20% chance of being mostly ocean worlds. Only 1% of the results had a distribution of land and water similar to that of the Earth.

“We Earthlings enjoy the balance between land areas and oceans on our home planet. It’s tempting to assume that a second Earth would be like ours, but the results of our model suggest that this is not likely to be the case.”said Professor Spohn, Executive Director of the International Space Science Institute in Bern, Switzerland.

The team’s numerical models suggest that the average surface temperatures would not be much different, perhaps with a variation of 5° Celsius, but that the land-ocean distribution would affect the climates of the planets. An ocean world, with less than 10% land, would likely be humid and warm, with a climate similar to that of Earth in the tropical and subtropical times that followed the asteroid impact that caused the extinction of the dinosaurs.

The continental worlds, with less than 30% oceans, would have colder, drier and harsher climates. Cold deserts could occupy the inner parts of land masses and would generally resemble our Earth at some point during the last Ice Age, when extensive glaciers and ice sheets developed.

On Earth, the growth of the continents by volcanic activity and their erosion by weathering is roughly balanced. Photosynthesis-based life thrives on land, where it has direct access to solar energy. The oceans they provide a huge reservoir of water that increases rainfall and prevents the current climate from becoming too dry.

“In the engine of Earth’s plate tectonics, internal heat drives geological activity, such as earthquakes, volcanoes, and mountain building, and results in the growth of continents. The erosion of the land 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 today’s Earth may be an exceptional planet, and that the Earth’s mass balance may be unstable for billions of years. While all the modeled planets could be considered habitable, their fauna and flora can be very different.said Professor Spohn.

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