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Most Habitable Planets May Lack dry Land, Say Scientists

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Most habitable planets may lack dry land and would be dominated by oceans spanning over 90 per cent of their surface area, scientists say. Researchers at the University of Barcelona in Spain have constructed a statistical model – based on Bayesian probability – to predict the division between land and water on habitable exoplanets.

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For a planetary surface to boast extensive areas of both land and water, a delicate balance must be struck between the volume of water it retains over time, and how much space it has to store it in its oceanic basins.Both of these quantities may vary substantially across the full spectrum of water-bearing worlds, and why the Earth’s values are so well balanced is an unresolved and long-standing conundrum.

The model predicts that most habitable planets are dominated by oceans spanning over 90 per cent of their surface area.This conclusion is reached because the Earth itself is very close to being a so-called ‘waterworld’ – a world where all land is immersed under a single ocean. “A scenario in which the Earth holds less water than most other habitable planets would be consistent with results from simulations, and could help explain why some planets have been found to be a bit less dense than we expected,” said Fergus Simpson, from University of Barcelona.

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Simpson found that the Earth’s finely balanced oceans may be a consequence of the anthropic principle which accounts for how our observations of the universe are influenced by the requirement for the formation of sentient life. “Based on the Earth’s ocean coverage of 71 per cent, we find substantial evidence supporting the hypothesis that anthropic selection effects are at work,” said Simpson.

To test the statistical model Simpson has taken feedback mechanisms into account, such as the deep water cycle, and erosion and deposition processes.He also proposed a statistical approximation to determine the diminishing habitable land area for planets with smaller oceans, as they become increasingly dominated by deserts.

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Simpson suggests that a selection effect involving the balance between land and water caused life to evolve on this planet and not on one of the billions of other habitable worlds. “Our understanding of the development of life may be far from complete, but it is not so dire that we must adhere to the conventional approximation that all habitable planets have an equal chance of hosting intelligent life,” Simpson said. The study was published in the journal Monthly Notices of the Royal Astronomical Society.

Astronomers have for the first time detected an atmosphere around an Earth-like planet just 39 light years away, a significant step towards the detection of life beyond our solar system. Scientists, including those from Max Planck Institute for Astronomy in Germany, studied the planet known as GJ 1132b, which is 1.4-times the size of our planet.

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They imaged the planet’s host star, GJ 1132, and measured the slight decrease in brightness as the planet and its atmosphere absorbed some of the starlight while passing directly in front of their host star. The detection of an atmosphere around the super-Earth GJ 1132b marks the first time an atmosphere has been detected around a planet with a mass and radius close to Earth’s mass and radius (1.6 Earth masses, 1.4 Earth radii), researchers said.

The new observations showed the planet to be larger at one of the infrared wavelengths than at the others.This suggests the presence of an atmosphere that is opaque to this specific infrared light (making the planet appear larger) but transparent at all the others.Different possible versions of the atmosphere were then simulated by team members at the University of Cambridge and the Max Planck Institute for Astronomy.

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According to those models, an atmosphere rich in water and methane would explain the observations very well.Observations to date do not provide sufficient data to decide how similar or dissimilar GJ 1132b is to Earth. Possibilities include a “water world” with an atmosphere of hot steam, researchers said. “GJ 1132b provides a hopeful counterexample of an atmosphere that has endured for billion of years.

Given the great number of M dwarf stars, such atmospheres could mean that the preconditions for life are quite common in the universe,” they said. The research was published in the Astronomical Journal.

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