Search for new Earths should look for ‘pale yellow dots,’ not blue: Research

New research suggests that the search for Earth-like worlds should look for dry, cold “pale yellow dots” instead of “pale blue dots” like Earth. According to the study presented at the Europlanet Science Congress this year in Grenada, the near balance of land and water that helped life flourish on Earth could be very uncommon.
Researchers Tilman Spohn and Dennis Honing modelled how the development of terrestrial exoplanets can be shaped the evolution and cycles of continents and water. Their research suggests there is an 80 per cent probability of terrestrial exoplanets being mostly covered land. Also, there is approximately 19 per cent probability of such planets being oceanic worlds. They found that there is only about a one per cent chance of such planets having an Earth-like balance of ocean and land.
“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 Spohn in a press statement. Spohn is the Executive Director of the International Space Science Institute in Bern, Switzerland.

The numerical models suggest the average surface temperatures on these planets would not be too different, maybe with a variation of around 5 degrees Celsius. On the other hand, the ratio of land and ocean would have a big effect on the planets’ climate. An oceanic world with less than 10 per cent land would have a mostly warm and mo climate. Conversely, continental worlds with less than 30 per cent oceans would have colder and drier climates, with cold deserts occupying the inner parts of the landmasses.
“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,” explained Spohn
On our planet, the growth of continents is roughly balanced with their erosion. Lifeforms that depend on photosynthesis can thrive on the land where they get direct access to solar energy while the ocean provides a huge reservoir of water that prevents the climate from getting too dry.
“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,” added Spohn.