Scientists: habitable exoplanets must be very different from Earth

When searching for Earth-like planets in other star systems, instead of looking for a "pale blue dot", it is better to look for dry, cold and "pale yellow" worlds. This is stated in the new scientific workLand/Ocean Surface Diversity on Earth-like (Exo) planets: Implications for Habitabilitypresented at the Europlanetary Science Congress 2022 in Granada. According to its authors, the close balance between land and water, which helped the development of life on Earth, may be much rarer than previously thought.

A team of scientists from Germany and Switzerland, led by Tilman Spon and Dennis Hoening, studied how the evolution and cycles of continents and water can influence the development of terrestrial exoplanets. The results of their simulation showed:

• there is about an 80 percent chance that habitable planets are mostly land-based;
• only 20 percent of the time can worlds be mostly covered in water;
• and only 1 percent of the results obtained had a terrestrial, balanced, distribution of land and water.

The team's other models suggest that average surface temperatures won't vary much, perhaps as little as 5°C. However, the distribution of land and water will necessarily affect the climate. Thus, an oceanic world with less than 10 percent land would probably be humid and warm. The weather there should be similar to Earth's during the era of the tropics and subtropics, following the fall of the asteroid that caused dinosaur extinction.

Continental worlds where oceans cover less than 30 percent of the surface will experience colder, drier, and harsher climates. Cool deserts could occupy the interior of land masses, and in general they would resemble ours. Earth somewhere during the last ice age, when extensive glaciers and ice shields.

On Earth, the growth of continents due to volcanic activity and their erosion due to weathering are approximately balanced. Life based on photosynthesis thrives on land, where it has direct access to solar energy. The oceans, on the other hand, are a huge volume of water that increases rainfall and prevents the current climate from becoming too dry.