'Pale blue dot' planets like Earth may make up only 1% of potentially habitable worlds

Earth-like worlds with similar land to ocean ratios are very rare.

According to a new study, Earth-like planets with about 30% of their surface covered by exposed continental land may make up only 1% of rocky worlds in stars' habitable zones. The study found that 80% of potentially habitable worlds are dominated by land.

Water in a planet's mantle is related to a planet's recycling of continental land via plate tectonics, according to the researchers.

The Earth's 'Goldilocks' climate has been maintained by plate tectonics.

Tilman Spohn is the executive director of the International Space Science Institute in Switzerland and a member of the research team. Our results suggest that a second Earth is not likely to be the same as ours.

The results show that the Earth's ratio of land to sea is balanced and that it can easily tip over for most planets. The most probable time for this tipping point to occur is when a planet's interior has cooled close to the temperature of Earth's mantle. Whether a planet will be dominated by land or ocean depends on how well subduction zones can cycle water over land.

At the end of the Archean about 2.5 billion years ago, our planet found a balance that is still present today. Earth's fine balance is not stable because the rates of change are small. The tipping point for other planets could have been much earlier.

Spohn said that internal heat drives geologic activity 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 inside. Our models show how these cycles interact with each other.

The outgassing of carbon dioxide contributes to the carbon-silicate cycle that acts as a planet's long-term thermostat controlling the climate over millions of years. The life-forms and climates of both land and ocean-dominated planets might not be the same as on Earth.

Spohn said that the fauna and flora might be different.

The models indicated that ocean-dominated planets with less than 10% land would be warm, with moist atmospheres and tropical climates, whereas land-dominated planets with less than 30% of their surface covered in ocean would be cold, dry and harsher. Glaciers and ice sheets are common on land-dominated planets.

The results of Spohn and Hning differ from those of other teams. According to Space.com, a study by Evelyn MacDonald of the University of Toronto found that the more land there is, the hotter the surface temperatures. The most famous study of land planets was done by Yutaka Abe of the University of Tokyo in 2011. According to Abe's study, land-dominated planets would be more common than water-rich ones.

Astronomers should be looking for "pale yellow dots" instead of looking for " pale blue dots"

The results were presented at the European Science Congress and the findings are described in the abstract.

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