Scientists recently deduced based on a new study that exoplanets planets with land-to-ocean ratios like Earth may be rare in the entire universe.
In the study, it was found that exoplanets whose 30% of their surface is made up of exposed continental land surface make up about 1% of the entire rocky planets found in numerous star systems despite sitting at their local planet’s habitable zones.
On the other hand, about 80% of the potentially habitable planets are completely dominated by land while only 20% are purely oceans without any dry land.
The researchers arrived at this conclusion by modeling the relation between water in a planet’s mantle and a planet’s recycling of continental land via plate tectonics.
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The researchers came to this conclusion by modeling the relationship between water in a planet’s mantle and a planet’s recycling of continental land via plate tectonics.
“We Earthlings enjoy the balance between land areas and oceans on our home planet,” Tilman Spohn, executive director of the International Space Science Institute in Switzerland and a member of the research team, said in a statement.
“It is tempting to assume that a second Earth would be just like ours, but our modeling results suggest that this is not likely to be the case.”
Based on the results of the study, Earth’s land-to-sea ratio is finely balanced even though that may not be the case for most planets which usually fall on either extreme side.
Spohn and his collaborator, Dennis Höning, a postdoctoral researcher at the Potsdam Institute for Climate Impact Research in Germany, concluded that the most likely time for this tipping point to occur is when a planet’s interior has cooled close to the temperature of Earth’s mantle, which is 2,570 degrees Fahrenheit (1,410 degrees Celsius) near the crust and as hot as 6,700 F (3,700 C) at greater depths.
The research also found that the better subduction zones at the boundaries between tectonic plates can cycle water over land at the mantle temperature will dictate if a planet will be dominated either by land or water.
Our planet Earth reached these conditions 2.5 billion years ago, right at the end of the Archean and the planet has been able to find a perfect balance between land and water.
However, things weren’t so great for the planet billions of years back despite researchers not entirely catching sight of this dye to the rates of little changes.
Other planets could have reached this tipping point much sooner.
“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,” Spohn said.
On the other hand, “The land’s erosion 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 present-day Earth may be an exceptional planet.”
Another thing both Spohn and Höning also considered is the effects of carbon dioxide which contributes to the carbon-silicate cycle that acts as a planet’s long-term thermostat that helps to control climate over millions of years.
They found that, while both land- and ocean-dominated planets could still be habitable, with similar temperatures if all else were equal, their life forms and climates might not be quite unlike Earth’s.
“Their fauna and flora may be quite different,” Spohn said.
In their models, it was shown that planets dominated by oceans with less than 10% land are likely going to be warmer with moist atmospheres and tropical climates while those that are land-dominated with less than 30% of their surfaces being covered by ocean would be much colder, harsher, and drier.
On these land-dominated planets, cold deserts would stretch across the landmasses, and vast glaciers and ice sheets would be common.
One thing though is the fact that Spohn and Höning’s results are quite different from the results of other research teams.
A good example would be a study made by Evelyn MacDonald of the University of Toronto who found that for tidally-locked planets, the more land there is, the greater the average surface temperatures in general.
While the other one is led by Yukata Abe of the University of Tokyo as far back as 2011 which found that land planets can remain habitable across much wider distances from their star than water worlds can and that they don’t freeze over as fast because there is less water for ice and snow.
However, Abe’s study, along with others, agrees with Spohn and Höning’s conclusion that land-dominated planets would be far more common than Earth-like or water-rich planets.
Findings were shown at the European Science Congress which took place in Granada, Spain from Sept. 18th to 23rd.