Exoplanets that resemble Earth in their seas, continents, and coastlines might be far more numerous than previously imagined.
But about 1% of the rocky planets in the habitable zones of stars, the regions where liquid water may exist on a planet's surface, may be Earth-like planets with around 30% of their surface covered in exposed continental land.
Instead, the study discovered that around 80 percent of possibly livable worlds are entirely dominated by land. In comparison, about 20 percent are entirely oceanic worlds.
Exoplanets May Not Be The Typical Earth-Like Pale Blue Dot After All
Researchers in Europe claim that pale blue spots similar to our globe are probably not very frequent. Alternatively, many livable worlds may be drier and colder than our own. These locations may also appear like pale yellow spots since they may have less water.
To better understand how the formation of habitable worlds could be influenced by the evolution of continents and planetary water cycles, planetary scientists Tilman Spohn and Dennis Höning constructed hypothetical exoplanets. They concluded that planets had an 80% chance of having primarily land cover. In other words, the terrain would be principally continental. Another 20 percent of potentially viable planets would probably be primarily marine. The distribution of land and water on Earth would be a minuscule fraction (less than one percent).
"We Earthlings enjoy the balance between land areas and oceans on our home planet," said Spohn, executive director of the International Space Science Institute in Bern, Switzerland (via Universe Today).
"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," added Spohn.
A Balance Between Land-To-Sea Ratio on Earth
The findings suggest that Earth's land-to-sea ratio (1:3) is delicately balanced and that this ratio may easily tip over to being predominantly land or mostly sea for most planets. The most likely time for this tipping point to occur, according to Spohn and Höning, is when a planet's interior has cooled down to a temperature similar to that of the Earth's mantle.
For context, the planet's mantle is 2,570 degrees Fahrenheit (1,410 degrees Celsius) just next to the crust and as hot as 6,700 F (3,700 C) at greater depths. A planet's dominance by land or ocean depends on how successfully subduction zones at the tectonic plate boundaries can cycle water over land at this mantle temperature.
At the end of the Archean, when Earth achieved these circumstances, it discovered the delicate equilibrium in which humans currently reside. Even Earth's delicate equilibrium is unstable over billions of years, though we are unaware of it since the rates of change are so slow, according to Spohn. This trough may have been reached considerably sooner by other planets.
Researchers presented their study, "Land/Ocean Surface Diversity on Earth-like (Exo)planets: Implications for Habitability," last Sept. 18 to 23 in Spain.
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