When searching for Earth-like worlds around other stars, rather than searching for the “faint blue dot” described by Carl Sagan, new research suggests that searching for dry, cool “faint yellow dots” may have a better chance of success.
The close balance between land and water that helped life thrive on Earth may be very unusual, according to a Swiss-German study presented at the 2022 Europlanet Science Conference in Granada.
Tilman Spoon and Dennis Hoeing studied how the evolution and cycles of continents and waters could shape the evolution of terrestrial exoplanets. Results from their models suggest that the probability of the planets covering roughly 80 percent of the Earth, with 20 percent of them being primarily oceanic worlds. Barely one percent of the results had a land-like distribution of land and water.
“We earthlings enjoy a balance between our planet’s land and ocean regions. It is tempting to assume that a second Earth will be just like our own, but our modeling results suggest that it is unlikely,” said Professor Spoon, executive director of the International Institute for Astronomy in Bern, Switzerland. That this be the case.”
The team’s numerical models indicate that average surface temperatures won’t be very different, perhaps with a difference of 5 degrees Celsius, but the distribution from land to ocean will influence planetary climates. The ocean world, with less than 10 percent of Earth, is likely humid and warm, with a climate similar to Earth in the tropical and subtropical epochs that followed the asteroid impact that caused the extinction of the dinosaurs.
Continental worlds, containing less than 30 percent of the oceans, will have cooler, drier, and harsher climates. Cold deserts may occupy the interior of land masses, and in general will resemble our Earth sometime during the last Ice Age, when glaciers and ice sheets developed.
picture It shows Earth from a distance of 6 billion km, captured by NASA’s Voyager 1 spacecraft in 1990. It has become code-named as the “faint blue dot.” The image was recently processed and released by NASA in 2020. Credit: NASA / JPL-Caltech
On Earth, the growth of continents through volcanic activity and erosion by weather factors is roughly balanced. Photosynthesis-based life thrives on Earth, where it has direct access to solar energy. The oceans provide a huge reservoir of water that enhances precipitation and prevents the current climate from becoming too dry.
“In the engine of Earth’s tectonic plates, internal heat drives geological activity, such as earthquakes, volcanoes, and mountain formation, and leads to the growth of continents. Earth erosion is part of a series of cycles that exchange water between the atmosphere and the interior. Our digital models of how these cycles interact show that the present-day Earth It may be an exceptional planet, and the Earth’s mass balance may be unstable over billions of years.While all the planets that have been designed can be considered habitable, their fauna and flora may be very different.
Spohn, T. and Hoening, D: Land/Ocean Surface Diversity on Earth-Like Planets (Exo): Implications for Habitability, Europlanet Science Congress 2022, Granada, Spain, Sep 18–23 2022, EPSC2022-506, 2022.