Continents may be the key to whether exoplanets can host life

Each year, the number of planets discovered orbiting other stars continues to grow, and many of them appear similar to Earth in size and mass.

Yet as the latest advances in astronomy – such as the James Webb Space Telescope (JWST) – allow astronomers to study these distant worlds in ever greater detail, there is a particularly pressing unanswered question: how many of them could realistically support. the life?

Part of the key to answering this question lies in analyzing the chemical compositions of the atmospheres of exoplanets. Astronomers can do this by collecting the chemical signatures imprinted on the spectra of starlight after it has passed through the atmosphere of an exoplanet.

These factors will be crucial for astronomers to consider in determining whether a newly discovered exoplanet can be habitable.

In July 2022, such a spectrum was released along with the first color images taken by the JWST, which clearly show the presence of water in the atmosphere of the exoplanet WASP-96 b.

But the chemical composition is not the only factor that affects the habitability of a planet. Just as we see on Earth, planetary climates are deeply interconnected with the configurations of their continents and oceans. This arrangement affects their temperatures and the ways in which air and water move around their atmospheres.

These factors will be crucial for astronomers to consider in determining whether a newly discovered exoplanet can be habitable. However, because even the JWST is not powerful enough to detect details on the surfaces of exoplanets, such assessments cannot be made directly.

Virtual Continents: To explore the matter in more detail, a team of researchers in Canada looked at the climates of virtual exoplanets, which they generated in computer simulations.

In their study, Evelyn Macdonald and colleagues at the University of Toronto studied a series of simulated Earth-like planets that were “tidal stuck” with their host stars: rotating so that one side is permanently facing the star. , while the other stays permanently night.

All the planets showed similar patterns in air circulation.

To simplify their calculations, the researchers gave their planets a circular continent surrounded by the ocean, placed square in the center of its diurnal side; or a circular ocean surrounded by land. By varying the size of these circles, they could fine-tune the proportion of land and sea, allowing them to estimate the effects of continental configurations on each planet’s climate.

Regardless of the configuration of the earth, Macdonald’s team found that all of their planets exhibited similar patterns in air circulation. Moisture-laden air rises to the hottest spot on the planet, which is at the center of its circular continent or ocean, then moves to the frozen night side, falls back to the surface, and backs up to the circle, collecting moisture in the processes.

Similar patterns can also be found on Earth: warm, humid air rises to the equator, then moves to colder polar regions. The dry air then falls back to Earth in arid regions such as the Sahara and the Outback, which surround the water-rich tropics.

Variable climates: Beyond these similarities, the climates of the virtual planets varied widely as Macdonald’s team altered the fraction of their surface occupied by the mainland.

Regardless of the configuration of their continents, the diurnal sides of the planets became increasingly hot as their land masses became larger, while the night sides became colder: with average surface temperatures ranging up to 20 ° C.

The temperature and water content of a planet’s atmosphere are not necessarily sufficient to tell how its climate will behave.

Macdonald and his colleagues found that the amount of ice-free ocean on each planet’s day side determines how much water vapor a planet can have in its atmosphere. While planets with a high percentage of ice-free earth had drier climates, those with larger, ice-free oceans contained more abundant moisture, producing cloudier and wetter climates.

The team also explored how these patterns varied with different levels of atmospheric carbon dioxide. They found that although their planets typically became warmer and wetter with greater amounts of greenhouse gases, the same climate patterns as before still emerged as the arrangement of each planet’s continent varied.

Studying real planetary atmospheres: Overall, the simulations helped Macdonald’s team get a clearer picture of the climates that can be found on Earth-like exoplanets.

They ultimately show that even though the temperature and water content of a planet’s atmosphere can be studied in detail, this isn’t necessarily enough for astronomers to tell how its climate will behave.

As observations with the JWST promise to add a whole new dimension to the already exciting field of exoplanet discovery, the result could provide important insights for astronomers aiming to determine if life might indeed be out there on newly discovered exoplanets.

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