by Scientists have learned more about the violent processes that tear atmospheres from planets, discovering that squashing and eruptions by a parent star can contribute to this process.
The research, conducted by Guo Jianheng of the Yunnan Observatory of the Chinese Academy of Sciences, could help astronomers better determine which extrasolar planets, or “exoplanets,” to take a closer look at as they expand their search for life outside the solar system .
There are several ways in which planets can lose their atmosphere to space, including the upper atmosphere leaving the planet as a whole, known as “hydrodynamic escape.” This process is thought to be more intense than the process by which the planets of our solar system eject particles into space today, through “hydrodynamic escape,” which causes a planet to lose mass and also affects its climate and, therefore, on their locality.
Jianheng’s simulated atmosphere loss from a low-mass exoplanet. Jianheng focused in particular on the mechanism of hydrodynamic escape atmosphere loss and proposed a new classification method that can be used to understand this and other escape processes.
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Although it no longer occurs for the inner planets around the sun, in the early solar system, hydrodynamic atmospheric escape may have actually occurred for planets such as Venus and Earth. If the process had continued, our planet might have been left with only a thin, mostly waterless atmosphere similar to what we see around our planetary neighbor, Mars.
That means that the escape of a hydrodynamic atmosphere could help to find out why Earth is able to support life, but Mars and Venus are not.
Although hydrodynamic atmospheric escape is not currently ripping out atmospheres in the solar system, astronomers have used space and ground-based telescopes to determine that these processes are indeed occurring around exoplanets located close to their hosts -stars.
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Jianheng performed computer simulations of low-mass exoplanets, which showed that those with hydrogen-rich atmospheres may suffer from hydrodynamic atmospheric escape as a result of their internal energy processes.
This energy appears as internal heat and is generated by the tidal forces that squash and squeeze the planet — forces caused by the gravity of its parent stars and the bombardment of intense ultraviolet radiation from those stars. Sometimes, these forces can even deform planets into ovoid shapes.
Previously, modeling was used to understand the physical mechanisms driving hydrodynamic escape, but these models were complex and often led to vague conclusions.
Jianheng, on the other hand, suggests that the physical parameters needed to classify the mechanisms behind hydrodynamic escape are simple. All you have to do is think about the characteristics of the planets and stars in question, according to the researcher, such as their masses, radii, and the orbital separation between the planet and its star.
Jianheng’s simulations showed that those with low masses and large radii could cause atmospheric escape for more “glow” and less dense exoplanets. A ratio of the planet’s internal energy to its gravitational potential energy, known as the “Jeans parameter,” could be used to determine whether a planet would succeed in escaping its atmosphere. The smaller the Jeans parameter, the more likely atmospheric escape is.
For planets unable to undergo hydrodynamic escape due to high internal energies, Jianheng found that a modified Jeans parameter accounting for tidal forces generated by stars could determine and distinguish the roles of these forces and ultraviolet radiation extreme in driving atmospheric escape.
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The simulation also revealed that low-mass planets with high gravitational potential result in slower hydrodynamic atmospheric escape due to increased distance between a planet and its star, as well as the lower radiation such a world would produce.
The findings could help scientists better determine how the atmosphere of low-mass planets changes over time, helping to paint a better picture of the habitability of these worlds.
This research was published on May 9 in the journal Nature Astronomy.
