On May 9, the latest research conducted by Guo Jianheng, a researcher at the Yunnan Astronomical Observatory of the Chinese Academy of Sciences, was published in "Nature Astronomy." This study reveals the various driving mechanisms affecting the intense atmospheric escape process on low-mass exoplanets known as "fluid atmospheric escape," and proposes a new, more accurate classification method.
Research Illustration. Image provided by Yunnan Astronomical Observatory
Studying planets beyond our solar system is a hot topic in astronomy. The atmosphere of a planet orbiting a star may escape into space for various reasons. When the upper atmosphere of a planet leaves the planet as a whole in a violent manner, it is known as "fluid atmospheric escape." Compared to the particle behavior escape seen in planets in our solar system, fluid escape processes are much more intense.
Guo Jianheng explains that fluid atmospheric escape may have occurred in the early stages of planets in our solar system. If Earth had lost its entire atmosphere in a fluid dynamic escape in its early stages, it might have ended up as desolate as Mars. Today, such intense escape mechanisms no longer exist on Earth and other planets in our solar system.
However, scientists have discovered through observations from space and ground-based telescopes that fluid escape continues to occur on some exoplanets closer to their host stars. Fluid atmospheric escape not only alters a planet's mass but also affects its climate and habitability.
"Fluid atmospheric escape on low-mass exoplanets can be driven by planetary internal energy, stellar tidal forces, or extreme ultraviolet radiation from the star, either individually or in combination," Guo Jianheng told the Chinese Science Bulletin.
Previously, researchers had to rely on complex calculations to determine the physical mechanisms driving fluid escape on a planet, and the conclusions were often unclear.
In a recent paper, researchers were able to classify the mechanisms of fluid escape on low-mass planets using only basic physical parameters of the star and planet, such as mass, radius, and orbital distance.
The study found that on low-mass, large-radius planets, atmospheric escape can be driven by sufficient internal energy or high temperatures. Therefore, using the "Kings parameter," which represents the ratio of planetary internal energy to potential energy, can determine whether such escape occurs.
For planets where internal energy cannot drive atmospheric escape, the study introduced an improved "Kings parameter" by considering stellar tidal forces. With this improved parameter, researchers accurately distinguished the roles of stellar tidal forces and extreme ultraviolet radiation in driving atmospheric escape.
Furthermore, the study revealed that planets with high gravitational potential and low stellar radiation are more likely to experience slow fluid atmospheric escape, while other planets primarily undergo rapid fluid escape.
Han Zhanwen, academician of the Chinese Academy of Sciences and researcher at the Yunnan Astronomical Observatory, pointed out, "This study cleverly uses basic physical parameters of star-planet systems to clearly classify the atmospheric escape mechanisms of planets, advancing our understanding of planetary atmospheric escape and providing a theoretical basis for future research on planetary habitability and atmospheric evolution."
Guo Jianheng believes that the results of this study can not only help us understand how a planet's atmosphere evolves over time but also have potential applications in exploring the evolution and origins of low-mass planets. As humanity delves deeper into the exploration of potentially habitable exoplanets in the universe, these findings will aid in better understanding the environments and evolutionary processes of these distant worlds.
Related paper information: http://doi.org/10.1038/s41550-024-02269-w
