User:Ceholloway45/Atmospheric Escape of Exoplanet Atmospheres

=== Article body ===

=== Article body ===

As of April 2026, there are 6,160 confirmed exoplanets, with over 7,000 yet-to-be confirmed [nasa exoplanet archive]. By combining various methods, such as the transiting and radial velocity, it is possible to derive estimates for these planets. The bulk of  these planets are Super-Earths and sub-Neptunes, types with no Solar System analogs [Seager 2010]. Additionally, there are few planets, with radii between 1.3 - 2.5 $R_{\Earth}$, between these types. This gap is known as the "radius valley." Recently, it has been proposed that terrestrial planets could obtain their size through atmospheric escape [fulton 2017].

As of April 2026, there are 6,160 confirmed exoplanets, with over 7,000 yet-to-be confirmed [nasa exoplanet archive]. By combining various methods, such as the transiting and radial velocity, it is possible to derive estimates for these planets. The bulk of these planets are Super-Earths and sub-Neptunes, types with no Solar System analogs [1]. Additionally, there are few planets, with radii between 1.3 - 2.5 $R_{\Earth}$, between these types. This gap is known as the "radius valley." Recently, it has been proposed that terrestrial planets could obtain their size through atmospheric escape [3].

Atmospheres are hypothesized to be a collection of atoms and molecules that exist in a quasi-hydrostatic state. When incident short-wave radiation heats the thermosphere, the upper thermosphere becomes isothermic through conduction. The upper thermosphere is separated by the exobase-level. This is the boundary that separates the collision-dominated and collision-less regions. At certain temperatures above the exobase, collision-less region, light atmospheric species can become energetic enough to escape the gravitational potential of the planet, escaping into space [Lammer 2013]. This process is known as the jeans escape. This process can only occur within the collision-less region. The region below the exobase, a collision-dominated region, is in hydrostatic equilibrium. However, in conditions of intense extreme Ultraviolet and X-rays, the bulk gasses within the collision-less region can become energetic enough to cause hydrodynamic outflows, similar to Parker winds (Hazra 2025). Atmospheric escape can occur in two categories: non-thermal and thermal. The two processes mentioned earlier, Hydrodynamic and Jean escape, are two major thermal atmospheric escape mechanisms that may be responsible for the "radius valley" gap.

Atmospheres are hypothesized to be a collection of atoms and molecules that exist in a quasi-hydrostatic state. When incident short-wave radiation heats the thermosphere, the upper thermosphere becomes isothermic through conduction. The upper thermosphere is separated by the exobase-level. This is the boundary that separates the collision-dominated and collision-less regions. At certain temperatures above the exobase, collision-less region, light atmospheric species can become energetic enough to escape the gravitational potential of the planet, escaping into space [Lammer 2013]. This process is known as the jeans escape. This process can only occur within the collision-less region. The region below the exobase, a collision-dominated region, is in hydrostatic equilibrium. However, in conditions of intense extreme Ultraviolet and X-rays, the bulk gasses within the collision-less region can become energetic enough to cause hydrodynamic outflows, similar to Parker winds (Hazra 2025). Atmospheric escape can occur in two categories: non-thermal and thermal. The two processes mentioned earlier, Hydrodynamic and Jean escape, are two major thermal atmospheric escape mechanisms that may be responsible for the "radius valley" gap.

=== References ===

=== References ===

* '''Seager, Sara; Deming, Drake (2010). “Exoplanet Atmospheres.” ''Annual Review of Astronomy and Astrophysics'', 48: 631–672. doi:10.1146/annurev-astro-081309-130837. https://ui.adsabs.harvard.edu/abs/2010ARA&A..48..631S'''

# '''Seager, Sara; Deming, Drake (2010). “Exoplanet Atmospheres.” ''Annual Review of Astronomy and Astrophysics'', 48: 631–672. doi:10.1146/annurev-astro-081309-130837. https://ui.adsabs.harvard.edu/abs/2010ARA&A..48..631S'''

* '''NASA Exoplanet Science Institute (2024). ''NASA Exoplanet Archive''. California Institute of Technology. Retrieved 20 April 2026, from''' https://exoplanetarchive.ipac.caltech.edu/ '''(exoplanetarchive.ipac.caltech.edu in Bing)'''

# '''NASA Exoplanet Science Institute (2024). ''NASA Exoplanet Archive''. California Institute of Technology. Retrieved 20 April 2026, from''' https://exoplanetarchive.ipac.caltech.edu/ '''(exoplanetarchive.ipac.caltech.edu in Bing)'''

* '''ulton, Benjamin J.; Petigura, Erik A.; Howard, Andrew W.; Isaacson, Howard; Marcy, Geoffrey W.; Cargile, Phillip A.; Hebb, Leslie; Weiss, Lauren M.; Johnson, John Asher; Morton, Timothy D.; Sinukoff, Evan; Crossfield, Ian J. M.; Hirsch, Lea A. (2017). “The California‑Kepler Survey. III. A Gap in the Radius Distribution of Small Planets.” ''The Astronomical Journal'', 154 (3): 109. doi:10.3847/1538‑3881/aa80eb.'''

# '''Fulton, Benjamin J.; Petigura, Erik A.; Howard, Andrew W.; Isaacson, Howard; Marcy, Geoffrey W.; Cargile, Phillip A.; Hebb, Leslie; Weiss, Lauren M.; Johnson, John Asher; Morton, Timothy D.; Sinukoff, Evan; Crossfield, Ian J. M.; Hirsch, Lea A. (2017). “The California‑Kepler Survey. III. A Gap in the Radius Distribution of Small Planets.” ''The Astronomical Journal'', 154 (3): 109. doi:10.3847/1538‑3881/aa80eb.'''

* '''Perryman, Michael (2018). ''The Exoplanet Handbook'' (2nd ed.). Cambridge University Press. ISBN 978‑1‑108‑42234‑3.'''

# '''Perryman, Michael (2018). ''The Exoplanet Handbook'' (2nd ed.). Cambridge University Press. ISBN 978‑1‑108‑42234‑3.'''

* '''Lammer, Helmut (2013). ''Origin and Evolution of Planetary Atmospheres: Implications for Habitability''. Springer. ISBN 978‑3‑642‑32086‑6.'''

# '''Lammer, Helmut (2013). ''Origin and Evolution of Planetary Atmospheres: Implications for Habitability''. Springer. ISBN 978‑3‑642‑32086‑6.'''

# '''Hazra, Gopal (2025). “Atmospheric Escape Processes of Exoplanets.” ''Annual Review of Earth and Planetary Sciences'', 53: 1–34. doi:10.1146/annurev-earth-090124‑015432.'''

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