Encyclopedia of Astrobiology

Living Edition
| Editors: Muriel Gargaud, William M. Irvine, Ricardo Amils, Henderson James Cleaves, Daniele Pinti, José Cernicharo Quintanilla, Michel Viso

Hydrodynamic Escape

  • Francis Albarede
Living reference work entry
DOI: https://doi.org/10.1007/978-3-642-27833-4_4024-5


The term hydrodynamic escape refers to the removal of gas from the atmosphere of a planet possessing a strong gravity field by the viscous drag of an escaping lighter gas, typically hydrogen. This phenomenon may explain why some planetary atmospheres are depleted in oxygen, nitrogen, and heavier noble gases, such as xenon.


When atmospheric temperature is high enough, the thermal agitation of gas molecules may be strong enough for some gaseous species to leave the gravity field of the planet. For a planetary body with radius Rp, Jean’s escape velocity is obtained by equating the kinetic and potential energy and is equal to \( \sqrt{2GM/{R}_p} \)


Gravity Field Thermal Velocity Viscous Drag Planetary Atmosphere Escape Velocity 
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References and Further Reading

  1. Hunten DM, Pepin RO, Walker JCG (1987) Mass fractionation in hydrodynamic escape. Icarus 69:532–549CrossRefADSGoogle Scholar
  2. Pepin RO (1991) On the origin and early evolution of terrestrial planet atmospheres and meteoritic volatiles. Icarus 92:2–79CrossRefADSGoogle Scholar

Copyright information

© Springer-Verlag Berlin Heidelberg 2014

Authors and Affiliations

  1. 1.Ecole Normale Supérieure de LyonLyonFrance