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date: 26 June 2022

Hot Planetary Coronaslocked

Hot Planetary Coronaslocked

  • Valery I. ShematovichValery I. ShematovichInstitute of Astronomy, Russian Academy of Sciences
  •  and Dmitry V. BisikaloDmitry V. BisikaloInstitute of Astronomy, Russian Academy of Sciences

Summary

The uppermost layers of a planetary atmosphere, where the density of neutral particles is vanishingly low, are commonly called exosphere or planetary corona. Since the atmosphere is not completely bound to the planet by the planetary gravitational field, light atoms, such as hydrogen and helium, with sufficiently large thermal velocities can escape from the upper atmosphere into interplanetary space. This process is commonly called Jeans escape and depends on the temperature of the ambient atmospheric gas at an altitude where the atmospheric gas is virtually collisionless. The heavier carbon, nitrogen, and oxygen atoms can populate the coronas and escape from the atmospheres of terrestrial planets only through nonthermal processes such as photo- and electron-impact energizing, charge exchange, atmospheric sputtering, and ion pickup.

The observations reveal that the planetary coronae contain both a fraction of thermal neutral particles with a mean kinetic energy corresponding to the exospheric temperature and a fraction of hot neutral particles with mean kinetic energy much higher than that expected for the exospheric temperature. These suprathermal (hot) atoms and molecules are the direct manifestation of the nonthermal processes taking place in the atmospheres. These hot particles populate the hot coronas, take a major part in the atmospheric escape, produce nonthermal emissions, and react with the ambient atmospheric gas, triggering the hot atom chemistry.

Subjects

  • Extrasolar Planets and Systems
  • Planetary Atmospheres and Oceans
  • Small Bodies

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