Molecular-Kinetic Simulations of Escape from the Ex-Planet and Exoplanets: Criterion for Transonic Flow

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dc.contributor.author Johnson, Robert E.
dc.contributor.author Volkov, Alexey N.
dc.contributor.author Erwin, Justin T.
dc.date.accessioned 2018-10-12T20:03:41Z
dc.date.available 2018-10-12T20:03:41Z
dc.date.issued 2013-12-06
dc.identifier.citation Johnson, R. et al. (2013): Molecular-Kinetic Simulations of Escape from the Ex-Planet and Exoplanets: Criterion for Transonic Flow. The Astrophysical Journal Letters, 768(1). DOI: 10.1088/2041-8205/768/1/L4 en_US
dc.identifier.uri http://ir.ua.edu/handle/123456789/4022
dc.identifier.uri http://iopscience.iop.org/article/10.1088/2041-8205/768/1/L4/meta
dc.description.abstract The equations of gas dynamics are extensively used to describe atmospheric loss from solar system bodies and exoplanets even though the boundary conditions at infinity are not uniquely defined. Using molecular-kinetic simulations that correctly treat the transition from the continuum to the rarefied region, we confirm that the energylimited escape approximation is valid when adiabatic expansion is the dominant cooling process. However, this does not imply that the outflow goes sonic. Rather large escape rates and concomitant adiabatic cooling can produce atmospheres with subsonic flow that are highly extended. Since this affects the heating rate of the upper atmosphere and the interaction with external fields and plasmas, we give a criterion for estimating when the outflow goes transonic in the continuum region. This is applied to early terrestrial atmospheres, exoplanet atmospheres, and the atmosphere of the ex-planet, Pluto, all of which have large escape rates. en_US
dc.format.mimetype application/pdf en_US
dc.subject hydrodynamics en_US
dc.subject molecular processes en_US
dc.subject planets and satellites: atmospheres en_US
dc.title Molecular-Kinetic Simulations of Escape from the Ex-Planet and Exoplanets: Criterion for Transonic Flow en_US
dc.type text en_US


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