Modeling Atmospheric Escape Workshop - Spring 2012
University of Virginia: Charlottesville, Virginia

  February 27-28, 2012

Organizer/Host: Dr. R. E. Johnson, rej@virginia.edu
Co-Host:            Dr. Francois Leblanc, francois.leblanc@latmos.ipsl.fr

Contact:
Justin Erwin,   jte2c@virginia.edu

 Ms. M. Liu,         ml7q@virginia.edu

Attendance by Invitation  (no workshop fee)

DESCRIPTION
All planetary atmospheres are permanently evaporating. Since escape influences the chemical composition and thermal structure of the upper atmosphere, as well as the ability to retain a sizable atmosphere, as at Pluto and close in exoplanets, accurate simulations are required. Although atmospheric escape and the kinetic theory of gases has been studied for years, the transition from continuum models for escape to molecular flow, which is inevitable at high altitudes, remains largely unexplored.

Simulations of planetary atmosphere often use fluid dynamics with almost arbitrary boundary conditions at the exobase or infinity. This is also the case when using diffusion equations with escape of light species at the upper boundary as a parameter for fitting to density data. Although such continuum models are adequate in many instance, it has recently been they can fail dramatically. With New Horizon on its way to Pluto, Maven soon to be launched to Mars, Cassini observing Titan and the extensive new telescopic data on extrasolar planets, accurate descriptions of molecular loss from planetary bodies are needed. It is exciting that we now have the ability to develop models tested against accurate in situ spacecraft measurements and then apply that knowledge to the now growing data base of exoplanets that span a large range of masses, radii and heating rates.

At the workshop, to be held at the University of Virginia Feb 27-28, 2011, we will discuss methods for modeling escape processes at bodies for which we have or will have in situ data, and in what instances that understanding can be translated to modeling escape from and evolution of early terrestrial atmospheres or exoplanet atmospheres which are only observed remotely. We will try to define under what conditions various escape processes are important on a variety of planets and how well we agree on modeling these processes.

ISSUES TO BE ADDRESSED
When are molecular kinetic models of escape required ?
When are continuum models (hydrodynamics with or without diffusion) adequate ?
Is the a criterion for transonic flow using the size of the Jeans parameter at the nominal exobase valid ?
When are simple but useful approximations, like energy limited escape, valid ?
How can the modeling of nonthermal processes be incorporated ?
Since thermal equilibrium can break down well below the nominal exobase when molecules with very different masses are present, how does one model diffusive loss ?