Astronomy and Astrophysics – Astrophysics
Scientific paper
Dec 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufm.p13d..04j&link_type=abstract
American Geophysical Union, Fall Meeting 2009, abstract #P13D-04
Astronomy and Astrophysics
Astrophysics
[0325] Atmospheric Composition And Structure / Evolution Of The Atmosphere, [0328] Atmospheric Composition And Structure / Exosphere, [0358] Atmospheric Composition And Structure / Thermosphere: Energy Deposition
Scientific paper
The atmospheres of planets and planetary satellites are typically imbedded in space plasmas. Depending on the interaction with the induced or intrinsic fields energetic ions can have access to the thermosphere and the corona affecting their composition and thermal structure and causing loss to space. These processes are often lumped together as ‘atmospheric sputtering’ (Johnson 1994). In this talk I will review the results of simulations of the plasma bombardment at a number of solar system bodies and use those data to describe the effect on the upper atmosphere and on escape. Of considerable recent interest is the modeling of escape from Titan. Prior to Cassini’s tour of the Saturnian system, plasma-induced escape was suggested to be the dominant loss process, but recent models of enhanced thermal escape, often referred to as ‘slow hydrodynamic’ escape, have been suggested to lead to much larger Titan atmospheric loss rates (Strobel 2008; Cui et al. 2008). Such a process has been suggested to be active at some point in time on a number of solar system bodies. I will present hybrid fluid/ kinetic models of the upper atmosphere of certain bodies in order to test both the plasma-induced and thermal escape processes. Preliminary results suggest that the loss rates estimated using the ‘slow hydrodynamic’ escape process can be orders of magnitude too large. The implications for Mars, Titan and Pluto will be discussed. Background for this talk is contained in the following papers (Johnson 2004; 2009; Chaufray et al. 2007; Johnson et al. 2008; 2009; Tucker and Johnson 2009). References: Chaufray, J.Y., R. Modolo, F. Leblanc, G. Chanteur, R.E. Johnson, and J.G. Luhmann, Mars Solar Wind interaction: formation of the Martian corona and atmosphric loss to space, JGR 112, E09009, doi:10.1029/2007JE002915 (2007) Cui, J., Yelle, R. V., Volk, K. Distribution and escape of molecular hydrogen in Titan's thermosphere and exosphere. J. Geophys. Res. 113, doi:10.1029/2007JE003032 (2008) Johnson, R.E. Plasma-induced Sputtering of an Atmosphere. in Space Science Rev. 69, 215-253 (1994). Johnson, R.E., The Magnetospheric Plasma-Driven Evolution of Satellite Atmospheres, Astrophys. J. 609: L99-L102 (2004). Johnson, R.E., M.R. Combi, J.L. Fox, W-H. Ip, F. Leblanc, M.A. McGrath, V.I. Shematovich, D.F. Strobel, J.H. Waite Jr, Exospheres and Atmospheric Escape, Chapter in Comparative Aeronomy, Ed. A. Nagy, Space Sci. Rev. 139: 355-397, DOI 10.1007/s11214-008-9415-3 (2008) Johnson, R.E., Sputtering and heating of Titan's upper atmosphere, Phil. Trans. R. Soc. A 367, 753-771, doi:10.1098/rsta.2008.0244 (2009) Johnson, R.E., O.J. Tucker, M. Michael, E.C. Sittler, H.T. Smith, D.T. Young, and J.H. Waite, Mass Loss Processes in Titan's Upper Atmosphere, Springer-Verlag in press (2009) Strobel, D. F. Titan's hydrodynamically escaping atmosphere. Icarus 193, 588—594 (2008)
Cassidy Timothy A.
Ewrin J.
Johnson Robert E.
LeBlanc Francis
Tucker Orenthal J.
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