HR: 09:15h
AN: P51E-06    [Abstracts]
TI: Composition and Detection of Europa's Sputter-Induced Atmosphere
AU: * Johnson, R E
EM: rej@virginia.edu
AF: University of Virginia, Wilsdorf Hall, Charlottesville, VA 22904, United States
AU: Burger, M H
EM: matthew.burger@gsfc.nasa.gov
AF: NASA/GSFC, Greenbelt Rd, GreenBelt, MD 20771, United States
AU: Cassidy, T A
EM: tac2z@virginia.edu
AF: University of Virginia, Wilsdorf Hall, Charlottesville, VA 22904, United States
AU: Leblanc, F
EM: francois.leblanc@aerov.jussieu.fr
AF: Service Aeronomy, 4 place Jussieu, Paris, BP 102, France
AU: Marconi, M L
EM: marconi@freshpond.org
AF: Prisma Basic Research, 1625 Buffalo Ave, Niagra Falls, NY 14303,
AU: Smyth, W H
EM: wsmyth@aer.com
AF: AER, 131 Hartwell Ave, Lexington, MA 02421, United States
AB: Europa has an extremely tenuous atmosphere that appears to be marginally collisional, so that species ejected from the surface with sufficient energy have a high probability of escape. Such an atmosphere is often referred to as a surface boundary-layer atmosphere. That is, as at Mercury, the Moon and Ganymede, the interaction of the ambient gas with the surface determines the composition, local column density, and morphology of the atmosphere. Since gas phase species are often more readily identified both in situ and by remote sensing, Europa's atmosphere is of interest as an extension of Europa's surface. Since Europa is imbedded in the Jovian magnetosphere and is not protected from the solar EUV flux, radiolytic, photolytic and stimulated desorption processes populate the atmosphere with atoms and molecules ejected from Europa's surface. These processes are often lumped together using the words ‘sputter-produced' atmosphere. Early laboratory sputtering data by Brown, Lanzerotti and co-workers were used to predict the principal atmospheric component, O2, and its average column density. Since H2 loss accompanies the formation and ejection of O2 from ice and H2 escapes readily, the atmospheric formation process also efficiently populates the Jovian magnetosphere. In fact the extension of Europa's atmosphere as a gas torus gravitationally bound to Jupiter and only perturbed by Europa contains more of Europa's ejected surface material than the gravitationally bound atmosphere. In addition to O2, Na and K have been identified. Here we review the modeling of Europa's sputter produced atmosphere and ionosphere. Our principal interest is in the morphology of the atmosphere and the relationship between the composition and Europa's local surface composition. The possibility of detection by an orbiting spacecraft is considered as is the relevance of such detections to Europa's putative subsurface ocean.
DE: 6005 Atmospheres (1060)
DE: 6040 Origin and evolution
SC: Planetary Sciences [P]
MN: 2007 Fall Meeting