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M. H. Burger, R. E. Johnson (University of Virginia)
Recently reported Galileo observations coupled with Cassini measurements during its Jupiter flyby are suggestive of the presence of a water product component of Europa's extended cloud. Lagg et al. (2003) reported the depletion of protons with pitch angle of 90 degrees near Europa which suggests the presence of an equatorially confined cloud of neutral gas. Mauk et al. (2003) detected energetic neutrals resulting from charge exchange between protons and atomic or molecular neutrals in the Europa cloud.
Models of the previously detected sodium component of this cloud (Brown and Hill 1996, Leblanc et al. 2002) by Burger and Johnson (2004) predict that the cloud morphology is significantly different from the morphology of the Io neutral cloud. Due to differences in the radial variations in the magnetospheric plasma at each satellite, the Io cloud is predominately a leading cloud while the Europa cloud is a trailing cloud expanding radially outward from Jupiter.
We present models of the molecular and atomic oxygen clouds formed from water dissociation products escaping from Europa's surface and atmosphere and compare with the Galileo and Cassini observations. These studies use recent models of Europa's atmosphere (Shematovich et al. 2004) and an empirical description of the Io plasma torus (described in Burger 2003) to estimate the large scale distribution of neutrals escaping from Europa. In addition, we discuss the effects of the variable plasma environment on observable oxygen emissions. This work has been supported by grants from NASA's Planetary Atmospheres Program.
References: Brown, M.E. and Hill, R.E. Nature, 380, 229, 1996. Burger, M.H. Ph.D. Thesis, University of Colorado, 2003. Burger, M.H., Johnson, R.E. Icarus, in press, 2004. Lagg, A., Krupp, N., Woch, J., Williams, D.J. GRL, 30, 10-1, 2003. Leblanc, F., Johnson, R.E., Brown, M.E. Icarus, 159, 132, 2002. Mauk, B.H., et al. Nature, 421, 920, 2003. Shematovich, V. I., Johnson, R.E., Cooper, J.F. Wong, M.C, Icarus, submitted, 2004.
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Bulletin of the American Astronomical Society, 36 #4
© 2004. The American Astronomical Soceity.