DPS 35th Meeting, 1-6 September 2003
Session 2. Io I
Oral, Chair: R. W. Carlson and R. Lopes, Tuesday, September 2, 2003, 10:30am-12:00noon, DeAnza III

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[2.08] Circumplanetary Neutrals from Io and Europa: Magnetospheric Impact and ENA Sources

W.H. Smyth, M.L. Marconi (AAS)

For the Galilean satellites, the distribution and loss of atmospheric gases are shaped by their interactions with the planetary magnetosphere. The gravitational escape of gases from the satellites creates extended neutral clouds on a circumplanetary scale that form asymmetric gas tori about Jupiter, where in the vicinity of the satellite orbit the gas densities are peaked about the satellite’s location. These local and circumplanetary gases supply new pickup ions to the planetary magnetosphere, alter the energetic ion populations and pitch angle distributions, and create energetic neutral atoms (ENAs). Io is known to supply the dominant plasma heavy-ion (O+, O++, S+, S++, S+++) source for the plasma torus and larger planetary magnetosphere. Recent measurements from the NASA Cassini mission by Mauk et al. (Nature 421, 920, 2003) of unexpected copious quantities of ENAs created by the charge exchange of energetic ions and circumplanetary neutrals near Europa’s orbit have suggested that Europa may play a similar role but with an order of magnitude or so smaller gas supply rates than that of Io. The situation for Ganymede and Callisto should be similar in nature, but relevant observations are generally lacking. To investigate the situation, new model calculations for the circumplanetary distribution of neutrals and their instantaneous ion sources that have been undertaken for Io (Smyth and Marconi, (\it Icarus 2003, in press) and Europa will be discussed and compared. These calculations show that the neutral cloud populations of Io and Europa may be comparable although the plasma sources of Io are much larger than those for Europa. The work was supported by the NASA Planetary Atmospheres and Jupiter System Data Analysis Programs.

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Bulletin of the American Astronomical Society, 35 #4
© 2003. The American Astronomical Soceity.