Europa's Atmosphere and Magnetospheric Implications

Details Europa's Atmosphere and Magnetospheric Implications Europa's Atmosphere and Magnetospheric Implications

Nov 2004

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004dps....36.0904s&link_type=abstract

American Astronomical Society, DPS meeting #36, #09.04; Bulletin of the American Astronomical Society, Vol. 36, p.1083

Astronomy and Astrophysics

Astronomy

1

Scientific paper

The presence of a tenuous atmosphere on Europa consisting of a column of (2-15) x 1014 cm-2 of O2 has been inferred from the measurements of OI 1304 Å emissions (Hall et al., Nature 373, 677-679, 1995 and Ap. J. 499, 475-481, 1998). Model calculations (Shematovich and Johnson, Adv. Space Res. 27, 1881-1888, 2001 and Shematovich et al., preprint, 2004) have since elucidated the structure of the oxygen atmosphere and shown that such columns are obtainable for the expected sputtering rates at Europa. Hydrogen, however, is also produced in substantial amounts by sputtering of Europa's largely H2O surface by energetic heavy ions and to a lesser extent by sublimation of H2O. We have recently calculated (Marconi and Smyth, EOS 85, JA308, 2004) the spatial distributions of the water group species (H2, H, O2, O, H2O, OH) in Europa's atmosphere using a 2-D hybrid fluid/kinetic model (Marconi, Icarus 166, 410-424, 2003). We find that while oxygen dominates near the surface, hydrogen is the principal species at higher altitudes. We also find that hydrogen is the most abundant of the escaping species, and hence, an important source for the Europa neutral gas tori about Jupiter. The spatial structure of the most abundant Europa neutral tori and their plasma sources have therefore been calculated with the AER Neutral Cloud Model (Smyth and Combi, Ap. J. 328, 888-918, 1988). We find that the abundances of the neutral clouds of Europa are comparable to those for Io. These calculations will be presented, and some implications of Europa's neutral clouds on the thermal plasma, energetic plasma, and the production of energetic neutral atoms in the plasma torus as measured by the Voyager (Bagenal, JGR 99, 11,043-11,062, 1994), Galileo (Mauk et al., JGR 109, A09S12 doi:10.1029/2003JA010270, 2004), and Cassini (Mauk et al., Nature 421, 920-922, 2003) spacecrafts will be discussed.

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