FUV emissions on Io: Role of Galileo‐observed field‐aligned energetic electrons

Discovery of Soft X‐Ray Emission from Io, Europa, and the Io Plasma Torus

“…Approximately 5 keV H + , 40 keV O + , and 60 keV S + ions penetrate an atmosphere with a column density of 10 17 SO 2 molecules/cm 2 (Lanzerotti et al 1982); these limits fall between 1 and 10 keV for a column density of 10 16 SO 2 molecules/cm 2 . For comparison, electrons with energy greater than about 10 keV penetrate a column density of 10 17 SO 2 molecules/cm 2 (Michael and Bhardwaj 2000). The integrated ion energy flux at Europa for H, O, and S above 10 keV , Cooper et al 2001) is ∼ 10 10 keV/s-cm 2 .…”

Photochemistry of a Volcanically Driven Atmosphere on Io: Sulfur and Oxygen Species from a Pele-Type Eruption

“…The possibility that electron impact could be occurring at night is clearly demonstrated in Galileo eclipse and nighttime images of Io (e.g., McEwen et al 1998a, Geissler et al 1999b in which visible gas emissions are observed both in localized regions associated with known volcanic centers and in broad regions of diffuse emission across the whole disk. The emission is believed to be caused by electron impact of SO 2 and/or SO (prominent at blue wavelengths), atomic oxygen (prominent at red and green wavelengths), and atomic sodium (prominent at green wavelengths) (see Bouchez et al 2000, Geissler et al 1999b; see also the theoretical descriptions of the "equatorial spots" and other emissions, e.g., Retherford et al 2000a, Saur et al 2000, Michael and Bhardwaj 2000. The fact that Io's disk-integrated brightness decreases with time after Io has passed behind Jupiter's shadow in these images suggests that SO 2 might be condensing (and the atmosphere collapsing) as the surface temperature drops (Geissler et al 1999b).…”

$\mathsf{H^+}$ + H(1s) collisions at intermediate impact velocities as a new source of UV and VUV radiation

“…Thus, for UV and VUV could be important the radiative charge exchange processes of protons from the solar wind with oxigen atoms (almost resonant case), as well as with nitrogen atoms in the upper layers of Earth's atmosphere. Similar example is the interaction of the upper layers of Iovian atmosphere with streams of weakly ionized plasma, produced by volcanic activities of its satellite Io (Michael 2003;Michael & Bhardwaj 2000). The obtained results suggest that the ion-atom collision processes with impact velocities at 100 km s −1 can be important.…”