1. ESTIMATION OF THE EFFICIENCY OF DIFFERENT SPACE WEATHER PROCESSES AT JUPITER’S EUROPA MOON A. Lucchetti, C. Plainaki, G. Cremonese, A. Milillo, T. Cassidy, X. Jia, V. Shematovich The reactions in the exosphere of Jupiter’s moon Europa are dominated by plasma-neutral interactions leading to the effective loss of the moon’s neutral population. From Bagenal et al. (2015)

2. LOSS PROCESSES  Estimate the H 2 O, O 2, and H 2 loss rates due to plasma-neutral interactions -using the updated plasma conditions at the moon’s vicinity, calculated recently by Bagenal et al. (2015) From Bagenal et al. (2015) density profile of pick up ions of different species for altitudes up to 200 km from the surface (Sittler et al., 2013)  Calculate the role of the interactions between the planetary ions and the neutral populations in the loss of exospheric species -using the ionosphere and pick up ions properties from Sittler et al. (2013)

3. ELECTRON-NEUTRAL REACTIONS dissociation and ionization ION-NEUTRAL INTERACTIONS Charge-exchange for three ion populations: -The S ++ and O + ions in the plasma -the pick-up ions -the ionosphere ions H 2 O exosphere The dominant loss is due to electron impact dissociation, with a rate equal to 3.31 x 10 -6 s -1 (median plasma conditions, cold plasma electron population) H 2 exosphere the dominant loss process is electron impact ionization (leading to the production of H 2 +, median plasma conditions) and electron impact dissociation ( high plasma density and low plasma temperature). Both processes have rates equal to 3.55 x 10 -6 s -1 O 2 exosphere The dominant loss is due to charge-exchange reactions between the ionospheric O 2 + and exospheric O 2 molecules with a rate, equal to ~ 15 x 10 -6 s -1

4. to the Sun to Jupiter The O 2 exosphere as given by the EGEON model (Plainaki et al., 2012, 2013) is considered, examining two different configurations between Jupiter, Europa and the Sun: APPLICATION: Calculation of the volume integrated O 2 loss rates (B) Subsolar point coincides with the trailing hemisphere apex spatially averaged O 2 col.density ~1.1 x 10 19 m -2 (A) Subsolar point coincides with the leading hemisphere apex spatially averaged O 2 col.density ~ 2.7 x 10 18 m -2 to the Sun to Jupiter Plainaki et al., PSS, 2013 AB Lucchetti et al., 2015 under review

5.  For both H 2 O and H 2 exospheres, the loss is very variable depending on the position of Europa with respect to the JPS. The cold plasma electron population is the main responsible for H 2 O and H 2 loss.  For the O 2 exosphere, we find the O 2 - O 2 + charge-exchange process may have a dominant role in the exosphere loss, contrary to what it had been previously thought.  The O 2 - O 2 + charge exchange rate is in the range (13 -51) x 10 26 s -1 depending also on the configuration between Europa, Jupiter and the Sun. CONCLUSION  The estimation of the efficiency of the dominant interactions at Europa can be used as a starting point in future modeling studies of the moon's environment. The work in this paper has been performed in the context of the activities of the ISSI International Team #322: "Towards a global unified model of Europa's exosphere in view of the JUICE mission” http://www.issibern.ch/teams/exospherejuice/".