Environmental effects on dust around Europa

Copyright and Moral Rights for the articles on this site are retained by the individual authors and/or other copyright owners. For more information on Open Research Online's data policy on reuse of materials please consult the policies page. Introduction: A dust model has been developed in order to explore the dust environment around Eu-ropa. The dust is composed of five different dust populations: (i) asteroidal and (ii) halo dust populations as part of the interplanetary dust particle (IDP) population [1]; (iii) interstellar dust (ISD) [2]; (iv) the Io stream and [3] (v) ring dust that originate from inside Jupiter's system itself [4-5]. Critically for this study, we have also modelled the dust ejected from the surface of Europa by micrometeoroids impact. Should the ejected dust be a significant proportion of the total dust environment around Europa, a dust analyzer in orbit around Europa could collect some of this dust and hence provide data on the surface composition of Europa. Method: The impacting dust flux (influx) causes the ejection of a certain amount of surface material (outflux) and the relation between the influx and out-flux is determined through the mass yield [6]. In impact experiments and impact modelling in Autodyn hydrocode, the size and velocity distributions of ejected fragments were determined [7]. Assuming that these distributions are independent of the impactor size and velocity, they can be used to model Europa ejecta, allowing the outflux dust to be analysed in detail. The outflux populates the space around Europa, where a small part of the ejecta escapes and the rest eventually falls back to the surface. The model predicts the dust densities of the ejecta outflux at any altitude within Europa's Hill sphere and the dust densities at any altitude can be presented as a size distribution of dust. The results of the present model match the Galileo data (Fig.1-2) collected during several Eu-ropa flybys [8]. Environmental effects. Physical properties at Europa: The uncertainties of the following dust model input parameters were considered: the density of the impacting micrometeoroids [9], the micromete-oroid impact velocity, the hydrated salt content in the surface ice [10], the largest ejecta fragment, the slope of the cumulative size distribution of the ejected fragments , the slope of the ejecta fragment size-velocity distribution, the strength of Europa's surface material and the maximum ejecta velocity. Variations in each parameter were tested in the dust model and their influence on …