Ganymede’s and Europa’s Neutral Imaging Experiment (GENIE) at the Jupiter’s icy moons

1. Ganymede’s and Europa’sNeutral Imaging Experiment (GENIE) at the Jupiter’s icy moons A. Milillo, and the GENIE Team

2. Ganymede’sand Europa’sNeutral Imaging Experiment (GENIE) GENIE is a high-angular-resolution detector of EnergeticNeutralParticles(energy range 10s eV – few keV) (ENP) based on the ToF technique, optimizedtoflown in the Jupiter’s environment. Its objective is to map the origin sites of the ENP of the icy moons’ exospheres, in order to investigate the interaction between the surface and the environment. Golden Age of of Solar System Exploration

3. Ion impact ontoan icysurface Intense ion fluxes impacting onto the icy moons’ surfaces produce neutral particle release that originates the exospheres. The observations at proper angular resolution of the higher-energy neutrals produced by the plasma-surface interaction will provide an instantaneous2D imaging. Golden Age of of Solar System Exploration

4. Comparative observations Similarenergeticionfluxesare expectedatEuropa and Ganymede, composed by a similaricedsurfacebut with the difference of an internalmagneticfieldthatcouldshield the plasma or definepreferential entries and plasma precipitationregions On the contrary, the ionfluxesatCallisto are considerablylower. Similarobservations in differentenvironmentlike the threemoonswouldoffer the chance to investigate the satellitesevolution in the Jupitersystem. Golden Age of of Solar System Exploration

5. Europa vs Ganymede Europa is the simplest case since it has not an internal magnetic field. The plasma precipitation is just due to the interaction with the obstacle. The release variations at low spatial scale are mainly driven by different surface properties. Ganymede with its internal magnetic field has a complex interaction with the Jupiter’s magnetospheric plasma. Golden Age of of Solar System Exploration

6. Surface releasedvelocityspectra@ Europa Major components of released particles are H2O (produced by direct ion sputtering), O2and H2(produced by radiolysis and sputtering). H (via ion back scattering) could be relevant at velocities above 100 km/s. (Plainaki et al., 2011, Icarus). Escape velocity: 2 km/s Golden Age of of Solar System Exploration

7. Neutralparticlesrelease @ Europa Leading Leading Detection of ENP at high spatial resolution from the surface will permit to investigate the global asymmetries and to relate the local surface release efficiency to surface features and purity of ice. This will be an important piece of the evolution puzzle. Trailing Trailing H2O released by H+, O+ andS+sputtering. Note that IS is a stochiometric process, so it releases all the species trapped into the surface. O2releasedby H+, O+ andS+ impact and radiolysis The ENP differential flux above 10 eVfrom the surface can be estimated about 5·108p.cle/(cm2 s sreV) at Europa (Plainaki et al., Icarus, 2012). Golden Age of of Solar System Exploration

8. Ganymede’ssurface Ganymede is the unique discovered moon in the Solar system with a dipolar magnetic field. Very close correspondence has been demonstrated between the observed higher-albedo polar cap boundary and open/closed field lines boundary (Khurana et al., 2007). Golden Age of of Solar System Exploration

9. Ganymede’smagnetosphere 100 keV 10 keV 1 keV (Jia et al. 2008) (Massetti courtesy, 2011) The Jupiter’s plasma overcomes the moon from the trailing side. At Ganymede, as in the Mercury’s case, the fluxes precipitate in the open-field lines areas. Golden Age of of Solar System Exploration

10. ENP release @ Ganymede The magnetic field permits the exosphere generation only in specific regions. Detection of ENP at high spatial resolution from the surface will permit to dynamically map the precipitating regions (auroral mapping) and to relate them to surface features (like different albedo). This is a kind of second vantage point observation for precipitating plasma. This will be an outstanding new way to investigate the coupling between the Jupiter’s plasma and the Ganymede’s magnetic field. Jupiter Trailing Leading Leading O+ FLUX (cm-2 s-1 keV-1) 1-keV O+ simulations by Massetti in the MHD magnetic field model by Jia et al., 2008 H2O released by O+ sputteringsimulation by Mura Golden Age of of Solar System Exploration

11. Primary and synergic GENIE science goals • For each Galiean moon: Ganymede, Europa and Callisto, GENIE is aimed: • To characterize in space and in energy the radiating component of the exospheres; • To study the interactions of the moons with the Jovian magnetosphere; • To discriminate and depict the exospheresgeneration mechanisms. • Moreover, the possibility to operate GENIE at the three moons permits • To compare the different environments. • Synergic science goals with other JUICE payload experiments are: • To characterize the complete exospheric energy distribution • with INMS and UV spectrometer; • To characterize the surface release process • with Particle Package and magnetometer; • To investigate weathering and erosion of surface features; • with Surface multi-wavelength spectroscopy; • To determine how much the Ganymede escape influence the Jupiter’s aurorae • with Particle Package, magnetometer and UV imaging. Golden Age of of Solar System Exploration

12. GENIE pointing To see the surface emission, the sensor must point toward the moon surface (nadir). For instance, in order to resolve surface features of the order of 30 km, an angular resolution of about 5 degrees is required from an altitude of 350 km above the moon surface. Golden Age of of Solar System Exploration

13. GENIE basic concept • Entrance 5°x60° with ion deflector. • START section: Shutter System (BC/SERENA-ELENA heritage) • ToF chamber • STOP section: signal detection system • Anticoincidence section: background detection system. Golden Age of of Solar System Exploration

14. Heritage at IAPS SERENA/ELENA will be delivered to ESA in mid 2013 High-angular resolution low-energy neutral atom detectionby means of micro-shuttering techniques Golden Age of of Solar System Exploration

15. BepiColombo-MPO/SERENA-ELENA • The basic sections of ELENA sensor are: • a charge particle deflector for ions suppression; • an entrance with a grating system which may work as: • a shuttering system, based of coupled moving slits of nanometric dimension, which permits the neutrals to enter in the sensor only when the slits are aligned, defining the detection START time. • UV suppressor; • a ToF chamber; • a STOP system based on the technique of MCP technologies. Golden Age of of Solar System Exploration

16. Example: ELENA shutter at 10 kHz At MEFISTO facility in Bern University, the functionality of the ELENA shutter has been tested to verify the open/closed timing. 1-keV-H beam through the shuttering system detected by the MCP. Golden Age of of Solar System Exploration

17. Conclusions • Without ENP observations there is no way to univocally relate the exosphere to surface features and to monitor instantaneously the effect of plasma precipitation onto the surface. • ENP investigation is the link between magnetospheric science and surface science. • ENP detection could be a support for interpreting other instrument observations. • This kind of measurement is new, especially for icy surfaces where sputtering is the dominant process; hence, any observation will produce a big science return. • ENP observations are feasible, even if the noise issue must be carefully addressed, especially during the Europa flybys. • GENIE has no strong constraints (distances or pointing requirements) for the spacecraft. • The required GENIE resources are not demandingfor the spacecraft. Golden Age of of Solar System Exploration