1. Further development of modeling of spatial distribution of energetic electron fluxes near Europa M. V. Podzolko 1, I. V. Getselev 1, Yu. I. Gubar 1, I. S. Veselovsky 1,2 1 Skobeltsyn Institute of Nuclear Physics, Lomonosov Moscow State University, Russia 2 Space Research Institute (IKI), Russian Academy of Sciences, Moscow, Russia – Charged particle flux and radiation dose equatorial profiles at Jupiter – Radiation doses in Europa’s orbit: high hazard – Factors which determine charged particle flux reduction near Europa – Relativistic electron fluxes on Europa’s surface and at 100 km altitude – Radiation doses on Europa’s surface and at 100 km orbit around Europa – Doses during gravity assists using Jupiter’s moons – Conclusions, discussion

2. Equatorial profiles of the integral fluxes of E > 0.5, >2 and >10 MeV electrons and E > 2, >10 and >30 MeV protons at Jupiter. Charged particle flux and radiation dose equatorial profiles at Jupiter Equatorial profiles of radiation doses under 0.27, 1, 2.2 and 5 g/cm 2 shielding, and separately dose under 2.2 g/cm 2 from protons only near Jupiter. GanymedeIoAmaltheaEuropaGanymedeIoAmaltheaEuropa

3. Doses under various shielding in Europa’s (solid line) and Ganymede’s (dash line) orbits. Calculated radiation doses in Europa’s orbit: high hazard g/cm 2 EG 1.02.2·10 6 3.5·10 4 2.28.8·10 5 9.0·10 3 5.02.4·10 5 2.0·10 3 10.04.5·10 4 5.2·10 2 2-month doses in Europa’s and Ganymede’s orbits, rad. Integral fluxes of electrons in Europa’s (solid line) and Ganymede’s (dash line) orbits.

4. Factors which determine charged particle flux reduction near Europa 1.Particle drift speed relative to Europa. 2.Larmor motion of the particles near the surface. 3.Difference of Europa’s orbital plane from Jupiter’s geomagnetic equator plane. 4.Disturbance of Jupiter’s magnetic field in vicinity of Europa. 5.Presence of the electric fields, which can accelerate particles in the magnetosphere. 6.Interaction of particles with Europa’s tenuous atmosphere. 7.Particle diffusion. 8.Thickness and configuration of spacecraft’s shielding.

5. Dependence of electron flux from their drift speed relative to Europa 5 MeV, 0 km >30 MeV<30 MeV Fluxes of Electrons with energies a) 42–65 keV, b) 527– 884 keV from the Galileo EPD data during flyby near Europa. Directions of the longitudinal drift of electrons with energies 30 MeV relative to Europa are shown. Distribution of differential fluxes of 5 MeV electrons on Europa’s surface taking into account only guiding center approximation.

6. Dependence of electron flux from their Larmor motion near the surface 2 3 4 1 Dependency of the allowed range of space angles (upper curve) and flux of electrons of energies 500 keV (middle curve) and 5 MeV (lower curve) from point’s latitude,.taking into account their Larmor motion near the surface.

7. Dependence of electron flux parameters from Europa’s magnetic latitude Europa’s magnetic latitude λ M = 0° L parameter: L = 9.5 R J Magnetic field B/B 0 = 1 Integral flux of >5 MeV electrons F e (>5 MeV) = 8.9·10 6 Integral flux of >10 MeV protons F p (>10 MeV) = 1.4·10 5 Fluxes computed using Divine, Garrett, 1983 model. Europa’s magnetic latitude λ M = 10° L parameter: L = 9.8 R J Magnetic field B/B 0 = 1.26 Integral flux of >5 MeV electrons F e (>5 MeV) = 6.3·10 6 Integral flux of >10 MeV protons F p (>10 MeV) = 8.3·10 4 The period of particle drift speed relative to Europa can be up to 2 times higher.

8. Spatial distribution of relativistic electron fluxes on Europa’s surface Distribution of differential fluxes of electrons with energy 5 MeV on Europa’s surface. J v 5 MeV, 0 km

9. Spatial distribution of relativistic electron fluxes on Europa’s surface Distribution of differential fluxes of electrons with energy 50 MeV on Europa’s surface. Distribution of differential fluxes of electrons with energy 5 MeV on Europa’s surface. J v 5 MeV, 0 km J v 50 MeV, 0 km

10. Spatial distribution of relativistic electron fluxes on Europa’s surface 50 MeV, 0 km 5 MeV, 0 km

11. Electron fluxes on Europa’s surface and at 100 km altitude 50 MeV, 100 km 5 MeV, 100 km5 MeV, 0 km 50 MeV, 0 km

12. Spatial distribution of radiation doses on Europa’s surface 2.2 g/cm 2, 0 km 5 g/cm 2, 0 km

13. Radiation doses on Europa’s surface and at 100 km altitude 5 g/cm 2, 100 km 2.2 g/cm 2, 100 km2.2 g/cm 2, 0 km 5 g/cm 2, 0 km

14. Dependence of dose at 100 km orbit around Europa from its inclination Dependence of the dose under 2.2 (solid line) and 5 g/cm 2 (dash line) at 100 km orbit around Europa. Optimal orbits have inclination >60°.

15. Doses behind 2.2 (upper curves on each plot) and 5 g/cm 2 (lower curves) for one orbital circuit during gravity assists using Europa and Ganimide, depending on the distance of the opposite orbit’s node. Doses during gravity assists using Europa and Ganymede

16. Conclusions, discussion –In Jupiter’s radiation belts and in particular in Europa’s orbit very intensive fluxes of relativistic electrons are present, which will represent the main hazard for spacecraft’s electronic equipment behind the shielding of ≥1 g/cm 2. The radiation hazard in Europa’s orbit is sufficiently higher, than in vicinity of Ganymede. –But near Europa part of the flux is shaded by the moon. This reduction of fluxes is nonuniform and differs for various particle energies and pitch-angles, and for the surface and the low-altitude orbit. Factors, which determine this particle flux reduction have been revealed. They were put in a basis of the model of spatial distribution of energetic particle fluxes near Europa, which is being developed by the authors. –Distribution of relativistic electron fluxes taking into account several of mentioned above factors has been computed. –These computations have shown, that the most intensive fluxes of relativistic electrons of energies <30 MeV precipitate on Europa’s trailing side along its orbital motion. But their fluxes on the surface are several times lower, than at 100 km altitude, and decrease from middle latitudes to equator. – The least hazardous low-altitude orbits around Europa are those with inclination >60°. – Each gravity assist using Europa adds a dose of ≥10 krad behind 2.2 g/cm 2. – Further development of the model is appropriate.