High energy radiation environments of the Jupiter and Saturn systems - impacts and mitigation

Details High energy radiation environments of the Jupiter and Saturn systems - impacts and mitigation High energy radiation environments of the Jupiter and Saturn systems - impacts and mitigation

Sep 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008epsc.conf..118c&link_type=abstract

European Planetary Science Congress 2008, Proceedings of the conference held 21-25 September, 2008 in Münster, Germany. Online a

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Future spacecraft missions to the Jupiter and Saturn systems, and the continuing Cassini orbital tour at Saturn, face many challenges of survival and useful scientific operations in the magnetospheric radiation environments of these systems. The most extreme energetic particle radiation fluxes are found in the orbital regions of Io to Europa at Jupiter and at lesser intensity within the orbit of Enceladus at Saturn. Energetic keV to MeV "killer" electrons and protons are the primary penetrating radiation components in both environments. The higher maximum GeV energies of the Saturn protons from cosmic ray albedo neutron decay (CRAND), and secondary gamma rays and neutrons from high energy particle interactions with spacecraft shielding, moon surfaces, and planetary rings, gives these penetrating radiation components deep impact. Proximity to the strong planetary magnetic field of Jupiter, and to the main ring source of CRAND neutrons at Saturn, make the innermost radiation environments of special concern for highly penetrating and potentially high flux particle irradiation in lesserknown regions inwards of the planetary rings. The low-intensity galactic cosmic ray ions penetrating easily into the outer reaches of the giant planet radiation belts, e.g. at the orbits of Ganymede and Titan, cannot however be ignored, since single event upsets from individual heavily-ionizing heavy ions can have disruptive effects on spacecraft electronics. Impact of magnetospheric irradiation can have measurable effects on moon surfaces, particularly at higher flux levels in the Jupiter system where the icy Galilean moon surfaces are chemically affected and secondary x-ray emission is detected from Europa. Since energetic heavy ion irradiation ejects surface ions and neutral molecules into the local space environment, this irradiation can enable remote ionneutral particle measurements of surface composition from moon orbit at far higher elemental and even isotopic mass resolution than available from remote optical spectroscopy. Any local surface hotspots of fresh emergence for oceanic chemicals and astrobiological materials (biominerals and organics) could potentially be identified from global orbital surveys. Ongoing surface activity is easily apparent at Enceladus but not so at Europa, and we continue to consider whether exogenic energy flux and resultant radiolytic chemistry may impact interior dynamics of these two moons and other bodies in these systems. It is already evident that cumulative Enceladus outgassing has major impact on energetic ion intensities in the inner magnetosphere of Saturn. Careful consideration of moderating influences on charged particle irradiation can provide effective mitigation strategies to cope with extreme radiation in selected environments. Distance from the central planet into weaker magnetic field substantially increases potential lifetimes of spacecraft with limited tolerance for irradiation but advanced capabilities for remote observations of the planetary system. Flybys or orbital operations at Io and Europa are of great science interest but impose expensive mass requirements for radiation shielding, and orbital operations at Ganymede and Titan are far less demanding of such resources. Natural Ganymede magnetic, Europa hemispheric, and local surface topographic shielding can be utilized to extend mission lifetimes and assure more successful science observations.

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