Depth Dose Exposures in the Magnetosphere of Jupiter at the Icy Moons: Callisto, Ganymede, and Europa

摘要

The highly successful Galileo mission made a number of startling and remarkable discoveries during its eight-year tour in the harsh Jupiter radiation environment. Two of these revelations were: 1) salty oceans lying under an icy crust of the Galilean moons: Europa, Ganymede and Callisto, and 2) the possible existence or remnants of life, especially on Europa, which has a very tenuous atmosphere of oxygen. Galileo radiation measurement data from the Energetic Particle Detector (EPD) have been used (Garrett et al., 2003) to update the trapped electron environment model, GIRE: Galileo Interim Radiation Environment, in the range of L (L: McIlwain parameter) 8-16 Rj (Rj: radius of Jupiter is equivalent to 71,400 km) with plans to extend the model for both electrons and protons as more data are reduced and analyzed. In this paper the current GIRE model and high-energy transport codes have been used to compute depth dose exposures as a function of spacecraft shielding thickness for specified times in orbit at Callisto (Rj is equivalent to 26.6), Ganymede (Rj is equivalent to 15), and Europa (Rj is equivalent to 9.47). During its mission, Galileo encountered a number of radiation-induced anomalies; in fact, few Galileo spacecraft systems were unaffected by the radiation environment. The results presented in this paper can be applied to utilize shielding effectively and possibly minimize potential radiation-induced anomalies on future Jupiter spacecraft.