 Ganymede is the Solar System 's largest moon and the Solar System 's only known moon with a magnetosphere , but this does not shield it from cosmic radiation to a noteworthy degree , because it is overshadowed by Jupiter 's magnetic field . Ganymede receives about 0 @.@ 08 Sv ( 8 rem ) of radiation per day . Callisto is farther from Jupiter 's strong radiation belt and subject to only 0 @.@ <unk> Sv ( 0 @.@ 01 rem ) a day . For comparison , the average amount of radiation taken on Earth by a living organism is about 0 @.@ <unk> Sv per year ; the highest natural radiation levels on Earth are recorded around <unk> hot springs at about 0 @.@ 26 Sv per year . 
