Exploration of Jupiter disadvantages for colonization because of the severe radiation conditions prevailing in Jupiter's magnetosphere and the planet's particularly deep gravitational well. Jupiter would deliver about 36 Sv (3600 rem) per day to unshielded colonists at Io and about 5.4 Sv (540 rems) per day to unshielded colonists at Europa, which is a decisive aspect due to the fact that already an exposure to about 0.75 Sv over a period of a few days is enough to cause radiation poisoning, and about 5 Sv over a few days is fatal. Ganymede is the Solar System's largest moon and the Solar System's only
Names of the days of the week nundinal cycle with the seven-day week. Our earliest evidence for this new system is a Pompeiian graffito referring to the 6th February ("viii idus Februarius") of the year AD 60 as "dies solis" ("Sunday"). Another early witness is a reference to a lost treatise by Plutarch, written in about AD 100, which addressed the question of "Why are the days named after the planets reckoned in a different order from the actual order?". The days were named after the planets of Hellenistic astrology, in the order Sun, Moon, Mars ("Ares"), Mercury ("Hermes"), Jupiter ("Zeus"), Venus ("Aphrodite") and Saturn ("Cronos"). The