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
History of Mars observation about which the planet moves at a uniform rate of rotation. He proposed that the order of the planets, by increasing distance, was: the Moon, Mercury, Venus, Sun, Mars, Jupiter, Saturn, and the fixed stars. Ptolemy's model and his collective work on astronomy was presented in the multi-volume collection "Almagest", which became the authoritative treatise on Western astronomy for the next fourteen centuries. In the 5th century CE, the Indian astronomical text "Surya Siddhanta" estimated the angular size of Mars as 2 arc-minutes (1/30 of a degree) and its distance to Earth as 10,433,000 km (1,296,600 yojana, where one yojana