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
Origin of the Moon that two bodies—each five times the size of Mars—collided, then re-collided, forming a large disc of debris that eventually formed Earth and the Moon. The paper was called “Forming a Moon with an Earth-like composition via a Giant Impact,” by R.M Canup. A 2012 study on the depletion of zinc isotopes on the Moon supported the giant-impact origin for Earth and the Moon. In 2013, a study was released that indicated that water in lunar magma is indistinguishable from carbonaceous chondrites and nearly the same as that of Earth in isotopic composition. The giant-impact hypothesis was again challenged in September