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
Colonization of Mars missions, as the "Apollo" missions to the Moon were not planned to be sites of a permanent base. Colonization requires the establishment of permanent habitats that have potential for self-expansion and self-sustenance. Two early proposals for building habitats on Mars are the Mars Direct and the Semi-Direct concepts, advocated by Robert Zubrin. As of 2019, SpaceX owner Elon Musk is funding and developing a series of Mars-bound cargo flights with the BFR rocket and spaceship system as early as 2022, followed by the first crewed flight to Mars on the next launch window in 2024. During the first phase, the