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
Terraforming of Mars in atmospheric water vapor, but Mars does not retain enough carbon dioxide that could practically be put back into the atmosphere to warm it. Importing greenhouse gases, although impractical, is a concept to be studied, but similarly suffers from the problem that Mars is unable to hold onto very much atmosphere. Future population growth, demand for resources, and an alternate solution to the Doomsday argument may require human colonization of bodies other than Earth, such as Mars, the Moon, and other objects. Space colonization will facilitate harvesting the Solar System's energy and material resources. In many respects, Mars is the