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
Extraterrestrial skies (Jupiter, Saturn, Uranus and Neptune) would appear slightly brighter during opposition, but slightly dimmer during conjunction. This effect is most noticeable for Jupiter, and results from Mars' larger orbit compared with that of Earth causing larger variations of interplanetary distance. From Phobos, Mars appears 6,400 times larger and 2,500 times brighter than the full Moon as seen from Earth, and appears as a sphere of angular diameter roughly 42°—taking up a quarter of the width of a celestial hemisphere. From Deimos, Mars appears 1,000 times larger and 400 times brighter than the full Moon as seen from Earth, and appears