Colonization of the outer Solar System the Solar System's gas giant planets for exploration and possibly mining of helium-3, which could have a very high value per unit mass as a thermonuclear fuel. The Jovian system in general has particular disadvantages for colonization, including its severe radiation environment and its particularly deep gravity well. Its radiation would deliver about 3,600 rems per day to unshielded colonists on Io and about 540 rems per day to unshielded colonists on Europa. Exposure to about 75 rems over a few days is enough to cause radiation poisoning, and about 500 rems over a few days is fatal. Jupiter itself,
Sagan Planet Walk Sagan, Bill Nye, narrated a podcast tour of the Planet Walk in 2006 which can be accessed free by calling 703.637.6237 as you walk through the scale-model representation of the Solar System. The models of the Solar System, in order: The Sagan Planet Walk has inspired the creation of other scale-model Solar Systems in the United States. Sagan Planet Walk The Sciencenter's Sagan Planet Walk is a walkable scale model of the Solar System, located in Ithaca, New York. The model scales the entire Solar System—both planet size and distances between them—down to one five billionth of its actual size.