NASA has speculated on the feasibility of mining the atmospheres of the outer planets, particularly for helium-3, an isotope of helium that is rare on Earth and could have a very high value per unit mass as thermonuclear fuel.[1][2] Factories stationed in orbit could mine the gas and deliver it to visiting craft.[3] However, the Jovian system in general poses particular disadvantages for colonization because of the severe radiation conditions prevailing in Jupiter's magnetosphere and the planet's particularly deep gravitational well.
^Robert Zubrin, Entering Space: Creating a Spacefaring Civilization, section: Settling the Outer Solar System: The Sources of Power, pp. 158–160, Tarcher/Putnam, 1999, ISBN1-58542-036-0