Colonization of the outer Solar System of the four Galilean moons. Despite this, its volcanoes could be energy resources for the other moons, better to colonize. The Artemis Project proposed a plan to colonize Europa. Scientists would inhabit igloos and drill down into the Europan ice crust, exploring any subsurface ocean. The report also discusses use of air pockets for human habitation. Ganymede is the largest moon in the Solar System. Ganymede is the only moon with a magnetosphere, but it is overshadowed by Jupiter's magnetic field. Ganymede receives about 8 rem of radiation per day. Due to its distance from Jupiter's powerful radiation belt, Callisto
Planet Nine and proposed a possible orbit for the planet. This hypothesis could also explain TNOs with orbits perpendicular to the inner planets and others with extreme inclinations, as well as the tilt of the Sun's axis. Planet Nine is hypothesized to follow a highly elliptical orbit around the Sun with a period lasting 10,000–20,000 years. The planet's semi-major axis is estimated to be , roughly 20 times the distance from Neptune to the Sun, and its inclination to the ecliptic, the plane of the Solar System, to be about . The high eccentricity of Planet Nine's orbit could bring it as