Callisto (moon) facilitate remote exploration of Europa, or be an ideal location for a Jovian system waystation servicing spacecraft heading farther into the outer Solar System, using a gravity assist from a close flyby of Jupiter after departing Callisto. In December 2003, NASA reported that a manned mission to Callisto might be possible in the 2040s. Callisto (moon) </math>.</ref> Callisto (Jupiter IV) is the second-largest moon of Jupiter, after Ganymede. It is the third-largest moon in the Solar System after Ganymede and Saturn's largest moon Titan, and the largest object in the Solar System not to be properly differentiated. Callisto was discovered
Ring Around the Moon (Space: 1999) from the sphere and enveloped the Moon. Tracking sensors reveal the sphere to be stationary but, from their perspective, it is still getting closer to the Moon's surface; John Koenig realises that the Moon has been trapped in an orbit around the sphere. An audio signal is received and a sibilant voice announces that they are prisoners of the planet Triton. The staff reviews the damage caused by the Moon's sudden deceleration. The fact that all but four are non-operational and the main generators show no sign of damage but are only putting out minimum power indicates that the sphere's