Definition of planet Earth's own orbit around the Sun—looking down on the ecliptic, the Moon never actually loops back on itself, and in essence it orbits the Sun in its own right. Also many moons, even those that do not orbit the Sun directly, often exhibit features in common with true planets. There are 19 moons in the Solar System that have achieved hydrostatic equilibrium and would be considered planets if only the physical parameters are considered. Both Jupiter's moon Ganymede and Saturn's moon Titan are larger than Mercury, and Titan even has a substantial atmosphere, thicker than the Earth's. Moons such as
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