Earth's diverse cartographic and geodetic systems are based on reference ellipsoids, all of which are oblate. A science-fiction example of an extremely oblate planet is Mesklin from Hal Clement's novel "Mission of Gravity". The prolate spheroid is the approximate shape of the ball in several sports, such as in rugby football. Several moons of the Solar System approximate prolate spheroids in shape, though they are actually triaxial ellipsoids. Examples are Saturn's satellites Mimas, Enceladus, and Tethys and Uranus' satellite Miranda. In contrast to being distorted into oblate spheroids via rapid rotation, celestial objects distort slightly into prolate spheroids via tidal forces when they orbit a massive body in a close orbit. The most extreme example is Jupiter's moon Io, which becomes slightly more or less prolate in its orbit due to a slight eccentricity, causing intense volcanism. The major axis of the prolate spheroid does not run through the satellite's poles in this case, but through the two points on its equator directly facing toward and away from the primary. The term is also used to describe the shape of some nebulae such as the Crab Nebula. Fresnel zones, used to analyze wave propagation and interference in space, are a series of concentric prolate spheroids with principal axes aligned along the direct line-of-sight between a transmitter and a receiver. The atomic nuclei of the actinide elements are shaped like prolate spheroids. In anatomy, near-spheroid organs such as testis may be measured by their long and short axes. Many submarines have a shape which can be described as prolate spheroid. For a spheroid having uniform density, the moment of inertia is that of an ellipsoid with an additional axis of symmetry. Given a description of a spheroid as having a major axis , and minor axes and , the moments of inertia along these principal axes are , , and . However, in a spheroid the minor axes are symmetrical. Therefore, our inertial terms along the major axes are:  where is the mass of the body defined as